PDA

View Full Version : If time travel to the past is possible..........

levi
2nd January 2012, 09:00 PM
would the saying you only have certain amount time alive be true?

Complexity
2nd January 2012, 09:30 PM
Yes and no.

JJM 777
2nd January 2012, 10:01 PM
you only have certain amount time alive
True:

If (and when) time travel into your own personal past is impossible, and your body is constantly ageing, and there are limits to how much ageing your body can endure (with current medical knowledge the maximum is around 120 years), and the medical science will not invent a way to rejuvenate our bodies to the extent of effective immortality:

You only have a limited amount of time alive.

Molinaro
2nd January 2012, 11:43 PM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?

Pulvinar
2nd January 2012, 11:53 PM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past?

Not to say it's possible, but see the movie Primer-- they solved that one. I won't spoil it.

Molinaro
2nd January 2012, 11:57 PM
I've seen the movie.

Halfcentaur
3rd January 2012, 02:31 AM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?

This is why you can never ever go back to the same place something happened, which lots of people don't seem to realize at first glance.

People like to think they are standing in the place something historic happened when visiting memorials and what not, but it's more like the earth is a car perpetually driving through new terrain, and we can only visit the place in the car where something happened, but not where the car actually was when it happened.

This used to freak me out as a kid. And it's something time travel plots never seem to factor in.

Halfcentaur
3rd January 2012, 02:32 AM
Not to say it's possible, but see the movie Primer-- they solved that one. I won't spoil it.

Primer is my favorite time travel story, but I haven't watched it in about 7 years or so. I didn't recall this being touched on, I need to endure the movie again.

dlorde
3rd January 2012, 03:29 AM
In the traditional Time Machine of fiction, even assuming you could allow for the spatial displacement, if the temporal translation was effectively instantaneous (direct from present to designated past time), then unless you wore a spacesuit and translated into hard vacuum, you'd suddenly occupy the same space as something else (air?), which would not be pleasant. But would time travel take time - would you age as you traveled? is there a cosmic speed limit like c?

If the temporal translation was progressive (moving back through time moment by moment), I don't see how you could make significant allowance for spatial displacement, and in the first yoctosecond you'd occupy roughly the same space as you'd just been in before activating the machine - two of you occupying one volume. Probably not nice, and it would surely gum up the works (of both the machine and you).

In more realistic physics, a spacetime wormhole seems more plausible (but probably not The Time Tunnel (http://en.wikipedia.org/wiki/The_Time_Tunnel)!), but Hawking says that you'd need negative energy to produce one, it would be very small, and it would collapse if anything tried to go through. Apart from that, I've always wondered whether, if you made a big one, stuff could move either way through it - matter drifting into the distant future passing matter drifting into the distant past, and whether both ends would have to be in hard vacuum, e.g. could one end open in a star and cause high pressure stellar plasma to burst through into the future (or past). Not good if the other end is in your lab... ;) Plus, what would happen if you opened a wormhole as far back as the pre-inflation big bang? would the universe turn inside out?

You can apparently get sufficient distortions of spacetime inside the event horizon of large rotating black holes to create closed timelike curves, allowing travel into the past. But the obvious problem is how to get out again...

Here's an interesting QM discussion (http://arxiv.org/abs/1007.2615) on resolving the time travel problem.

Roger Ramjets
3rd January 2012, 03:45 AM
Time travel into the past is definitely possible.

Only problem is that you age backwards (along with the rest of the Universe) and when you come back to the present nothing has changed, so you don't remember doing it.

psionl0
3rd January 2012, 03:49 AM
If one could travel back along his own timeline then he would create more contradictions than just the question of dying (I think these paradoxes have been dealt with many times on this forum).

OTOH if time travel means going to parallel universes then time travel would have no direct effect on how many years pass on your personal calendar before you die.

Dancing David
3rd January 2012, 05:22 AM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?
You need a space ship as well, the earth goes around the sun, the sun moves around the galaxy, the galaxy moves around our cluster....

:)

Roboramma
3rd January 2012, 07:40 AM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?

There is no absolute reference frame.

Imagine you did have a time machine that can go back in time. You don't bother specifying the coordinates in space that you want it to send you, you just decide to go back in time one day. Where do you end up? Where the earth was yesterday? Where it is today? Where you would have been if you'd been following a straight line trajectory for one day?

Physics doesn't have an answer. But that's not a problem with time travel, it's a problem with teleportation. You can't say here this many days ago, without specifying a reference frame. Nor can you say there at this time, without specifying a reference frame.

If a time machine worked the way you seem to be suggesting, it would falsify relativity.

Farsight
3rd January 2012, 10:11 AM
Sorry to spoil anybody's fun here, but backward time travel is impossible because we don't even travel forward in time. It's just a figure of speech. Things move through space. Clocks "clock up" things that move through space, usually in some cyclic fashion, and show a cumulative total of that motion as "the time". And there's no such thing as negative motion. If something has moved and you move it back, that's more motion, not negative motion. Think it through and you'll see the sense of it. And check out A World Without Time: The Forgotten Legacy of Godel and Einstein (http://www.amazon.co.uk/World-Without-Time-Forgotten-Einstein/dp/0713993871/ref=sr_1_1?s=books&ie=UTF8&qid=1325613535&sr=1-1). Time exists like heat exists, but it isn't something that flows or through which we move. And that means time travel is science fiction.

You can maybe get a better handle on it via the stasis box (http://en.wikipedia.org/wiki/Stasis_(fiction)). That’s science fiction too. It’s like the ultimate refrigerator. No motion occurs inside the box, so when I put you inside it, nerve impulses and electromagnetic phenomena don’t propagate. So you can’t see, you can’t hear, and you can’t even think. Hence when I open the door 5 years later, to you it’s like I opened the door just as soon as I closed it. You “travelled” to the future by not moving at all. Instead everything else did.

AvalonXQ
3rd January 2012, 10:20 AM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?

Why do you assume that an object flung backward in time suddenly breaks loose from its surroundings?

Consider H.G. Wells (you're still on Earth and subject to gravity, etc, while your vehicle "moves" forward or backward) or the show Seven Days (you're in orbit around the Earth while you move backward).
Here on Earth, Earth's gravity dominates our navigation; I don't need to take into account anything outside of the planet when I aim my trebuchet, for instance. No reason to think this changes for time travel.

JJM 777
3rd January 2012, 10:41 AM
we don't even travel forward in time.
(...)
Things move through space. Clocks "clock up" things that move through space, usually in some cyclic fashion, and show a cumulative total of that motion as "the time".
Hmmm.

Let me serve a ball to you -- Roboramma will hit back at whatever you reply to this, but hopefully not before you swallow the bait:

If we donīt travel in time at all (if this was your intention), we only travel in space, do you mean that only one moment of "time" exists, all existence of matter in the universe is simultaneous, and the only thing what moves are the simultaneously existing matter in relation to each other? No past exists, no future exists, only the present moment exists.

kbm99
3rd January 2012, 11:03 AM
This is why you can never ever go back to the same place something happened, which lots of people don't seem to realize at first glance.

People like to think they are standing in the place something historic happened when visiting memorials and what not, but it's more like the earth is a car perpetually driving through new terrain, and we can only visit the place in the car where something happened, but not where the car actually was when it happened.

This used to freak me out as a kid. And it's something time travel plots never seem to factor in.

Greg Benford's 1981 novel "Timescape" covers that point very well, actually. Tachyon-using physicists attempting to send a message back in time by 30 or so years must very carefully aim the tachyon beam so as to intersect the earth's previous location. He was the first person I read to address that particular point and I thought it rather interesting.

Soapy Sam
3rd January 2012, 11:36 AM
I don't see why I'd fly off into space if I travelled back in time.
I don't fly off into space when I travel forward in time.

The point about SF "Time Travel" is that the traveller moves independently of everyone else's experience of time, which is wherein the interest of the story lies.

If we postulate that reversing time reverses it universally, the traveller would simply find himself back where he was at the time he selected as target. If he selected a point before his own birth, he would find himself as a foetus inside his mama.
Any time machine would revert to it's constituent minerals, spread around the world.
In short the whole thing would never have happened.
Which would make for a dull story. But may explain the dearth of travellers from the future.

Molinaro
3rd January 2012, 11:37 AM
Why do you assume that an object flung backward in time suddenly breaks loose from its surroundings?

Consider H.G. Wells (you're still on Earth and subject to gravity, etc, while your vehicle "moves" forward or backward) or the show Seven Days (you're in orbit around the Earth while you move backward).
Here on Earth, Earth's gravity dominates our navigation; I don't need to take into account anything outside of the planet when I aim my trebuchet, for instance. No reason to think this changes for time travel.

It depends entirely on the proposed mechanism for the time travel. It's not uncommon for time travel to be depicted as disappearing at one time/place and reappearing at another time/place. Other times it's depicted as a journey in a vehicle. Other times it's depicted as passing through some other dimension or sub-space. Other times it's depicted as being limited to a time span during which the time machine itself has existed, so that you can step into it and then out of it at any time since the machine was 1st built.

Remaining gravity bound to the earth or not during your time travel would depend on which fictitious means of time travel is being considered.

AvalonXQ
3rd January 2012, 12:07 PM
It depends entirely on the proposed mechanism for the time travel.

Absolutely it does, which is why the arguments put forward as to why time travel is impossible are almost universally nonsense.

It's perfectly reasonable to explain why a carefully-specified mechanism for time travel may be impossible, but it is rather ridiculous to address the notion of time travel by some unknown mechanism as though we understand all possible mechanisms well enough to give an educated opinion.

Soapy Sam
3rd January 2012, 12:38 PM
Nonsense.
Anyone who has read Finkelstein's "All possible methods of fictional time travel", (Oxford University Press 2034) is quite familiar with all the possible mechanisms.

catsmate1
3rd January 2012, 04:29 PM
Nonsense.
Anyone who has read Finkelstein's "All possible methods of fictional time travel", (Oxford University Press 2034) is quite familiar with all the possible mechanisms.
Meh, I refer you to Noon's 'Introduction to Polytonic Etiology' [Phaxet Publishing, Tychograd, 2534CE]. It's particularly good on the 'Holmes field' and the interactions between its exotic pseudo-gravitic hytertime field and conventional gravity.

dlorde
3rd January 2012, 04:45 PM
Anyone who has read Finkelstein's "All possible methods of fictional time travel", (Oxford University Press 2034) is quite familiar with all the possible mechanisms.
Ah yes. I think it's coming back to me - I'll remember it in due course...

levi
3rd January 2012, 05:15 PM
Yes and no.

what do you mean yes and no?

Don At Work
3rd January 2012, 05:17 PM
"Time is an illusion. Lunchtime doubly so."

Yeggster
3rd January 2012, 05:20 PM
I thnk we can look to science fiction for some answers ... time travle is basicly fiction anyway.

There is a theory. There could be some logic to the belief that time is fluid, like a river-- with currents, eddies, backwash. And the same currents that swept McCoy to a certain time and place might sweep us there, too. Unless that is true, Captain, we have no hope.

Don At Work
3rd January 2012, 05:22 PM
Another reference book:
Most readers [of Dr. Dan Streetmentioner's Time Traveler's Handbook of 1001 Tense Transformations] get as far as the Future Semiconditionally Modified Subinverted Plagal Past Subjunctive Intentional before giving up; and in fact in later editions of the book all pages beyond this point have been left blank to save on printing costs.

Dancing David
3rd January 2012, 05:23 PM
Why do you assume that an object flung backward in time suddenly breaks loose from its surroundings?

Consider H.G. Wells (you're still on Earth and subject to gravity, etc, while your vehicle "moves" forward or backward) or the show Seven Days (you're in orbit around the Earth while you move backward).
Here on Earth, Earth's gravity dominates our navigation; I don't need to take into account anything outside of the planet when I aim my trebuchet, for instance. No reason to think this changes for time travel.

That is like saying i can board a train at 2:30 when it doesn't arrive until 5:30 because there is a track.

Dancing David
3rd January 2012, 05:24 PM
I don't see why I'd fly off into space if I travelled back in time.
I don't fly off into space when I travel forward in time.

Really, so where was the earth three months ago?

Roboramma
3rd January 2012, 05:27 PM
Really, so where was the earth three months ago?

In which reference frame?

AvalonXQ
3rd January 2012, 05:30 PM
That is like saying i can board a train at 2:30 when it doesn't arrive until 5:30 because there is a track.

Once I'm on the train, I can leave the dining car at noon and return to the dining car at 6 pm, even though the dining car moved from New York City to Rochester.

Why do you assume that I leave, or can ignore, Earth's gravity when I travel through time?

gnome
4th January 2012, 06:55 AM
Here's an interesting one--what if you could travel back in time... but only with a rewind button--you just roll back everything that happened and get to continue again from a designated point.

Life could be pretty sweet if I had a tool that allowed RL save-scumming :)

Soapy Sam
4th January 2012, 07:20 AM
Really, so where was the earth three months ago?

Same place it is now, relative to my house. (Which is where I park the time piano).

Do bear in mind we're talking fiction here.

Time travel seems to suppose we can move "through" say 100 years at a rate far greater than 1 year / year.
But presumably even the "fastest" time machine(whatever the hell that means) , must start at 0 years / year (gauge) and "accelerate". So after you go back zero point five seconds, you already know whether the "left behind effect " is real. (ie you sink into the ground, or fall into the sky. )

This would , if properly used, permit the existence of "time cranes" (or skyhooks) which could not only lift infinite loads to orbit at zero cost, but could do so yesterday.

Now this might lead to an entirely new departure in time travel fiction.
Yesterday.

Pulvinar
4th January 2012, 07:21 AM
Here's an interesting one--what if you could travel back in time... but only with a rewind button--you just roll back everything that happened and get to continue again from a designated point.

Life could be pretty sweet if I had a tool that allowed RL save-scumming :)

everything?

That's quite possible if you truly include everything. Simply consider now as being the future, rolled back. Of course the replay is exactly the same, including the creation of your memories.

Farsight
4th January 2012, 08:15 AM
Hmmm. Let me serve a ball to you -- Roboramma will hit back at whatever you reply to this, but hopefully not before you swallow the bait:No probs. I'm not kidding about all this. Godel and Einstein worked it out in 1942, but few people have heard about it. It's a bit like presentism, and relativity is typically considered to employ eternalism. But it isn't really presentism, it's just a change in emphasis from you need time to have motion to you need motion to have time.

If we donīt travel in time at all (if this was your intention), we only travel in space, do you mean that only one moment of "time" existsNo. The revised concept gives precedence to motion. So only one moment of time exists translates into only one infinitesimal segment of motion exists. And that's like saying things don't move at all. That isn't how the world is. Things move. If they didn't, you couldn't see, think, etc etc. In fact, you wouldn't have even developed. Nor would anything else.

All existence of matter in the universe is simultaneous, and the only thing what moves are the simultaneously existing matter in relation to each other?You can't quite say that either, because "simultaneous" is a reference to time, and time is a measure of how much motion has happened. That measure is altered when you move fast or if you move to a region of low gravitational potential. What you can say is Light and matter and particles and fields exist, these things move in relation to each other, and the thing we call "now" is our measure of how much moving has occurred.

No past exists, no future exists, only the present moment exists.No. It's light and matter and particles and fields that exist, and their motion. Not the past, and not the future. You can't even say that "now" exists because it's infinitesimal. If you only exist for an infinitesimal "length of time" you don't exist at all.

Dancing David
4th January 2012, 08:54 AM
Once I'm on the train, I can leave the dining car at noon and return to the dining car at 6 pm, even though the dining car moved from New York City to Rochester.

Why do you assume that I leave, or can ignore, Earth's gravity when I travel through time?

If you are on the car and then move to where the car was three hours ago, well then the train is a dragon pulling a chariot.

:D

My main point is that you have to translocate through space to travel in time to where the earth was three months ago. If you just shift through the time 'dimension' from x,y,z,t to x,y,z,(t=3months ago), you will most likely be in space , then you also have to make the translation to all four variables to where the art was at T=three months ago.

Vorpal
4th January 2012, 09:16 AM
My main point is that you have to translocate through space to travel in time to where the earth was three months ago. If you just shift through the time 'dimension' from x,y,z,t to x,y,z,(t=3months ago), you will most likely be in space , then you also have to make the translation to all four variables to where the art was at T=three months ago.
Why do you assume Earth wasn't right here three months ago?

In which reference frame?
^Very relevant.

gnome
4th January 2012, 09:18 AM
Exactly... whence the assumption that space is an absolute?

Halfcentaur
4th January 2012, 09:34 AM
Why do you assume that an object flung backward in time suddenly breaks loose from its surroundings?

Consider H.G. Wells (you're still on Earth and subject to gravity, etc, while your vehicle "moves" forward or backward) or the show Seven Days (you're in orbit around the Earth while you move backward).
Here on Earth, Earth's gravity dominates our navigation; I don't need to take into account anything outside of the planet when I aim my trebuchet, for instance. No reason to think this changes for time travel.

I guess this is only applicable to the time travel stories that explicitly require a person to be in the same place something happened to go back in time to the same point.

I guess if you look at it like a VCR tape that is on rewind, then the entire universe goes into reverse to the point you're wanting to pinpoint.

AvalonXQ
4th January 2012, 10:47 AM
My point is very simple -- in all known forms of travel, including land, sea, air, and even space travel -- the Earth drags us with it. We don't have to take into account the sun traveling around the center of the Galaxy, because we're traveling with the Earth.

There is no reason to believe that the same won't happen with time travel.

sphenisc
4th January 2012, 11:06 AM
If time travel to the past is possible..........we could rerun this thread without everyone fighting the hypo.

Dancing David
4th January 2012, 04:32 PM
Why do you assume Earth wasn't right here three months ago?

^Very relevant.

I don't know, some conventional notion that it goes around the sun, as seen from another position. So it would be closer to the line of the fall equinox.

I guess I am being dense.

alexi_drago
4th January 2012, 05:26 PM
It's all explained here:

http://johntitor.strategicbrains.com/TimeMachine.cfm

Skeptic believer
5th January 2012, 11:16 AM
Before anyone talks about time travel to the past, I want you to explain to me how you are going to land at a safe spot on the earth when you get to your desired point in the past? Does your time machine also move you through space, because I can assure you that 3 days ago the earth was not in the same place.

And how accurately could anyone fix a location on earth at any significant point in the past? Could you specify the coordinates of your living room 1 month ago accurately enough so that you don't land in a wall, or the floor, or 30m up above your house? Wouldn't you need to factor in that the earth revolves on it's axis, orbits the sun, co-orbits the center of mass of the earth-moon system, orbits the milky way with the sun, and the milky way's motion in our local cluster?

Fine, you go 6 months into the past, but where will you be? How are you going to aim at a proper location for your arrival?

Funnily enough, I see that as the least of the problems.
If we assume that we emerge in a place which could be described as 'Extrapolated Relative motion', then this gives us a specific point of emergence.
The main problem after that is to make absolutely sure that you've calculated it correctly!!
I think that with the aid of computers, this would be very simple.

I hope you dont mind me going off on a tangent just for a second - but I see a great similarity with this sort of calculation, and the 'exact' calculation of the distance in the latest 'Neutrino' experiment -
They also had to take into account all sorts of rotational motions - and apparently they have been able to do it accurately to know the exact distance the neutrino travels.
If they can do that, then it would be easy to do what boils down to a very similar sort of calculation for the time machine trajectory through space

alexi_drago
5th January 2012, 01:05 PM
How do you seperate from yourself? I mean you can travel through time at different rates due to velocity and gravity but there's only ever one of you and your atoms but when you start traveling backwards, at any time that the time traveling crosses there are two of you and all your atoms.

AvalonXQ
5th January 2012, 01:25 PM
How do you seperate from yourself? I mean you can travel through time at different rates due to velocity and gravity but there's only ever one of you and your atoms but when you start traveling backwards, at any time that the time traveling crosses there are two of you and all your atoms.

In relativity, the concept of "at any time" is somewhat illusory. What is simultaneous in one reference frame is not simultaneous in another.

The fact that you happen to be in two different places "at once" doesn't break any important principles; in fact there's no reason to believe that there's any unusual connection between the two sets of particles other than sharing a worldline.

alexi_drago
5th January 2012, 01:37 PM
In relativity, the concept of "at any time" is somewhat illusory. What is simultaneous in one reference frame is not simultaneous in another.

The fact that you happen to be in two different places "at once" doesn't break any important principles; in fact there's no reason to believe that there's any unusual connection between the two sets of particles other than sharing a worldline.

Then what would an observer see as he watches John preparing to travel back in time, would he not see the time traveling John approaching the preparing John and both being anihilated when they come together?

alexi_drago
5th January 2012, 01:44 PM
Or once your delorean is going at 88 mph you started traveling back in time (say the same rate but in reverse), what is the position of the two sets 1ms after reaching 88mph (or 1ms before from the pre 88mph travelers frame)?

JFrankA
5th January 2012, 02:02 PM
I don't have time for this thread.

I will in the future. But in the past when I wrote that sentence it was true.

It may not be true now, but later it will be.

levi
5th January 2012, 03:21 PM
So the saying is true than why this response

Yes and no.

I am a little confused about yes and no?

Roboramma
5th January 2012, 04:57 PM
So the saying is true than why this response

I am a little confused about yes and no?

Say you keep two clocks with you at all times, and you keep them arbitrarily close together (so we can ignore tidal forces). They will always keep the same time*.

The same time measures the rates at which your bodily functions take place, the rates of chemical reactions, the rates at which your neurons fire, and how long it takes to boil a kettle.

So yes.

On the other hand, the ratio of your proper time to mine can change dramatically.

So no.

Thus, yes and no.

* Of course, these are ideal clocks, in the real world one might break or have some other mechanistic reason for not keeping correct time, but if they are accurately measuring your proper time, they will both keep the same time.

Roboramma
5th January 2012, 05:02 PM
How do you seperate from yourself? I mean you can travel through time at different rates due to velocity and gravity but there's only ever one of you and your atoms but when you start traveling backwards, at any time that the time traveling crosses there are two of you and all your atoms.

In this diagram you can see an electron move forward through time, hit a photon and "bounce" backward through time. You can notice how you thus have the same electron existing at two different places at the same time:

While it's not time travel in the sense of science fiction, it's pretty much exactly what you are saying is impossible.

alexi_drago
6th January 2012, 05:28 AM
In this diagram you can see an electron move forward through time, hit a photon and "bounce" backward through time. You can notice how you thus have the same electron existing at two different places at the same time:

While it's not time travel in the sense of science fiction, it's pretty much exactly what you are saying is impossible.

I'm not saying it's impossible, just that it's going to be really messy if a person tries it, for some amount of time the two sets of the time traveler are going to occupy roughly the same volume of space time and it's the same when the time traveler gets to when he/she's going and want's to come out of reverse.

ETA: just realised that if you make a single journey back in time then there will be three of you in existance between the points in time when your journey started and ended.

AvalonXQ
6th January 2012, 05:32 AM
I'm not saying it's impossible, just that it's going to be really messy if a person tries it, for some amount of time the two sets of the time traveler are going to occupy roughly the same volume of space time and it's the same when the time traveler gets to when he/she's going and want's to come out of reverse.

Again, it depends on how the time travel is occuring. This is not a problem if you're using a timelike curve or other spacetime bending for time travel -- you simply travel through space, and when you get to the other end you can pass yourself heading for the anomaly.

alexi_drago
6th January 2012, 05:41 AM
Again, it depends on how the time travel is occuring. This is not a problem if you're using a timelike curve or other spacetime bending for time travel -- you simply travel through space, and when you get to the other end you can pass yourself heading for the anomaly.

That had occurred to me but if you're meaning the spacetime is distorted so much that time turns back on itself then will the same thing not happen?

alexi_drago
6th January 2012, 05:56 AM
In this diagram you can see an electron move forward through time, hit a photon and "bounce" backward through time. You can notice how you thus have the same electron existing at two different places at the same time:

While it's not time travel in the sense of science fiction, it's pretty much exactly what you are saying is impossible.

The diagram doesn't show up but I looked it up, can that happen in reverse?

Roboramma
6th January 2012, 06:09 AM
The diagram doesn't show up but I looked it up, can that happen in reverse?

Sorry, not sure I understand the question: what would it mean for it to happen in reverse?
The description I gave says "this, then that", but that's somewhat sloppy language given that if you look at the arrow of time, both are happening at the same time.

alexi_drago
6th January 2012, 06:17 AM
Sorry, not sure I understand the question: what would it mean for it to happen in reverse?
The description I gave says "this, then that", but that's somewhat sloppy language given that if you look at the arrow of time, both are happening at the same time.

Can the arrow of time point the other way on the diagram?

MRC_Hans
6th January 2012, 06:22 AM

If was possible, would [impassibility #2] become possible?

Excuse me, but how the hell should be able to even guess about that? After all, what are your conditions for travelling to your past (quite apart from the nasty little problem of even [I]finding the Earth, as already mentioned)?

Will you be bodily present? Will you be your present self or your past self? Will your past self still be there, so you meet yourself? If you literally enter your past self, what happens to your present self? ... etc, etc.....

And even if the answer to those were entered into the scenario, it would all be wild guesswork. You cannot extrapolate known rules for that which does not comply with known rules, in the first place.

Hans :dio:

alexi_drago
6th January 2012, 08:04 AM
Sorry, not sure I understand the question: what would it mean for it to happen in reverse?
The description I gave says "this, then that", but that's somewhat sloppy language given that if you look at the arrow of time, both are happening at the same time.

What I was thinking is that say you have an electron and an event that results in an electron and a positron (like the diagram but with time pointing the other way), 1 second after that event the positron and the original electron annihilate each other (as in the diagram). Has the electron travelled back in time by 1 second?

Soapy Sam
6th January 2012, 08:56 AM

If was possible, would [impassibility #2] become possible?

Excuse me, but how the hell should be able to even guess about that? After all, what are your conditions for travelling to your past (quite apart from the nasty little problem of even [I]finding the Earth, as already mentioned)?

Will you be bodily present? Will you be your present self or your past self? Will your past self still be there, so you meet yourself? If you literally enter your past self, what happens to your present self? ... etc, etc.....

And even if the answer to those were entered into the scenario, it would all be wild guesswork. You cannot extrapolate known rules for that which does not comply with known rules, in the first place.

Hans :dio:
Maybe you can't in Denmark, but we have David Cameron in control, so fantasy comes easy.

Roboramma
6th January 2012, 04:43 PM
Can the arrow of time point the other way on the diagram?

Sure, as far as we know reversing time's arrow is no different from taking all the velocities of everything in the universe and multiplying by -1.

Which leads to some interesting questions. But, yes, the physics still works if you reverse the arrow of time.

In this case, instead of an electron-positron pair coming together and annihilating to form a photon, you've got a photon that becomes an electron-positron pair.

Regarding your second question, I always thought Feynman's idea (I think it didn't work out, but it could be true) that there is only one electron in the universe, bouncing back and forth through time, was pretty cool anyway. ;)

alexi_drago
6th January 2012, 05:25 PM
.......

Regarding your second question, I always thought Feynman's idea (I think it didn't work out, but it could be true) that there is only one electron in the universe, bouncing back and forth through time, was pretty cool anyway. ;)

If that was the case then where are all the positrons? and why is there a finite number of electrons?

Roboramma
7th January 2012, 04:09 AM
If that was the case then where are all the positrons? and why is there a finite number of electrons?

I at least understand the positron question, though don't have an answer off the top of my head. :boxedin:

Farsight
7th January 2012, 04:41 AM
Sure, as far as we know reversing time's arrow is no different from taking all the velocities of everything in the universe and multiplying by -1.There's no such thing as a negative velocity, Robo. Sure you can "define" some direction as a negative direction, but the moving object isn't travelling at -5mph. There's no such thing as a negative speed, and no such thing as a negatie length.

Which leads to some interesting questions. But, yes, the physics still works if you reverse the arrow of time.It's a metaphorical arrow derived from entropy, which is an emergent property of systems. There isn't some real arrow pointing in some real direction. It's another figure of speech, like "we travel forward in time at one second per second".

In this case, instead of an electron-positron pair coming together and annihilating to form a photon, you've got a photon that becomes an electron-positron pair.Conservation of momentum applies in electron-positron annihilation, so you get two photons. Or more. But not one. See wiki (http://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation#Low_energy_ case).

Regarding your second question, I always thought Feynman's idea (I think it didn't work out, but it could be true) that there is only one electron in the universe, bouncing back and forth through time, was pretty cool anyway.I'm a bit of a Feynman fan, but I think this was a really uncool idea. The positron is only a time-reversed electron in the sense that it has the opposite chirality. See this web page (http://www.quantumdiaries.org/2011/06/19/helicity-chirality-mass-and-the-higgs/) for a bit about chirality. To get a handle on it, see this depiction (http://members.optushome.com.au/walshjj/toroid2.jpg) of an electron from the Williamson / van der Mark model, and reverse the direction of the arrowheads.

Roboramma
7th January 2012, 04:55 AM
There's no such thing as a negative velocity, Robo. Sure you can "define" some direction as a negative direction, but the moving object isn't travelling at -5mph. There's no such thing as a negative speed, and no such thing as a negatie length.

Sure there is: - 5m up = 5m down. I don't see what's wrong with that. The math certainly works out.

But it doesn't really matter anyway. You certainly accept that there is such a thing as traveling in the opposite direction with the same speed, yes?

It's a metaphorical arrow derived from entropy, which is an emergent property of systems. There isn't some real arrow pointing in some real direction. It's another figure of speech, like "we travel forward in time at one second per second". I'm aware of that. The question is "if you reverse the velocities, what happens?" And you'll find that it's exactly what you'd see if you'd filmed those events and ran that film in reverse.

I don't see where you think I said "there's a real arrow pointing in some real direction".

Conservation of momentum applies in electron-positron annihilation, so you get two photons. Or more. But not one. See wiki (http://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation#Low_energy_ case). Thanks for the correction, if I'd thought about it for a second I should have realised that. :o

I'm a bit of a Feynman fan, but I think this was a really uncool idea. Um, okay. To each his own, I find it interesting myself.

alexi_drago
7th January 2012, 05:21 AM
If that was the case then where are all the positrons? and why is there a finite number of electrons?

I at least understand the positron question, though don't have an answer off the top of my head. :boxedin:

If there were conditions at the beginning and end of time to cause the bounce of the single electron for the first to the nth time why would it stop at n?

Farsight
7th January 2012, 05:35 AM
Sure there is: - 5m up = 5m down. I don't see what's wrong with that. The math certainly works out. But it doesn't really matter anyway. You certainly accept that there is such a thing as traveling in the opposite direction with the same speed, yes?Sure no problem. But it's still motion rather than negative motion.

I'm aware of that. The question is "if you reverse the velocities, what happens?" And you'll find that it's exactly what you'd see if you'd filmed those events and ran that film in reverse.If you started with a container of gas, where all the molecules were initially in one corner, they fill the container almost instantly, because they're moving at about 500m/s. Then they're rattling around in the container bumping into one another. Because of that, if you then had some magic button that could reverse all their velocities, they wouldn't all end up neatly in the corner where they started out. Or should I say the chance of that happening is extremely slim. The arrow of time is something like the "direction" between the initial order and the eventual chaos.

I don't see where you think I said "there's a real arrow pointing in some real direction".Sorry, you didn't. But IMHO people do seem to think about it as if it's something real.

Thanks for the correction, if I'd thought about it for a second I should have realised that.My pleasure.

Um, okay. To each his own, I find it interesting myself.Fair enough. I guess time travel is my pet hate. See what I said in post #14 (http://forums.randi.org/showpost.php?p=7899372&postcount=14).

Roboramma
7th January 2012, 06:26 AM
If you started with a container of gas, where all the molecules were initially in one corner, they fill the container almost instantly, because they're moving at about 500m/s. Then they're rattling around in the container bumping into one another. Because of that, if you then had some magic button that could reverse all their velocities, they wouldn't all end up neatly in the corner where they started out. Or should I say the chance of that happening is extremely slim. That's actually an interesting question that I was thinking about the other day: in a newtonian style clockwork, determinist universe, they would end up neatly in that corner.

But given quantum mechanics and indeterminacy, perhaps not. I assume that's what you mean?

Roboramma
7th January 2012, 06:29 AM
Regarding your post #14 I'm intrigued by it, but not sure I can agree. Certainly we model time as a dimension. And while it's inextricable from motion, the same can be said in reverse: motion is meaningless without space-time.

But that said, the book you mentioned sounds interesting. :)

Farsight
7th January 2012, 09:53 AM
That's actually an interesting question that I was thinking about the other day: in a newtonian style clockwork, determinist universe, they would end up neatly in that corner. But given quantum mechanics and indeterminacy, perhaps not. I assume that's what you mean?Not really. I was thinking of bog-standard entropy (http://en.wikipedia.org/wiki/Entropy).

Regarding your post #14 I'm intrigued by it, but not sure I can agree. Certainly we model time as a dimension. And while it's inextricable from motion, the same can be said in reverse: motion is meaningless without space-time.The thing is, you can hold your hands up a foot apart and see that there's a gap between them. So you can kind of "see" space. And you can waggle your hands, so you can see motion. But you can't see any time flowing. So you put motion above time in the pecking order. Note that you can't actually see space-time either. Things don't move through it you know. It's an "all time view" of space and motion through it. A mathematical space, not actual space. The space around the Earth isn't curved, motion through it is curved.

But that said, the book you mentioned sounds interesting.It is. It's heavy going at times, but it's a bit of an eye-opener. Once you get the hang of this motion thing you wonder why you ever entertained the possibility of time travel.

RobDegraves
7th January 2012, 10:32 AM
Well...

I suppose this statement by MRC-Hans is closest to my opinion...

You cannot extrapolate known rules for that which does not comply with known rules, in the first place.

Time travel is currently being debated by a number of luminaries in the physics field. To say that there is not a consensus is an understatement.

This statement by Farsight however...

Sorry to spoil anybody's fun here, but backward time travel is impossible because we don't even travel forward in time. It's just a figure of speech.

is a bit arrogant considering that time is considered a real consideration by modern physics.

I'm quite interested in the physics of time in general but from the extensive reading I have done so far on the subject, the best statement that I can make on the subject of time travel is...

We don't know yet.

Farsight
7th January 2012, 11:10 AM
Rob: my views on this stem from A World Without Time: The Forgotten Legacy of Godel and Einstein (http://www.amazon.co.uk/World-Without-Time-Forgotten-Einstein/dp/0713993871). Plus other reading, and thinking about it, and talking to lots of people. The blurb for this book maybe gives you the impression that "time does not exist", but that isn't accurate. It doesn't exist as something that flows or as something we actually move through.

Unfortunately there are some celebrity physicists out there who rather trade on the possibility of time travel, and talk it up. It's the sort of thing that gets them publicity and sells books. People rather like the notion of time travel, and so do the media. If ninety-nine physicists said time travel was impossible, and one physicist said it was possible, guess which one will feature in the newspaper.

RobDegraves
7th January 2012, 02:31 PM
If ninety-nine physicists said time travel was impossible, and one physicist said it was possible, guess which one will feature in the newspaper.

Except that it's not a question of popularity, it's a matter of proof.. of which there is little at this time.

Time is generally understood as a dimension, like height or width. Dimension are a way to understand position but also have a real existence. Though it is a complex subject the basics are fairly similar. Time dilation is a well measured phenomenon and there are some solutions to specific time dilation problems that resemble time travel a great deal.

Basically, I disagree with your statement that you know exactly what time is and how it works in all circumstances. I'm pretty sure a lot of physicists would also disagree.

AvalonXQ
7th January 2012, 03:52 PM
The thing is, you can hold your hands up a foot apart and see that there's a gap between them. So you can kind of "see" space. And you can waggle your hands, so you can see motion. But you can't see any time flowing.

I disagree. All of these things, time included, are observed in the above example.
We can observe objects at two different locations and define this difference in property as "position".
We can observe objects at two different moments and define this difference in property as "time".
We can observe a change from one position to another, and define this change as a "distance".
We can observe a change from one time to another, and define this change as a "duration".
We can then define "movement" as a change in "distance" over a "duration".

Movement is not fundamental; it is recording a change in property. Movement occurs over both distance and time, and requires both to be understood.

You can only understand space or time, either one, by understanding a relational difference between two different values of the thing you're trying to understand; in other words, our understanding of either space or time is relational. One is not more fundamental or observable than the other; space is meaningless without two positions, and time without two instants. But we observe both, and can therefore understand both.

Farsight
8th January 2012, 06:52 AM
Except that it's not a question of popularity, it's a matter of proof.. of which there is little at this time.There's none. None whatsoever. And there's no proof of angels either.

Time is generally understood as a dimension, like height or width. Dimension are a way to understand position but also have a real existence. Though it is a complex subject the basics are fairly similar.It isn't complicated at all, it's pretty obvious. You can move in space. You can jump back a metre. Or forward. That's real enough. But you can't do this with time. You can't jump backwards a second, or forwards. Because it's a dimension in the sense of measure, not in the sense of freedom of motion. And what's being measured? All you have to do to work this out is look at a clock. Be it a pendulum clock, a spring-driven clock, a quartz clock, or an atomic clock, clocks don't actually measure "the flow of time". They all clock up some kind of regular cyclic motion, and show you some kind of cumulative display that you call the time. The mechanism of a clock isn't call a motion for nothing.

Time dilation is a well measured phenomenon and there are some solutions to specific time dilation problems that resemble time travel a great deal.All that happens in time dilation is that the motion local to a clock occurs at a reduced rate because the clock is moving fast. The simple inference of time dilation due to relative velocity (http://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_du e_to_relative_velocity) is a case in point. The Lorentz factor is derived from Pythagoras's theorem. If you're my twin and you take a fast out and back trip, you come back with fewer grey hairs. No problem there. You've experienced less time than me. But it isn't some form of time travel. When you come back you don't come back to the middle of last week.

Basically, I disagree with your statement that you know exactly what time is and how it works in all circumstances.Let me explain it, think it through, and you'll find that what I'm saying is very simple, and there's nothing wrong with what I'm saying. Then perhaps you'll modify your view. Maybe. The thing is, people like the idea of time travel, and they've liked it for years. All too often they don't like some guy like me saying why it's science fiction.

I'm pretty sure a lot of physicists would also disagree.Like I said before, some celebrity physicists trade on woo like time travel. It gets their name in the papers, and it sells books. I'd say most physicists do not concur with the possibility of time travel, and if there was some kind of contest between me and say Ron Mallett (http://en.wikipedia.org/wiki/Ronald_Mallett), they'd side with me.

Farsight
8th January 2012, 07:12 AM
I disagree. All of these things, time included, are observed in the above example.You can't actually observe time. You can observe the space between your hands, and you can observe your hands moving, but you can't observe time. Really.

We can observe objects at two different locations and define this difference in property as "position".No problem with position.

We can observe objects at two different moments and define this difference in property as "time".That you can. But if there wasn't any motion at all, including in your brain, and if light wasn't moving either, how can you distinguish one moment from another? You can't. Think about some science fiction movie you've seen where somebody can "stop time". What they actually stop is motion.

]We can observe a change from one position to another, and define this change as a "distance".OK.

We can observe a change from one time to another, and define this change as a "duration".No problem.

We can then define "movement" as a change in "distance" over a "duration".You can. But remember what I said. You can observe the space between your hands, and you can observe your hands moving. You can see motion happening. You can observe motion. But you can't observe time. So you shouldn't define motion, which you can see, in terms of something you can't.

Movement is not fundamental; it is recording a change in property. Movement occurs over both distance and time, and requires both to be understood.Sorry Avalon, but that's wrong. Movement happens. You can see it. It's more fundamental than time.

You can only understand space or time, either one, by understanding a relational difference between two different values of the thing you're trying to understand; in other words, our understanding of either space or time is relational. One is not more fundamental or observable than the other; space is meaningless without two positions, and time without two instants. But we observe both, and can therefore understand both.Again, what you can observe is space and motion. And when you appreciate that clocks clock up motion, you can understand both space and time. And then you can understand why time travel is science fiction.

AvalonXQ
8th January 2012, 09:41 AM
You can't actually observe time. You can observe the space between your hands, and you can observe your hands moving, but you can't observe time. Really.

You can observe time. You can observe the duration between two events, and waiting between them.

You can observe time. Really.

AvalonXQ
8th January 2012, 09:42 AM
That you can. But if there wasn't any motion at all, including in your brain, and if light wasn't moving either, how can you distinguish one moment from another? You can't.

If there wasn't any motion at all, including your brain, and if light wasn't moving either, how can you distinguish one position from another? You can't.

AvalonXQ
8th January 2012, 09:45 AM
You can. But remember what I said. You can observe the space between your hands, and you can observe your hands moving. You can see motion happening. You can observe motion.

No, you can't. You can observe an object in a position at a time, and then you can observe what you have decided is the same object in a different position at a different time. You call this "motion", but what you're really observing is a change in position and time. It's position and time you're observing; "motion" is just what you call it when these things change.

Describe motion without either position or time. Explain how you could perceive motion without being able to observe either position or time.

dafydd
8th January 2012, 02:41 PM
I once saw a time machine with a sign hanging on it. 'Out of order, come back yesterday.'

JoeTheJuggler
8th January 2012, 02:52 PM
would the saying you only have certain amount time alive be true?

What saying?

(By "certain amount" do you merely mean "finite amount"? I don't think most people believe the amount of time you will be alive is predetermined.)

levi
8th January 2012, 08:12 PM
yes I mean finite amount. By finite "I mean Existing, persisting, or enduring for a limited time only; impermanent."
http://www.thefreedictionary.com/finite

For example we can only last so long because we age. Even if time travel is somehow possible.

And your other question know one knows if everything is predetermined or not. Even not taking into consideration time travel. I could be wrong about the predetermined stuff but really don't want to debate it because I don't know that much about the subject.

JoeTheJuggler
8th January 2012, 08:40 PM
yes I mean finite amount. By finite "I mean Existing, persisting, or enduring for a limited time only; impermanent."
http://www.thefreedictionary.com/finite
Yeah, I'm familiar with the word. It doesn't mean the same thing as "certain", and I'm still not familiar with the saying you referred to.

For example we can only last so long because we age. Even if time travel is somehow possible.

How would time travel to the past change the duration of your life?

By definition, if you travelled into a past time, you would still subjectively be experiencing that passage of time as "new" time in your lifespan. You would still age and eventually die. How would time travel make your lifespan infinite?

It sounds maybe like you're not talking about time-travel the way that term is usually used, but more as something like Billy Pilgrim's becoming unstuck in time. He merely experienced his life time in a jumbled up sequence, but any time he went back to the time when he was a child, he was still a child, and when he went to the time when he was 25, he was 25. His life was still finite too.

L.Y.S.
8th January 2012, 11:54 PM
delete lol

Farsight
9th January 2012, 03:17 AM
You can observe time. You can observe the duration between two events, and waiting between them. You can observe time. Really.You aren't really observing time. Yes, you can see two events, no problem with that. Let's call them event A and event B. You see event A, then a whole load of other events occur in your brain and elsewhere which you use to determine duration, then you see event B. Did you read my post #14 (http://forums.randi.org/showpost.php?p=7899372&postcount=14) about the stasis box? Suppose you see event A just as I close the door, then I open the door and you see event B. These two events could be separated by a duration of five years as far as everybody else is concerned, but to you they're seemingly separated by a second, because you haven't experienced any intervening events. And for those events to happen, things have to move.

If there wasn't any motion at all, including your brain, and if light wasn't moving either, how can you distinguish one position from another? You can't.Agreed. We use the motion of light to define both the second and the metre.

No, you can't. You can observe an object in a position at a time, and then you can observe what you have decided is the same object in a different position at a different time. You call this "motion", but what you're really observing is a change in position and time. It's position and time you're observing; "motion" is just what you call it when these things change. Describe motion without either position or time. Explain how you could perceive motion without being able to observe either position or time.You perceive motion, that's just what you do. And your perception relies on light moving to your eye, and then nerve impulses moving around your brain. You see the moving object, you say that's it's position now, and label that as event A. Then you tot up intervening events associated with other motion including what's going on in your head, and then you say that's it's position now, and label it as event B. You can see that the object changed its position in space - it was over on the left now it's over on the right. You really can observe a change in position. But you aren't actually observing time here. You can't see time flowing like some river. You can't see the object "moving through time" like it moves through space. And that duration between events A and B is something you determine from all the other things moving. Like your clock. People say a clock "measures the flow of time", but all clocks really do, is clock up some kind of regular motion and display a cumulative total that we then call the time.

AvalonXQ
9th January 2012, 06:34 AM
You aren't really observing time. Yes, you can see two events, no problem with that. Let's call them event A and event B. You see event A, then a whole load of other events occur in your brain and elsewhere which you use to determine duration, then you see event B. Did you read my post #14 (http://forums.randi.org/showpost.php?p=7899372&postcount=14) about the stasis box?
The problem is that the stasis box is a fiction; in fact, if you put me in a box, I would continue to experience the intervening time. I would, in fact, know that time has passed between the two events.
And, again, a similar statement can be made about space. I can create a hypothetical "inertial dampening" box where you don't experience acceleration. I can then show you an object, close the box, move you a million miles, and show you another object in the same position.

Distance and time are in the same situation; they are both relational, and we experience a "gap" between them only by noting that something could be there but isn't.

You perceive motion, that's just what you do. And your perception relies on light moving to your eye, and then nerve impulses moving around your brain. You see the moving object, you say that's it's position now, and label that as event A.
I bolded and underlined the important word there.

Then you tot up intervening events associated with other motion including what's going on in your head, and then you say that's it's position now, and label it as event B. You can see that the object changed its position in space - it was over on the left now it's over on the right.
And there we have it again. Even in your own description of motion, you note that it is a change in time as well as a change in space.
We observe events, and therefore perceive both space and time for those events. When we observe changes in space and time, we call that "motion", but motion derives from our classification of events by distance and duration. It does not preceed those ideas.

The fact that it's a change in time (from "then" to "now") is just as important as the change in space (from "here" to "there"). And we know this because a change in space without a change in time is not perceived as motion.

Example: I show you a picture. There is an image of an apple on the left. The exact same image is shown on the right. Do you detect motion? You don't, even though there's a difference in position between the left and the right, because there's no change in time. You perceive it as two distinct objects because both exist at the same time.

Farsight
12th January 2012, 04:40 AM
Sorry to be slow in replying, Avalon. A lot of other stuff pushed this down the list and I missed it.

The problem is that the stasis box is a fiction; in fact, if you put me in a box, I would continue to experience the intervening time. I would, in fact, know that time has passed between the two events.Not if you were frozen. The stasis box is just an idealised freezer. We can freeze embryos now, imagine we could freeze an adult. You're strapped down with intravaneous tubes, I press a button and ask you to count backwards from a hundred, you get to about 93, then the next thing you now I'm standing in the doorway saying welcome to the future.

And, again, a similar statement can be made about space. I can create a hypothetical "inertial dampening" box where you don't experience acceleration. I can then show you an object, close the box, move you a million miles, and show you another object in the same position.No problem with that. Somebody in freefall doesn't feel any inertia. You could place me in my box, and the object, in space with no orbital velocity, let us fall towards the sun for a while, then open the box once we've fallen a million miles.

Distance and time are in the same situation; they are both relational, and we experience a "gap" between them only by noting that something could be there but isn't.There's still a big difference between space and time. You travel through space by moving, but you "travel through time" by not moving at the cellular or atomic level whilst everything else does.

I bolded and underlined the important word there.I underlined the word "now" second time round to get across that it's an important word.

And there we have it again. Even in your own description of motion, you note that it is a change in time as well as a change in space.And that change in time is the result of motion. Like I said, what clocks do is "clock up" some kind of regular motion and display a cumulative total that we then call the time. There's motion going on in our heads too, and all around us, and when you track it back through relativity, it's comes down to the motion of light. Without it we couldn't think, clocks wouldn't tick, and there wouldn't be any time. Like in that stasis box.

We observe events, and therefore perceive both space and time for those events. When we observe changes in space and time, we call that "motion", but motion derives from our classification of events by distance and duration. It does not preceed those ideas.Yes it does. The simplified idealised clock used in relativity is the parallel-mirror light clock. There's no travelling through time there, it's just light moving through space.

The fact that it's a change in time (from "then" to "now") is just as important as the change in space (from "here" to "there"). And we know this because a change in space without a change in time is not perceived as motion.That doesn't happen. When things change their position, it's because they move.

Example: I show you a picture. There is an image of an apple on the left. The exact same image is shown on the right. Do you detect motion? You don't, even though there's a difference in position between the left and the right, because there's no change in time. You perceive it as two distinct objects because both exist at the same time.You're showing me a still picture of two apples, that's all. There's no motion in this picture, so there's no time in it. I can see the gap between the two apples, so there's space in this picture, but there isn't any time.

Look at what clocks actually do, and maybe you'll appreciate all this. They don't actually measure the flow of time, they just clock up some kind of motion. Be it a pendulum clock, a spring-driven mechanical clock, a quartz wristwatch, or a light clock, there's always something moving, and the gizzards of a clock aren't called a motion for nothing. Things move, we clock up that motion and call it the time, but things don't actually move through time, or travel through time at all. We don't really travel forward through time, so travelling backwards in time is a dead duck.

Complexity
12th January 2012, 10:22 AM
I am a little confused about yes and no?

Yes

and no.

Roboramma
12th January 2012, 02:54 PM
There's still a big difference between space and time. You travel through space by moving, but you "travel through time" by not moving at the cellular or atomic level whilst everything else does.

I don't see how it's all that different: if I put you in the "stasis box" and move the box to the other side of the galaxy, then open it, voila, you'll have travelled to the other side of the galaxy.

In this sense your stasis box is more like a teleportation machine than anything else: you can step in at one point in spacetime and step out at another without having to experience crossing the intervening spacetime.

Anyway, regarding time as a dimension: your viewpoint is interesting to me in so much as time and motion are intricately connected. But it doesn't change any of the facts on the ground: we have a model (say relativity) that treats time as one dimension of spacetime. That model works. It has enormous predictive power. And nothing you've said shows any fundamental errors in the model.

If we want to think about time differently, it seems to me that you are offering another viewpoint that could potentially lead to some interesting results. But we have no reason to discard the current model in which time is treated as a dimension, and I find the way that you post "time is not a dimension" misleading as those who don't know better will assume that you speak for physics in general and not from a perspective of "it may be possible to look at physics from a different perspective which focuses on motion, though it's far from the consensus opinion".

I also have to agree with others that if time is "not a dimension" then the same arguments apply to space. We measure time with a clock, we measure space with a ruler. Motion is involved in both of these things.

Anyway, if time isn't a dimension, it'd odd that we can treat it as though it were mathematically.

Farsight
13th January 2012, 07:13 AM
I don't see how it's all that different: if I put you in the "stasis box" and move the box to the other side of the galaxy, then open it, voila, you'll have travelled to the other side of the galaxy. In this sense your stasis box is more like a teleportation machine than anything else: you can step in at one point in spacetime and step out at another without having to experience crossing the intervening spacetime.It isn't like a teleportation machine at all, Robo. You've still got to lug it around. It's just a glorified refrigerator. I don't experience any motion at all inside it, just as I wouldn't if it was a plain old box and you somehow managed to get it moving at c. There can't be any motion inside a box moving at c because when you add the internal motion to the external motion the result would exceed c. In fact, that's why you can't move matter at c.

Anyway, regarding time as a dimension: your viewpoint is interesting to me in so much as time and motion are intricately connected. But it doesn't change any of the facts on the ground: we have a model (say relativity) that treats time as one dimension of spacetime. That model works. It has enormous predictive power. And nothing you've said shows any fundamental errors in the model.There aren't any errors in the model, the errors are in what people say the model tells you. Don't think I'm challenging special relativity here, I come out with this stuff because Einstein did. And Godel. People will tell you that he found a possible way to do time travel with a rotating universe, but that's b*llocks. He concluded exactly the opposite, saying time cannot pass if you can visit the past. The errors only start creeping in with with closed timelike curves, where non-real solutions appear. A non-real solution is a bit like saying you can cover the floor of a 16mē room with a carpet measuring -4m by -4m.

If we want to think about time differently, it seems to me that you are offering another viewpoint that could potentially lead to some interesting results. But we have no reason to discard the current model in which time is treated as a dimension, and I find the way that you post "time is not a dimension" misleading as those who don't know better will assume that you speak for physics in general and not from a perspective of "it may be possible to look at physics from a different perspective which focuses on motion, though it's far from the consensus opinion".I said time is a dimension in the sense of measure rather than in the sense of freedom of motion. See post #76 (http://forums.randi.org/showpost.php?p=7914600&postcount=76). You can jump back a metre but not a second. You still treat it as a dimension, but not exactly like the space dimensions. So you say we have 3+1 dimensions rather than 4.

I also have to agree with others that if time is "not a dimension" then the same arguments apply to space. We measure time with a clock, we measure space with a ruler. Motion is involved in both of these things.It isn't quite the same. Think about that picture that Avalon described. It's a still picture of two apples. There's no time in this picture, and no motion, but you can see the space between the apples.

Anyway, if time isn't a dimension, it'd odd that we can treat it as though it were mathematically.It isn't odd at all once you see how it works. Suppose I throw an apple across the room in front of you. You can see it, and you can see it moving. Suppose you filmed it, then cut the film up into individual frames and stacked them up on top of one another. You've now got a little block representing spacetime, and if you look closely you can see a red/green streak in there. That's like the worldline of the apple. You can apply mathematics to this and everything works because it accurately reflects what actually happens in the real world. Note though that the apple moves through the space of the room, but it's just a motionless streak in the block. There's no actual motion in or through spacetime, because it's an "all times view". It's all pretty simple once you get the hang of it.