Moving through space

Skeptic believer · 20th December 2011, 12:38 AM

A simple science question that occured to me

Would it be possible to travel through empty space by continually changing your shape?

E.g. Would an amoeba have the ability to freely move within a weightless environment?

epepke · 20th December 2011, 12:43 AM

Originally Posted by Skeptic believer

A simple science question that occured to me

Would it be possible to travel through empty space by continually changing your shape?

E.g. Would an amoeba have the ability to freely move within a weightless environment?

No. Not due to weightlessness, which isn't relevant, but due to not having anything to push or squirm or slither against.

You can see this because of the conservation of momentum. Actually, it's even easier than that. This has to be true for everything, but let's take a rocket. You have the rocket and all its fuel and everything. It has a center of mass. Then the rockets go on, and it moves. If you take everything into account, the rocket and the stuff that comes out the back, the center of mass hasn't changed.

ETA: A snake can move by slithering in grass, but it can only go forward if the grass goes backward. The grass bone is connected to the Earth bone. So, for even a snake to move in one direction, the Earth has to move in the opposite direction. Not much, because snakes aren't very big, but some.

Vorpal · 20th December 2011, 12:48 AM

I suppose if the organism has a lot of time on its hands, changing shape in order to make thermal radiation pressure uneven would work in a vacuum in a very, very limited way. But yes, momentum conservation is a harsh mistress.

Skeptic believer · 20th December 2011, 01:31 AM

Originally Posted by epepke

ETA: A snake can move by slithering in grass, but it can only go forward if the grass goes backward. The grass bone is connected to the Earth bone. So, for even a snake to move in one direction, the Earth has to move in the opposite direction. Not much, because snakes aren't very big, but some.

But an amoeba doesn't need anything to push against to change its shape, which is why I used it as an example

Originally Posted by epepke

You can see this because of the conservation of momentum.

Assume that. for the purposes of the experiment. you define yourself as stationary within space - Thus no momentum (in your frame of reference).

If you are sitting on a long seat in space, which has the ability to elongate or contract, either left or right -

Without moving through space, you elongate the right side, and then move to your right - Then you contract the left side.
Thus, you will in effect have moved slightly towards the right, but your momentum hasn't changed, as you remain stationary (in the unaltered frame of reference).

You are simply changing your position by using the changing shape of the seat as a sort of step ladder - but your momentum doesn't change, so that doesn't come into it

In this way, you will be able to slowly cross space

or will you (??)

epepke · 20th December 2011, 01:47 AM

Originally Posted by Skeptic believer

But an amoeba doesn't need anything to push against to change its shape, which is why I used it as an example

An amoeba lives in water, which it can push against.

Quote:

Without moving through space, you elongate the right side, and then move to you right - Then you comtact the left side.

No. The center of mass does not move. When you elongate the right side, it pushes the rest to the left, and the center of mass does not move.

Lamuella · 20th December 2011, 01:48 AM

Originally Posted by Skeptic believer

Assume that. for the purposes of the experiment. you define yourself as stationary within space - Thus no momentum (in your frame of reference).

If you are sitting on a long seat in space, which has the ability to elongate or contract, either left or right -

Without moving through space, you elongate the right side, and then move to you right - Then you comtact the left side.

Newton's third law of motion. Trying to "move to your right" will move the seat to your left. Your ultimate position will be the same.

Ziggurat · 20th December 2011, 01:57 AM

Actually, it IS possible to "swim" in a gravitational field without pushing against anything, just by changing shape. Essentially what you're doing is radiating gravitational waves. But it's horrifically inefficient, and the effects would be far too small at non-relativistic speeds to make any noticeable difference.

nvidiot · 20th December 2011, 01:59 AM

There was an American scientist article on this a while back. It is possible to do, but as Ziggurat points out, it's nearly pointless.

Vorpal · 20th December 2011, 02:00 AM

Oho! 'Swimming' in electromagnetic radiation is bad enough already. But theoretically a good idea; didn't think of that.

Skeptic believer · 20th December 2011, 02:13 AM

Thankyou

That seems to sort that out

Pulvinar · 20th December 2011, 05:05 AM

Originally Posted by Skeptic believer

A simple science question that occured to me

Would it be possible to travel through empty space by continually changing your shape?

E.g. Would an amoeba have the ability to freely move within a weightless environment?

Yes, by jet power, if ejecting a part could be considered changing shape.

Molinaro · 20th December 2011, 07:03 AM

Originally Posted by Pulvinar

Yes, by jet power, if ejecting a part could be considered changing shape.

Topologically speaking, no it cannot be considered changing shape.

And I remember reading that article mentioned earlier.

AvalonXQ · 20th December 2011, 07:08 AM

In line with what others have pointed out -- if you can split yourself, you can move part of yourself anywhere by having the other part go the other way. This is exactly how a rocket moves.
Similarly, if you can stretch yourself out, you can get as far as you can stretch. But again, your center of mass stays in the same place, so any stretching should ideally involve stretching in both directions.

Molinaro · 20th December 2011, 07:51 AM

Here's a brief summary of the article as it appeared in Scientific American: http://www.scientificamerican.com/ar...ral-relativity

quarky · 20th December 2011, 08:18 AM

Farting could work.

I wondered something similar in trying to figure out how 'scootching' works.
You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does.

I Ratant · 20th December 2011, 08:51 AM

Originally Posted by Vorpal

I suppose if the organism has a lot of time on its hands, changing shape in order to make thermal radiation pressure uneven would work in a vacuum in a very, very limited way. But yes, momentum conservation is a harsh mistress.

.
A solar sail.

I Ratant · 20th December 2011, 08:53 AM

Originally Posted by quarky

Farting could work.

I wondered something similar in trying to figure out how 'scootching' works.
You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does.

.
Farting loses mass.
Expanding to a sail lets the solar wind push you.

Modified · 20th December 2011, 01:37 PM

Originally Posted by quarky

I wondered something similar in trying to figure out how 'scootching' works.
You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does.

Resistance doesn't scale evenly with speed.

kalen · 20th December 2011, 02:26 PM

Originally Posted by Ziggurat

Actually, it IS possible to "swim" in a gravitational field without pushing against anything, just by changing shape. Essentially what you're doing is radiating gravitational waves. But it's horrifically inefficient, and the effects would be far too small at non-relativistic speeds to make any noticeable difference.

Since you are radiating gravitational waves, are you not also radiating energy and losing mass in the process? I would say a loss of mass does not equate to a strict "change of shape."

By the same token, a body could also radiate EM waves by changing its internal charge distribution in an appropriate way, and move without "pushing against anything." Again, energy is being radiated away and a loss of mass would result. This would be much more efficient than radiating gravitational waves as the EM force is much stronger.

Ziggurat · 20th December 2011, 02:28 PM

Originally Posted by kalen

Since you are radiating gravitational waves, are you not also radiating energy and losing mass in the process?

Absolutely.

I Ratant · 20th December 2011, 03:39 PM

Originally Posted by I Ratant

.
Farting loses mass.
Expanding to a sail lets the solar wind push you.

.
And when you get fast enough, morph into a Bussard Ramjet and really accelerate!

quarky · 20th December 2011, 04:13 PM

Seems that any living organism has some excretion/exhalation/farting going on. Thrusters, potentially, however marginal.

20th December 2011, 12:38 AM	#1
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20	Moving through space A simple science question that occured to me Would it be possible to travel through empty space by continually changing your shape? E.g. Would an amoeba have the ability to freely move within a weightless environment?
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20

20th December 2011, 12:43 AM	#2
epepke Philosopher Join Date: Oct 2003 Posts: 7,950	Originally Posted by Skeptic believer A simple science question that occured to me Would it be possible to travel through empty space by continually changing your shape? E.g. Would an amoeba have the ability to freely move within a weightless environment? No. Not due to weightlessness, which isn't relevant, but due to not having anything to push or squirm or slither against. You can see this because of the conservation of momentum. Actually, it's even easier than that. This has to be true for everything, but let's take a rocket. You have the rocket and all its fuel and everything. It has a center of mass. Then the rockets go on, and it moves. If you take everything into account, the rocket and the stuff that comes out the back, the center of mass hasn't changed. ETA: A snake can move by slithering in grass, but it can only go forward if the grass goes backward. The grass bone is connected to the Earth bone. So, for even a snake to move in one direction, the Earth has to move in the opposite direction. Not much, because snakes aren't very big, but some.
epepke Philosopher Join Date: Oct 2003 Posts: 7,950	__________________ "It probably came from a sticky dark planet far, far away." - Godzilla versus Hedora "There's no evidence that the 9-11 attacks (whoever did them) were deliberately attacking civilians. On the contrary the targets appear to have been chosen as military." -DavidByron Last edited by epepke; 20th December 2011 at 12:45 AM.

20th December 2011, 12:48 AM	#3
Vorpal Extrapolate! Join Date: Jan 2005 Posts: 1,008	I suppose if the organism has a lot of time on its hands, changing shape in order to make thermal radiation pressure uneven would work in a vacuum in a very, very limited way. But yes, momentum conservation is a harsh mistress.
Vorpal Extrapolate! Join Date: Jan 2005 Posts: 1,008	__________________ For every philosopher, there exists an equal and opposite philosopher. They're both wrong.

20th December 2011, 01:31 AM	#4
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20	Originally Posted by epepke ETA: A snake can move by slithering in grass, but it can only go forward if the grass goes backward. The grass bone is connected to the Earth bone. So, for even a snake to move in one direction, the Earth has to move in the opposite direction. Not much, because snakes aren't very big, but some. But an amoeba doesn't need anything to push against to change its shape, which is why I used it as an example Originally Posted by epepke You can see this because of the conservation of momentum. Assume that. for the purposes of the experiment. you define yourself as stationary within space - Thus no momentum (in your frame of reference). If you are sitting on a long seat in space, which has the ability to elongate or contract, either left or right - Without moving through space, you elongate the right side, and then move to your right - Then you contract the left side. Thus, you will in effect have moved slightly towards the right, but your momentum hasn't changed, as you remain stationary (in the unaltered frame of reference). You are simply changing your position by using the changing shape of the seat as a sort of step ladder - but your momentum doesn't change, so that doesn't come into it In this way, you will be able to slowly cross space or will you (??)
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20	Last edited by Skeptic believer; 20th December 2011 at 02:03 AM.

20th December 2011, 01:47 AM	#5
epepke Philosopher Join Date: Oct 2003 Posts: 7,950	Originally Posted by Skeptic believer But an amoeba doesn't need anything to push against to change its shape, which is why I used it as an example An amoeba lives in water, which it can push against. Quote: Without moving through space, you elongate the right side, and then move to you right - Then you comtact the left side. No. The center of mass does not move. When you elongate the right side, it pushes the rest to the left, and the center of mass does not move.
epepke Philosopher Join Date: Oct 2003 Posts: 7,950	__________________ "It probably came from a sticky dark planet far, far away." - Godzilla versus Hedora "There's no evidence that the 9-11 attacks (whoever did them) were deliberately attacking civilians. On the contrary the targets appear to have been chosen as military." -DavidByron

20th December 2011, 01:48 AM	#6
Lamuella Master Poster Join Date: Mar 2006 Posts: 2,480	Originally Posted by Skeptic believer Assume that. for the purposes of the experiment. you define yourself as stationary within space - Thus no momentum (in your frame of reference). If you are sitting on a long seat in space, which has the ability to elongate or contract, either left or right - Without moving through space, you elongate the right side, and then move to you right - Then you comtact the left side. Newton's third law of motion. Trying to "move to your right" will move the seat to your left. Your ultimate position will be the same.
Lamuella Master Poster Join Date: Mar 2006 Posts: 2,480

20th December 2011, 01:57 AM	#7
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,197	Actually, it IS possible to "swim" in a gravitational field without pushing against anything, just by changing shape. Essentially what you're doing is radiating gravitational waves. But it's horrifically inefficient, and the effects would be far too small at non-relativistic speeds to make any noticeable difference.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

20th December 2011, 01:59 AM	#8
nvidiot Botanical Jedi Join Date: Apr 2010 Posts: 1,793	There was an American scientist article on this a while back. It is possible to do, but as Ziggurat points out, it's nearly pointless.
nvidiot Botanical Jedi Join Date: Apr 2010 Posts: 1,793	__________________ www.horsemen-gaming.com

20th December 2011, 02:00 AM	#9
Vorpal Extrapolate! Join Date: Jan 2005 Posts: 1,008	Oho! 'Swimming' in electromagnetic radiation is bad enough already. But theoretically a good idea; didn't think of that.
Vorpal Extrapolate! Join Date: Jan 2005 Posts: 1,008	__________________ For every philosopher, there exists an equal and opposite philosopher. They're both wrong.

20th December 2011, 02:13 AM	#10
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20	Thankyou That seems to sort that out
Skeptic believer New Blood Join Date: Jul 2011 Posts: 20

20th December 2011, 05:05 AM	#11
Pulvinar Muse Join Date: Aug 2009 Posts: 819	Originally Posted by Skeptic believer A simple science question that occured to me Would it be possible to travel through empty space by continually changing your shape? E.g. Would an amoeba have the ability to freely move within a weightless environment? Yes, by jet power, if ejecting a part could be considered changing shape.
Pulvinar Muse Join Date: Aug 2009 Posts: 819

20th December 2011, 07:03 AM	#12
Molinaro Illuminator Join Date: Dec 2005 Location: Toronto Posts: 3,031	Originally Posted by Pulvinar Yes, by jet power, if ejecting a part could be considered changing shape. Topologically speaking, no it cannot be considered changing shape. And I remember reading that article mentioned earlier.
	__________________ 100% Cannuck!

20th December 2011, 07:08 AM	#13
AvalonXQ Guest Join Date: Sep 2009 Posts: 11,853	In line with what others have pointed out -- if you can split yourself, you can move part of yourself anywhere by having the other part go the other way. This is exactly how a rocket moves. Similarly, if you can stretch yourself out, you can get as far as you can stretch. But again, your center of mass stays in the same place, so any stretching should ideally involve stretching in both directions.
AvalonXQ Guest Join Date: Sep 2009 Posts: 11,853

20th December 2011, 07:51 AM	#14
Molinaro Illuminator Join Date: Dec 2005 Location: Toronto Posts: 3,031	Here's a brief summary of the article as it appeared in Scientific American: http://www.scientificamerican.com/ar...ral-relativity
	__________________ 100% Cannuck!

20th December 2011, 08:18 AM	#15
quarky Banned Join Date: Oct 2007 Posts: 20,454	Farting could work. I wondered something similar in trying to figure out how 'scootching' works. You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does.
quarky Banned Join Date: Oct 2007 Posts: 20,454

20th December 2011, 08:51 AM	#16
I Ratant Penultimate Amazing Join Date: Apr 2008 Posts: 15,305	Originally Posted by Vorpal I suppose if the organism has a lot of time on its hands, changing shape in order to make thermal radiation pressure uneven would work in a vacuum in a very, very limited way. But yes, momentum conservation is a harsh mistress. . A solar sail.

20th December 2011, 08:53 AM	#17
I Ratant Penultimate Amazing Join Date: Apr 2008 Posts: 15,305	Originally Posted by quarky Farting could work. I wondered something similar in trying to figure out how 'scootching' works. You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does. . Farting loses mass. Expanding to a sail lets the solar wind push you.

20th December 2011, 01:37 PM	#18
Modified Illuminator Join Date: Sep 2006 Location: SW Florida Posts: 4,062	Originally Posted by quarky I wondered something similar in trying to figure out how 'scootching' works. You can propel a canoe in still water without a paddle, by lurching forward, and slowly coming back. It doesn't seem like it should work, but it does. Resistance doesn't scale evenly with speed.

20th December 2011, 02:26 PM	#19
kalen Your Daddy Join Date: Mar 2004 Location: Classified Posts: 933	Originally Posted by Ziggurat Actually, it IS possible to "swim" in a gravitational field without pushing against anything, just by changing shape. Essentially what you're doing is radiating gravitational waves. But it's horrifically inefficient, and the effects would be far too small at non-relativistic speeds to make any noticeable difference. Since you are radiating gravitational waves, are you not also radiating energy and losing mass in the process? I would say a loss of mass does not equate to a strict "change of shape." By the same token, a body could also radiate EM waves by changing its internal charge distribution in an appropriate way, and move without "pushing against anything." Again, energy is being radiated away and a loss of mass would result. This would be much more efficient than radiating gravitational waves as the EM force is much stronger.
	__________________ No way! Yahweh!

20th December 2011, 02:28 PM	#20
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,197	Originally Posted by kalen Since you are radiating gravitational waves, are you not also radiating energy and losing mass in the process? Absolutely.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

20th December 2011, 03:39 PM	#21
I Ratant Penultimate Amazing Join Date: Apr 2008 Posts: 15,305	Originally Posted by I Ratant . Farting loses mass. Expanding to a sail lets the solar wind push you. . And when you get fast enough, morph into a Bussard Ramjet and really accelerate!

20th December 2011, 04:13 PM	#22
quarky Banned Join Date: Oct 2007 Posts: 20,454	Seems that any living organism has some excretion/exhalation/farting going on. Thrusters, potentially, however marginal.
quarky Banned Join Date: Oct 2007 Posts: 20,454