How did we get so far away so fast?

boyntonstu · 19th October 2009, 07:54 AM

How did we get so far away so fast?

If we can see light from stars that originated billions of years ago,
and everything started from a single point, how did we get so far away
so quickly?

IOW If we are 10 billion light years from an object, did we separate
faster than the speed of light?

Seren_ · 19th October 2009, 07:57 AM

From what I understood, the Universe is expanding, and while some galaxies are drifting apart (and some other are getting closer), the biggest contribution to the huge distance is that the empty space inbetween has "grown".

This is the usual image of ants walking on an inflattable balloon. While they are moving slowly, since the balloon is getting bigger there are further and further apart.

dlorde · 19th October 2009, 08:07 AM

Originally Posted by boyntonstu

If we can see light from stars that originated billions of years ago, and everything started from a single point, how did we get so far away so quickly?

IOW If we are 10 billion light years from an object, did we separate
faster than the speed of light?

The universe is currently estimated to be almost 14 billion years old. The idea is that stuff has been expanding from that point for 14 billion years, and, as space itself expands, the most distant parts may be moving away at > c.

boyntonstu · 19th October 2009, 08:16 AM

Originally Posted by dlorde

The universe is currently estimated to be almost 14 billion years old. The idea is that stuff has been expanding from that point for 14 billion years, and, as space itself expands, the most distant parts may be moving away at > c.

> c is supposed to be impossible.

I don't understand the claim that we are viewing light from the beginning of the Universe.

If is light from the beginning that is being observed, wasn't our sun there at the same time?

RecoveringYuppy · 19th October 2009, 08:18 AM

Originally Posted by boyntonstu

IOW If we are 10 billion light years from an object, did we separate
faster than the speed of light?

There's been more than 10 billion years since the big bang, so we wouldn't need to separate faster than light to do that. But, as has already been said, there are presumably galaxies beyond the distance we can see. And some day the expansion of the universe is going to have taken the galaxies that we can see "over the edge" to where we can't see them any longer.

steenkh · 19th October 2009, 08:24 AM

Originally Posted by boyntonstu

I don't understand the claim that we are viewing light from the beginning of the Universe.

No. We are not seeing light from the beginning of the universe. The oldest light we can see is the Cosmic Microwave Background, which was radiated when the universe cooled sufficiently to become transparent to light, about 379,000 years after the Big Bang.

Quote:

If is light from the beginning that is being observed, wasn't our sun there at the same time?

As you see, the atoms that make up our Sun had already moved 379,000 years by the time the CMB broke free. The light from distant galaxies is much, much younger even.

Roboramma · 19th October 2009, 08:25 AM

Originally Posted by boyntonstu

> c is supposed to be impossible.

It's impossible for things to move through space faster than c. However, if the space between two objects is moving, they can be carried away from each other faster than c, in which case they will be forever lost from view.

Edit: That said, remember that while there are regions that are very far away, the universe is also very old.

H3LL · 19th October 2009, 08:31 AM

I though light had no "age". Surely there is no such thing as "young" light or "old" light.

The source of the light? Well that's OK.

Dancing David · 19th October 2009, 08:31 AM

Originally Posted by boyntonstu

How did we get so far away so fast?

If we can see light from stars that originated billions of years ago,
and everything started from a single point, how did we get so far away
so quickly?

IOW If we are 10 billion light years from an object, did we separate
faster than the speed of light?

Space itslef is expanding according to theory. At a certain pase there was a very fast expansion called 'inflation'.
And no it did not inflate faster than the speed of light. (At least that is my understanding, because the speed of light is within space.)

aggle-rithm · 19th October 2009, 08:34 AM

Originally Posted by Roboramma

It's impossible for things to move through space faster than c. However, if the space between two objects is moving, they can be carried away from each other faster than c, in which case they will be forever lost from view.

This is the basis for the warp drive theory. Although matter cannot be accellerated to the speed of light, there is nothing to prevent space from moving at the speed of light or faster. So, theoretically, if we can get a region of space that contains a spaceship in it to move faster then light, the ship will go along for the ride.

The two problems are: Finding a HUGE energy source to warp the space around a ship (bigger than the lifetime output of a star, probably) and finding a way to propel that warp bubble to any speed, much less faster-than-light speeds.

aggle-rithm · 19th October 2009, 08:36 AM

Originally Posted by Dancing David

Space itslef is expanding according to theory. At a certain pase there was a very fast expansion called 'inflation'.
And no it did not inflate faster than the speed of light. (At least that is my understanding, because the speed of light is within space.)

If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light.

steenkh · 19th October 2009, 08:36 AM

Originally Posted by H3LL

I though light had no "age". Surely there is no such thing as "young" light or "old" light.

Though light does not age, it still makes sense to speak about light emitted a long time ago as "older" than light emitted a short while ago.

JHGRedekop · 19th October 2009, 08:39 AM

Originally Posted by boyntonstu

> c is supposed to be impossible.

It's impossible to move through space at > c, but it is not impossible for space to expand at a rate such that, between two points sufficiently far apart, the net expansion of space between them exceeds c. The difference is subtle, but important.

Originally Posted by boyntonstu

I don't understand the claim that we are viewing light from the beginning of the Universe.

If is light from the beginning that is being observed, wasn't our sun there at the same time?

No. Our sun is less than five billion years old, while the universe is over 13 billion years old.

steenkh · 19th October 2009, 08:39 AM

Originally Posted by aggle-rithm

If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light.

Should that not read "red-shifted"?

lomiller · 19th October 2009, 08:58 AM

While I’m not exactly an expert on this, my understanding is that it isn’t correct to say the universe is expanding from a single point. A closer analogy is that the point the universe occupied at the big bang is itself expanding. That’s only my way of understanding it so it’s probably a deficient explanation in any number of ways.

JoeTheJuggler · 19th October 2009, 09:03 AM

Originally Posted by boyntonstu

How did we get so far away so fast?

So far away from what? You could as well consider stuff that is at the limits of our ability to see (c. 14 billion light years) and beyond to have gotten far away from us rather than us to have gotten far away from it.

There is no center or edge--just expansion. And it's been going on for nearly 14 billion years. So. . how fast is "so fast"?

JoeTheJuggler · 19th October 2009, 09:12 AM

Originally Posted by boyntonstu

> c is supposed to be impossible.

Says who?

While we can't travel or send information faster than the speed of light, we can observe velocities faster than the speed of light.

If we used the Earth as a fixed frame of reference, then the rest of the universe is indeed moving faster than the speed of light.

Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light.

Relativity does not claim that speeds faster than light are impossible in all cases.

Depending on what you mean, it is certainly possible for the universe to expand faster than the speed of light.

JoeTheJuggler · 19th October 2009, 09:21 AM

Originally Posted by JoeTheJuggler

Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light.

Maybe a simpler way of thinking of this.

You're at a fixed position and you shine a beam of light directly in front of you and another one exactly 180° away from it (directly behind you). The photons traveling away from you in front have a velocity of +1c and the photons traveling away from you behind have a velocity of -1c. From your perspective, they have a relative velocity of 2c to each other.

However, if you were riding on one of the photons, when you calculate your velocity relative to the photons going the opposite direction, you'd come up with a relative speed of 1c.

JoeTheJuggler · 19th October 2009, 09:30 AM

Originally Posted by boyntonstu

I don't understand the claim that we are viewing light from the beginning of the Universe.

If is light from the beginning that is being observed, wasn't our sun there at the same time?

No. The Big Bang was nearly 14 billion years ago. The Sun is only about 4.6 billion years old.

soylent · 19th October 2009, 11:05 AM

Originally Posted by steenkh

Should that not read "red-shifted"?

Yes, hence cosmic microwave background rather than cosmic x-ray background.

Ziggurat · 19th October 2009, 11:23 AM

Originally Posted by boyntonstu

I don't understand the claim that we are viewing light from the beginning of the Universe.

We aren't. The very early universe was opaque, so any light emitted during that very early period was absorbed, and no longer exists. It wasn't until around 300,000 years after the big bang that the universe became mostly transparent, and that is when the thermal background radiation of the universe originated. That background (which has cooled down with the expansion of the universe) is now known as the cosmic microwave background (CMB), and it is the oldest light we can see, and the oldest light we ever will be able to see. But it is NOT as old as the universe itself.

Stars and galaxies didn't form until sometime after the universe became transparent, so there's actually a gap in time between the CMB and the oldest stars and galaxies.

Eyeron · 19th October 2009, 11:40 AM

Okay, I'm confused, I've never heard that the universe is transparent. What exactly does that mean?

Paul C. Anagnostopoulos · 19th October 2009, 11:53 AM

Originally Posted by Eyeron

Okay, I'm confused, I've never heard that the universe is transparent. What exactly does that mean?

It means that you can see through it. Prior to 300,000 BB, you couldn't see through the dense stuff making up the universe because photons couldn't travel more or less freely. Not that you were around then, of course.

http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang

~~ Paul

MervinFerd · 19th October 2009, 12:09 PM

Originally Posted by Paul C. Anagnostopoulos

It means that you can see through it. Prior to 300,000 BB, you couldn't see through the dense stuff making up the universe because photons couldn't travel more or less freely. Not that you were around then, of course.
~~ Paul

That's probably a GOOD thing.

aggle-rithm · 20th October 2009, 06:52 AM

Originally Posted by steenkh

Should that not read "red-shifted"?

That's what I was wondering as I typed it.

Corsair 115 · 20th October 2009, 01:20 PM

Folks may want to check out the following program which aired on TVO a couple of weeks back. It was a lecture given by Lawrence Krauss, a professor in the Department of Physics at Arizona State University. The lecture, entitled Life, the Universe and Nothing, touched upon some of the subjects mentioned in this thread. I personally found it quite interesting.

I can't say if the link and its video will work for non-Canadians, but I'll post it anyway:

Lawrence Krauss on dark energy and the end of the universe

sol invictus · 20th October 2009, 01:28 PM

Originally Posted by boyntonstu

> c is supposed to be impossible.

I don't understand the claim that we are viewing light from the beginning of the Universe.

If is light from the beginning that is being observed, wasn't our sun there at the same time?

You know how at a fireworks display, you hear the explosions a second or so after they happen? The sounds you hear at any given moment are always a combination of sounds emitted nearby right then, sounds emitted 1 second earlier from something 343 meters away, sounds emitted 2 seconds earlier 686 meters away, everything in between, etc. So you're always hearing a continuum of "old" and "new" sound (you don't normally notice this, since sounds from far away are rarely loud enough to hear).

The same goes for light. The sun is nearby, so the light you're seeing from it now is only about 8 minutes old (it was emitted 8 minutes ago). The light we see from Alpha Centauri, the nearest star to the sun, was emitted about 4.4 years ago. The further you look, the older the light is, and so if there was nothing in the way you could see all the way back to the beginning in the universe by looking at light coming from really distant sources.

But as Zig pointed out, there is something in the way - the universe was opaque to light up to about 300,000 years, so that's as far back as we can see directly. The "light" from that time is called cosmic microwave background radiation.

JoeTheJuggler · 20th October 2009, 01:42 PM

Originally Posted by sol invictus

But as Zig pointed out, there is something in the way - the universe was opaque to light up to about 300,000 years, so that's as far back as we can see directly.

I don't think that's what limits how much of the universe we can see. That is, we know the universe is larger than what we can see of it. We can only see out (or back in time) as long as there has been time for that light to reach us. So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.)

Ziggurat · 20th October 2009, 01:59 PM

Originally Posted by JoeTheJuggler

I don't think that's what limits how much of the universe we can see. That is, we know the universe is larger than what we can see of it. We can only see out (or back in time) as long as there has been time for that light to reach us.

Yes, but the relevant time limit is set by when the universe became transparent, not by when the universe began, so that does indeed limit how much of the universe we can see.

Quote:

So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.)

I don't see what point you're trying to make. We see that opaque barrier (that's what the CMB is), so we definitely are running up against that limit. And since the universe went from opaque to transparent everywhere, the distinction between size, distance, and age issue isn't relevant. Perhaps you are confusing this limit with the oldest stars we can see (which are not as far away or as old as this opaque boundary), but that's a different issue.

ponderingturtle · 20th October 2009, 02:02 PM

Originally Posted by boyntonstu

> c is supposed to be impossible.

Speeds greater than C are imposible, what this is a rate in increase of the distance between to points increaseing with time.

That might seem like the same thing but it is only if you view space itself as fixed and not expanding. See the ants on the balloon analogy. They are walking away from each other at a certain speed, but that speed can be increased if you inflate the baloon at the same time. Relative to the baloon each of them is moving at the ant speed but the distance between them is increaseing at greater than 2 ant speeds.

ponderingturtle · 20th October 2009, 02:06 PM

Originally Posted by aggle-rithm

If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light.

The thing is that space isn't expanding at a speed, but at a percentage like say 1% per year. If it was expanding at that speed then the distance between objects more than 100 light years appart woul be increaseing at greater than the speed of light, but the distance between objects 50 LY appart would not be.

ponderingturtle · 20th October 2009, 02:08 PM

Originally Posted by JoeTheJuggler

Says who?

While we can't travel or send information faster than the speed of light, we can observe velocities faster than the speed of light.

If we used the Earth as a fixed frame of reference, then the rest of the universe is indeed moving faster than the speed of light.

This gets into definitions of what moving means.

Quote:

Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light.

No from our prospective each is moving at near C, but the distance between them is shrinking at greater than C.

ponderingturtle · 20th October 2009, 02:09 PM

Originally Posted by JoeTheJuggler

Maybe a simpler way of thinking of this.

You're at a fixed position and you shine a beam of light directly in front of you and another one exactly 180° away from it (directly behind you). The photons traveling away from you in front have a velocity of +1c and the photons traveling away from you behind have a velocity of -1c. From your perspective, they have a relative velocity of 2c to each other.

However, if you were riding on one of the photons, when you calculate your velocity relative to the photons going the opposite direction, you'd come up with a relative speed of 1c.

Not really you would come up with an error. Div0.

sol invictus · 20th October 2009, 04:17 PM

Originally Posted by JoeTheJuggler

I don't think that's what limits how much of the universe we can see.

I actually didn't say it was - I said it limits how far back in time we can see. But as Zig says, it also limits how far away in space we can see (13.7 billion light years, at least according to the natural distance measure for this discussion), because unscattered light travels in both time and space.

Quote:

That is, we know the universe is larger than what we can see of it.

Well we don't exactly know that, but anything else would be very bizarre.

Quote:

We can only see out (or back in time) as long as there has been time for that light to reach us. So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.)

I don't follow you. The oldest light we can see is the CMB, and the CMB photons last scattered 300,000 years after the big bang. We can't see past that for the same reason we can't see through brick walls. If the universe had been transparent after 200,000 years instead, we'd see CMB photons that came from 100,000 light years farther away and 100,000 years farther back in time. So the opacity is indeed what limits both how far away and how far back in time we can see.

By the way, there are other signatures we might be able to see that could look back/out even further. Neutrinos last scatter earlier than photons, for example.

RecoveringYuppy · 20th October 2009, 07:21 PM

Originally Posted by sol invictus

By the way, there are other signatures we might be able to see that could look back/out even further. Neutrinos last scatter earlier than photons, for example.

And gravity waves older than that?

sol invictus · 20th October 2009, 08:36 PM

Originally Posted by RecoveringYuppy

And gravity waves older than that?

Yes, some of them are, and they're detectable in principle. But the kind of precision experiment required to detect them is out of reach for a decade at least.

Most likely it will require something like this (which will be an absolutely incredible experiment if it works) or even more sophisticated.

Ziggurat · 20th October 2009, 11:07 PM

Originally Posted by sol invictus

Yes, some of them are, and they're detectable in principle. But the kind of precision experiment required to detect them is out of reach for a decade at least.

It's worth noting in this regard that gravity waves from the early universe will have been red-shifted just like photons, and the red-shifting will also decrease their amplitude. Both the lowering of the frequency and the decrease in amplitude will make detection harder.

edd · 21st October 2009, 05:02 AM

Originally Posted by Ziggurat

It's worth noting in this regard that gravity waves from the early universe will have been red-shifted just like photons, and the red-shifting will also decrease their amplitude. Both the lowering of the frequency and the decrease in amplitude will make detection harder.

Unlike photons, we detect gravitational waves by their amplitude rather than their intensity though.

RecoveringYuppy · 21st October 2009, 01:50 PM

Originally Posted by Ziggurat

It's worth noting in this regard that gravity waves from the early universe will have been red-shifted just like photons, and the red-shifting will also decrease their amplitude. Both the lowering of the frequency and the decrease in amplitude will make detection harder.

Presumably the universe became transparent to gravity waves very early, probably something akin to 300,000 years prior to EM transparency. Not sure my thinking is clear on this but those 300K extra years of shifting would actually cause a great deal more red shifting than the subsequent ~14 billion wouldn't they?

ETA: Was there a time when most of the universe's energy was contained in gravity waves?

Ziggurat · 21st October 2009, 02:13 PM

Originally Posted by RecoveringYuppy

Presumably the universe became transparent to gravity waves very early, probably something akin to 300,000 years prior to EM transparency. Not sure my thinking is clear on this but those 300K extra years of shifting would actually cause a great deal more red shifting than the subsequent ~14 billion wouldn't they?

I would expect so, but I'm also not sure if anyone has a good handle on what the spectrum should have looked like, or when the universe would go transparent to gravity waves, so we might not even know what to expect. But I don't keep up on these issues, so maybe more is known than I'm aware of.

19th October 2009, 07:54 AM	#1
boyntonstu Suspended Join Date: Jun 2009 Location: Florida Posts: 352	How did we get so far away so fast? How did we get so far away so fast? If we can see light from stars that originated billions of years ago, and everything started from a single point, how did we get so far away so quickly? IOW If we are 10 billion light years from an object, did we separate faster than the speed of light?

19th October 2009, 07:57 AM	#2
Seren_ Scholar Join Date: Jul 2008 Posts: 101	From what I understood, the Universe is expanding, and while some galaxies are drifting apart (and some other are getting closer), the biggest contribution to the huge distance is that the empty space inbetween has "grown". This is the usual image of ants walking on an inflattable balloon. While they are moving slowly, since the balloon is getting bigger there are further and further apart.
Seren_ Scholar Join Date: Jul 2008 Posts: 101

19th October 2009, 08:07 AM	#3
dlorde Muse Join Date: Apr 2007 Posts: 613	Originally Posted by boyntonstu If we can see light from stars that originated billions of years ago, and everything started from a single point, how did we get so far away so quickly? IOW If we are 10 billion light years from an object, did we separate faster than the speed of light? The universe is currently estimated to be almost 14 billion years old. The idea is that stuff has been expanding from that point for 14 billion years, and, as space itself expands, the most distant parts may be moving away at > c.
dlorde Muse Join Date: Apr 2007 Posts: 613

19th October 2009, 08:18 AM	#5
RecoveringYuppy Master Poster Join Date: Nov 2006 Location: Tucson, AZ Posts: 2,470	Originally Posted by boyntonstu IOW If we are 10 billion light years from an object, did we separate faster than the speed of light? There's been more than 10 billion years since the big bang, so we wouldn't need to separate faster than light to do that. But, as has already been said, there are presumably galaxies beyond the distance we can see. And some day the expansion of the universe is going to have taken the galaxies that we can see "over the edge" to where we can't see them any longer.
	__________________ REJ (Robert E Jones) posting anonymously under my real name for 30 years. Make a fire for a man and you keep him warm for a day. Set him on fire and you keep him warm for the rest of his life.

19th October 2009, 08:24 AM	#6
steenkh Master Poster Join Date: Aug 2002 Location: Denmark Posts: 2,744	Originally Posted by boyntonstu I don't understand the claim that we are viewing light from the beginning of the Universe. No. We are not seeing light from the beginning of the universe. The oldest light we can see is the Cosmic Microwave Background, which was radiated when the universe cooled sufficiently to become transparent to light, about 379,000 years after the Big Bang. Quote: If is light from the beginning that is being observed, wasn't our sun there at the same time? As you see, the atoms that make up our Sun had already moved 379,000 years by the time the CMB broke free. The light from distant galaxies is much, much younger even.
	__________________ Steen -- Jack of all trades - master of none!

19th October 2009, 08:16 AM	#4
boyntonstu Suspended Join Date: Jun 2009 Location: Florida Posts: 352	Originally Posted by dlorde The universe is currently estimated to be almost 14 billion years old. The idea is that stuff has been expanding from that point for 14 billion years, and, as space itself expands, the most distant parts may be moving away at > c. > c is supposed to be impossible. I don't understand the claim that we are viewing light from the beginning of the Universe. If is light from the beginning that is being observed, wasn't our sun there at the same time?

19th October 2009, 08:25 AM	#7
Roboramma Illuminator Join Date: Feb 2005 Location: Shanghai Posts: 3,374	Originally Posted by boyntonstu > c is supposed to be impossible. It's impossible for things to move through space faster than c. However, if the space between two objects is moving, they can be carried away from each other faster than c, in which case they will be forever lost from view. Edit: That said, remember that while there are regions that are very far away, the universe is also very old.
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov www.reddoor-yoga.com Last edited by Roboramma; 19th October 2009 at 08:27 AM.

19th October 2009, 08:31 AM	#8
H3LL Illuminator Join Date: Jul 2004 Location: A place where something is or could be located; a site. Posts: 4,458	I though light had no "age". Surely there is no such thing as "young" light or "old" light. The source of the light? Well that's OK.
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19th October 2009, 08:31 AM	#9
Dancing David Penultimate Amazing Join Date: Mar 2003 Location: Central Illinois Posts: 18,357	Originally Posted by boyntonstu How did we get so far away so fast? If we can see light from stars that originated billions of years ago, and everything started from a single point, how did we get so far away so quickly? IOW If we are 10 billion light years from an object, did we separate faster than the speed of light? Space itslef is expanding according to theory. At a certain pase there was a very fast expansion called 'inflation'. And no it did not inflate faster than the speed of light. (At least that is my understanding, because the speed of light is within space.)
	__________________ Resolve then, that on this very ground, with small flags waving and tinny blast on tiny trumpets, we shall meet the enemy, and not only may he be ours, he may be us.- Walt Kelly wow Mr.Philospher, you need some custard poured over your head mayhaps? -kittynh "Exhibit 1338A as to why the Politics forum is "where rational thought goes to die."-Carlitos

19th October 2009, 08:34 AM	#10
aggle-rithm Philosopher Join Date: Jun 2005 Location: Austin, TX Posts: 6,746	Originally Posted by Roboramma It's impossible for things to move through space faster than c. However, if the space between two objects is moving, they can be carried away from each other faster than c, in which case they will be forever lost from view. This is the basis for the warp drive theory. Although matter cannot be accellerated to the speed of light, there is nothing to prevent space from moving at the speed of light or faster. So, theoretically, if we can get a region of space that contains a spaceship in it to move faster then light, the ship will go along for the ride. The two problems are: Finding a HUGE energy source to warp the space around a ship (bigger than the lifetime output of a star, probably) and finding a way to propel that warp bubble to any speed, much less faster-than-light speeds.
	__________________ To understand recursion, you must first understand recursion. Woo's razor: Never attribute to stupidity that which can be adequately explained by aliens.

19th October 2009, 08:36 AM	#11
aggle-rithm Philosopher Join Date: Jun 2005 Location: Austin, TX Posts: 6,746	Originally Posted by Dancing David Space itslef is expanding according to theory. At a certain pase there was a very fast expansion called 'inflation'. And no it did not inflate faster than the speed of light. (At least that is my understanding, because the speed of light is within space.) If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light.
	__________________ To understand recursion, you must first understand recursion. Woo's razor: Never attribute to stupidity that which can be adequately explained by aliens.

19th October 2009, 08:36 AM	#12
steenkh Master Poster Join Date: Aug 2002 Location: Denmark Posts: 2,744	Originally Posted by H3LL I though light had no "age". Surely there is no such thing as "young" light or "old" light. Though light does not age, it still makes sense to speak about light emitted a long time ago as "older" than light emitted a short while ago.
	__________________ Steen -- Jack of all trades - master of none!

19th October 2009, 08:39 AM	#13
JHGRedekop Student Join Date: Jul 2009 Posts: 29	Originally Posted by boyntonstu > c is supposed to be impossible. It's impossible to move through space at > c, but it is not impossible for space to expand at a rate such that, between two points sufficiently far apart, the net expansion of space between them exceeds c. The difference is subtle, but important. Originally Posted by boyntonstu I don't understand the claim that we are viewing light from the beginning of the Universe. If is light from the beginning that is being observed, wasn't our sun there at the same time? No. Our sun is less than five billion years old, while the universe is over 13 billion years old.
JHGRedekop Student Join Date: Jul 2009 Posts: 29

19th October 2009, 08:39 AM	#14
steenkh Master Poster Join Date: Aug 2002 Location: Denmark Posts: 2,744	Originally Posted by aggle-rithm If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light. Should that not read "red-shifted"?
	__________________ Steen -- Jack of all trades - master of none!

19th October 2009, 08:58 AM	#15
lomiller Master Poster Join Date: Jul 2007 Posts: 2,346	While I’m not exactly an expert on this, my understanding is that it isn’t correct to say the universe is expanding from a single point. A closer analogy is that the point the universe occupied at the big bang is itself expanding. That’s only my way of understanding it so it’s probably a deficient explanation in any number of ways.
lomiller Master Poster Join Date: Jul 2007 Posts: 2,346	__________________ War, war never changes...

19th October 2009, 09:03 AM	#16
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 10,998	Originally Posted by boyntonstu How did we get so far away so fast? So far away from what? You could as well consider stuff that is at the limits of our ability to see (c. 14 billion light years) and beyond to have gotten far away from us rather than us to have gotten far away from it. There is no center or edge--just expansion. And it's been going on for nearly 14 billion years. So. . how fast is "so fast"?
	__________________ "That is a very graphic analogy which aids understanding wonderfully while being, strictly speaking, wrong in every possible way." —Ponder Stibbons

19th October 2009, 09:12 AM	#17
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 10,998	Originally Posted by boyntonstu > c is supposed to be impossible. Says who? While we can't travel or send information faster than the speed of light, we can observe velocities faster than the speed of light. If we used the Earth as a fixed frame of reference, then the rest of the universe is indeed moving faster than the speed of light. Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light. Relativity does not claim that speeds faster than light are impossible in all cases. Depending on what you mean, it is certainly possible for the universe to expand faster than the speed of light.
	__________________ "That is a very graphic analogy which aids understanding wonderfully while being, strictly speaking, wrong in every possible way." —Ponder Stibbons

19th October 2009, 09:21 AM	#18
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 10,998	Originally Posted by JoeTheJuggler Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light. Maybe a simpler way of thinking of this. You're at a fixed position and you shine a beam of light directly in front of you and another one exactly 180° away from it (directly behind you). The photons traveling away from you in front have a velocity of +1c and the photons traveling away from you behind have a velocity of -1c. From your perspective, they have a relative velocity of 2c to each other. However, if you were riding on one of the photons, when you calculate your velocity relative to the photons going the opposite direction, you'd come up with a relative speed of 1c.
	__________________ "That is a very graphic analogy which aids understanding wonderfully while being, strictly speaking, wrong in every possible way." —Ponder Stibbons

19th October 2009, 09:30 AM	#19
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 10,998	Originally Posted by boyntonstu I don't understand the claim that we are viewing light from the beginning of the Universe. If is light from the beginning that is being observed, wasn't our sun there at the same time? No. The Big Bang was nearly 14 billion years ago. The Sun is only about 4.6 billion years old.
	__________________ "That is a very graphic analogy which aids understanding wonderfully while being, strictly speaking, wrong in every possible way." —Ponder Stibbons

19th October 2009, 11:05 AM	#20
soylent Muse Join Date: Dec 2007 Location: Stockholm, Sweden Posts: 657	Originally Posted by steenkh Should that not read "red-shifted"? Yes, hence cosmic microwave background rather than cosmic x-ray background.
	__________________ "A lot of those lobbyists genuinely like people. But then, fleas like people too." - Mike Munger.

19th October 2009, 11:23 AM	#21
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 13,874	Originally Posted by boyntonstu I don't understand the claim that we are viewing light from the beginning of the Universe. We aren't. The very early universe was opaque, so any light emitted during that very early period was absorbed, and no longer exists. It wasn't until around 300,000 years after the big bang that the universe became mostly transparent, and that is when the thermal background radiation of the universe originated. That background (which has cooled down with the expansion of the universe) is now known as the cosmic microwave background (CMB), and it is the oldest light we can see, and the oldest light we ever will be able to see. But it is NOT as old as the universe itself. Stars and galaxies didn't form until sometime after the universe became transparent, so there's actually a gap in time between the CMB and the oldest stars and galaxies.
	__________________ "There is certainly not one government in Europe but is now watching the war in this country, with the ardent prayer that the united States may be effectually split, crippled, and dismember'd by it... We are all too prone to wander from ourselves, to affect Europe, and watch her frowns and smiles. We need this hot lesson of general hatred, and henceforth must never forget it. Never again will we trust the moral sense nor abstract friendliness of a single government of the world." - Walt Whitman, 1864

19th October 2009, 11:40 AM	#22
Eyeron Guest Join Date: Jul 2009 Posts: 1,774	Okay, I'm confused, I've never heard that the universe is transparent. What exactly does that mean?
Eyeron Guest Join Date: Jul 2009 Posts: 1,774

19th October 2009, 11:53 AM	#23
Paul C. Anagnostopoulos Looking for Fountain of Smart Join Date: Aug 2001 Location: a little toolshed Posts: 17,157	Originally Posted by Eyeron Okay, I'm confused, I've never heard that the universe is transparent. What exactly does that mean? It means that you can see through it. Prior to 300,000 BB, you couldn't see through the dense stuff making up the universe because photons couldn't travel more or less freely. Not that you were around then, of course. http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang ~~ Paul
	__________________ Millions long for immortality who do not know what to do with themselves on a rainy Sunday afternoon. ---Susan Ertz pi = 3.1415926...19729715941700531415926095214704122509... Last edited by Paul C. Anagnostopoulos; 19th October 2009 at 11:54 AM.

19th October 2009, 12:09 PM	#24
MervinFerd Thinker Join Date: Dec 2008 Posts: 176	Originally Posted by Paul C. Anagnostopoulos It means that you can see through it. Prior to 300,000 BB, you couldn't see through the dense stuff making up the universe because photons couldn't travel more or less freely. Not that you were around then, of course. ~~ Paul That's probably a GOOD thing.
MervinFerd Thinker Join Date: Dec 2008 Posts: 176

20th October 2009, 06:52 AM	#25
aggle-rithm Philosopher Join Date: Jun 2005 Location: Austin, TX Posts: 6,746	Originally Posted by steenkh Should that not read "red-shifted"? That's what I was wondering as I typed it.
	__________________ To understand recursion, you must first understand recursion. Woo's razor: Never attribute to stupidity that which can be adequately explained by aliens.

20th October 2009, 01:20 PM	#26
Corsair 115 Illuminator Join Date: Apr 2007 Location: Tranquility Base Posts: 4,338	Folks may want to check out the following program which aired on TVO a couple of weeks back. It was a lecture given by Lawrence Krauss, a professor in the Department of Physics at Arizona State University. The lecture, entitled Life, the Universe and Nothing, touched upon some of the subjects mentioned in this thread. I personally found it quite interesting. I can't say if the link and its video will work for non-Canadians, but I'll post it anyway: Lawrence Krauss on dark energy and the end of the universe
	__________________ "We choose to go to the moon in this decade and do the other things not because they are easy, but because they are hard. Because that goal will serve to organize and measure the best of our abilities and skills, because that challenge is one we are willing to accept, one we are unwilling to postpone, and one which we intend to win."

20th October 2009, 01:28 PM	#27
sol invictus Philosopher Join Date: Oct 2007 Location: Nova Roma Posts: 5,153	Originally Posted by boyntonstu > c is supposed to be impossible. I don't understand the claim that we are viewing light from the beginning of the Universe. If is light from the beginning that is being observed, wasn't our sun there at the same time? You know how at a fireworks display, you hear the explosions a second or so after they happen? The sounds you hear at any given moment are always a combination of sounds emitted nearby right then, sounds emitted 1 second earlier from something 343 meters away, sounds emitted 2 seconds earlier 686 meters away, everything in between, etc. So you're always hearing a continuum of "old" and "new" sound (you don't normally notice this, since sounds from far away are rarely loud enough to hear). The same goes for light. The sun is nearby, so the light you're seeing from it now is only about 8 minutes old (it was emitted 8 minutes ago). The light we see from Alpha Centauri, the nearest star to the sun, was emitted about 4.4 years ago. The further you look, the older the light is, and so if there was nothing in the way you could see all the way back to the beginning in the universe by looking at light coming from really distant sources. But as Zig pointed out, there is something in the way - the universe was opaque to light up to about 300,000 years, so that's as far back as we can see directly. The "light" from that time is called cosmic microwave background radiation.

20th October 2009, 01:42 PM	#28
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 10,998	Originally Posted by sol invictus But as Zig pointed out, there is something in the way - the universe was opaque to light up to about 300,000 years, so that's as far back as we can see directly. I don't think that's what limits how much of the universe we can see. That is, we know the universe is larger than what we can see of it. We can only see out (or back in time) as long as there has been time for that light to reach us. So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.)
	__________________ "That is a very graphic analogy which aids understanding wonderfully while being, strictly speaking, wrong in every possible way." —Ponder Stibbons

20th October 2009, 01:59 PM	#29
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 13,874	Originally Posted by JoeTheJuggler I don't think that's what limits how much of the universe we can see. That is, we know the universe is larger than what we can see of it. We can only see out (or back in time) as long as there has been time for that light to reach us. Yes, but the relevant time limit is set by when the universe became transparent, not by when the universe began, so that does indeed limit how much of the universe we can see. Quote: So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.) I don't see what point you're trying to make. We see that opaque barrier (that's what the CMB is), so we definitely are running up against that limit. And since the universe went from opaque to transparent everywhere, the distinction between size, distance, and age issue isn't relevant. Perhaps you are confusing this limit with the oldest stars we can see (which are not as far away or as old as this opaque boundary), but that's a different issue.
	__________________ "There is certainly not one government in Europe but is now watching the war in this country, with the ardent prayer that the united States may be effectually split, crippled, and dismember'd by it... We are all too prone to wander from ourselves, to affect Europe, and watch her frowns and smiles. We need this hot lesson of general hatred, and henceforth must never forget it. Never again will we trust the moral sense nor abstract friendliness of a single government of the world." - Walt Whitman, 1864

20th October 2009, 02:02 PM	#30
ponderingturtle Orthogonal Vector Join Date: Jul 2006 Location: Ossining NY Posts: 18,770	Originally Posted by boyntonstu > c is supposed to be impossible. Speeds greater than C are imposible, what this is a rate in increase of the distance between to points increaseing with time. That might seem like the same thing but it is only if you view space itself as fixed and not expanding. See the ants on the balloon analogy. They are walking away from each other at a certain speed, but that speed can be increased if you inflate the baloon at the same time. Relative to the baloon each of them is moving at the ant speed but the distance between them is increaseing at greater than 2 ant speeds.
	__________________ Sufficiently advanced Woo is indistinguishable from Parody "There shall be no poofing in science" Paul C. Anagnostopoulos Force ***** on reasons back" Ben Franklin

20th October 2009, 02:06 PM	#31
ponderingturtle Orthogonal Vector Join Date: Jul 2006 Location: Ossining NY Posts: 18,770	Originally Posted by aggle-rithm If space expands faster than light, then the light within it would be blue-shifted a great deal but would still move at the speed of light. The thing is that space isn't expanding at a speed, but at a percentage like say 1% per year. If it was expanding at that speed then the distance between objects more than 100 light years appart woul be increaseing at greater than the speed of light, but the distance between objects 50 LY appart would not be.
	__________________ Sufficiently advanced Woo is indistinguishable from Parody "There shall be no poofing in science" Paul C. Anagnostopoulos Force ***** on reasons back" Ben Franklin

20th October 2009, 02:08 PM	#32
ponderingturtle Orthogonal Vector Join Date: Jul 2006 Location: Ossining NY Posts: 18,770	Originally Posted by JoeTheJuggler Says who? While we can't travel or send information faster than the speed of light, we can observe velocities faster than the speed of light. If we used the Earth as a fixed frame of reference, then the rest of the universe is indeed moving faster than the speed of light. This gets into definitions of what moving means. Quote: Also consider yourself at a point witnessing two ships traveling in opposite directions at very close to the speed of light. From our perspective, their relative speed would be faster than the speed of light, but from each of their points of view, they would not have a relative speed faster than light. No from our prospective each is moving at near C, but the distance between them is shrinking at greater than C.
	__________________ Sufficiently advanced Woo is indistinguishable from Parody "There shall be no poofing in science" Paul C. Anagnostopoulos Force ***** on reasons back" Ben Franklin

20th October 2009, 02:09 PM	#33
ponderingturtle Orthogonal Vector Join Date: Jul 2006 Location: Ossining NY Posts: 18,770	Originally Posted by JoeTheJuggler Maybe a simpler way of thinking of this. You're at a fixed position and you shine a beam of light directly in front of you and another one exactly 180° away from it (directly behind you). The photons traveling away from you in front have a velocity of +1c and the photons traveling away from you behind have a velocity of -1c. From your perspective, they have a relative velocity of 2c to each other. However, if you were riding on one of the photons, when you calculate your velocity relative to the photons going the opposite direction, you'd come up with a relative speed of 1c. Not really you would come up with an error. Div0.
	__________________ Sufficiently advanced Woo is indistinguishable from Parody "There shall be no poofing in science" Paul C. Anagnostopoulos Force ***** on reasons back" Ben Franklin

20th October 2009, 04:17 PM	#34
sol invictus Philosopher Join Date: Oct 2007 Location: Nova Roma Posts: 5,153	Originally Posted by JoeTheJuggler I don't think that's what limits how much of the universe we can see. I actually didn't say it was - I said it limits how far back in time we can see. But as Zig says, it also limits how far away in space we can see (13.7 billion light years, at least according to the natural distance measure for this discussion), because unscattered light travels in both time and space. Quote: That is, we know the universe is larger than what we can see of it. Well we don't exactly know that, but anything else would be very bizarre. Quote: We can only see out (or back in time) as long as there has been time for that light to reach us. So we can only see nearly 14 billion light years, but we know the universe is larger than that (that is, the average speed of expansion exceeds the speed of light--so seeing back nearly 14 billion years doesn't yet run us up against the limit of the opaque universe of the first 300,000 years following the Big Bang.) I don't follow you. The oldest light we can see is the CMB, and the CMB photons last scattered 300,000 years after the big bang. We can't see past that for the same reason we can't see through brick walls. If the universe had been transparent after 200,000 years instead, we'd see CMB photons that came from 100,000 light years farther away and 100,000 years farther back in time. So the opacity is indeed what limits both how far away and how far back in time we can see. By the way, there are other signatures we might be able to see that could look back/out even further. Neutrinos last scatter earlier than photons, for example.

20th October 2009, 07:21 PM	#35
RecoveringYuppy Master Poster Join Date: Nov 2006 Location: Tucson, AZ Posts: 2,470	Originally Posted by sol invictus By the way, there are other signatures we might be able to see that could look back/out even further. Neutrinos last scatter earlier than photons, for example. And gravity waves older than that?
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