Can a spaceman survive length contraction?

[asprung]

According to SR a body moving through space contracts in the direction of the velocity. Approaching the speed this can be substantial. It is questioned what damage this might do to a spaceman? His brain and other organs are not designed to function in a distorted condition nor at an increased density.

[Klaynos]

In the spaceman's rest frame (from his perspective) he is still the same size and you have shrunk.

[Sisyphus]

He doesn’t experience length contraction or increased density himself. This is a matter of keeping in mind your reference frame, and remembering that there is no such thing as absolute velocity, only relative velocity. He isn’t moving relative to himself, obviously, so in his own reference frame his own velocity is zero. If he’s moving that fast relative to, say, the Earth, then he will be contracted and have increased density in the reference frame in which the Earth is motionless. In his own reference frame, though, it is the Earth which has increased density, and which is flattened.

[Mokele]

So does the fact that some bodily functions (let's say circulation, to keep it clean) are moving parallel to his direction of motion and others moving perpendicular matter?

[NowThatWeKnow]

So does the fact that some bodily functions (let's say circulation, to keep it clean) are moving parallel to his direction of motion and others moving perpendicular matter?

 

No, not any more then it would matter to you right here, right now. You are both at rest in your own frame.

[Sisyphus]

We're also already moving at 0.9999999C in various frames.

[swansont]

So does the fact that some bodily functions (let's say circulation, to keep it clean) are moving parallel to his direction of motion and others moving perpendicular matter?

 

You have to remember that the description of how the body works will have to vary from frame to frame. Most of the values you might measure are not invariant, so they will be different in each frame. So if you were able to measure pulse and blood pressure from your frame somehow, it would not be the 80 and 120/80 that is measured in the astronaut's frame. You might conclude that the astronaut's sphygmomanometer was off, much like his clock was off in measuring the pulse.

 

But once you get past time and distance, it gets even more convoluted in trying to figure out the transformations.

[asprung]

Are you saying that he realy doesnt shrink in length,it just appears so to others? It seems to me a body has a certain raito of length to width and it either changers or doesnt.

[iNow]

And that's a big part of the reason why you continue to be so confused.

[Sisyphus]

Are you saying that he realy doesnt shrink in length,it just appears so to others? It seems to me a body has a certain raito of length to width and it either changers or doesnt.

 

Yes and no. Your length and mass are frame-dependent. In a frame in which you are moving, you are compressed and densified. There is no reason to choose one frame as “real” and every other frame as “just appearances,” so you are both. However, what you personally actually experience is always going to be your own rest frame, in which you have zero velocity and thus zero compression, etc. Again, though, that’s not to say that frame of reference is somehow more real than one in which you’re moving at 0.9999C, and have all sorts of wacky stuff going on.

[asprung]

The spaceman has only one body and it either shrinks or does not. If it shrinks he may have problems.

[NowThatWeKnow]

The spaceman has only one body and it either shrinks or does not. If it shrinks he may have problems.

If you look in a distorted mirror you will look distorted but it doesn't mean you are distorted. It does not shrink.

 

This brings up another question. I know there is red shift because of the expansion of space, but is there time dilation and length contraction because of the expansion of space? Or is time dilation and length contraction only caused by movement relative to the CMB.

 

If the expansion of space does cause time dilation, what is time doing in galaxies so far away they are separating at MORE then the speed of light?

[Mr Skeptic]

Not only will he survive, he won't even notice any difference. In fact, you are already moving at .99999999 c in a different reference frame, and you don't notice any length contraction do you?

[Sisyphus]

The spaceman has only one body and it either shrinks or does not. If it shrinks he may have problems.

 

If you look in a distorted mirror you will look distorted but it doesn't mean you are distorted. It does not shrink.

 

But with relativistic velocities, it does shrink, in the applicable reference frames. It's not just an illusion, as with a mirror. A twenty foot pole moving fast enough will fit inside a ten foot room, in the reference frame where the room isn't moving. Of course, in the reference frame with where the pole isn't moving, the pole is still 20 feet long, and it's the room which has shrunk. Believe it or not, this actually doesn't cause a paradox:

 

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

 

This brings up another question. I know there is red shift because of the expansion of space, but is there time dilation and length contraction because of the expansion of space? Or is time dilation and length contraction only caused by movement relative to the CMB.

 

If the expansion of space does cause time dilation, what is time doing in galaxies so far away they are separating at MORE then the speed of light?

 

Interesting. I don't know, but I'm thinking it can't work the same way as motion, if only because at some point they'd all have infinite momentum, and then beyond...

 

Oh, and it's not caused by motion relative to the CMB. "At rest with respect to the CMB" is convenient but not priveleged. It's caused by motion relative to whatever reference frame it's considered in.

[asprung]

If the spaceman is traveling at .9C I am told there should be substantial length contraction which is physical and not illusory. This could kill him. He may feel at rest inside his space ship. How would this change things? Could he be dead with respect to certain reference frames and alive and well with respect to others?

Edited May 8, 2009 by asprung

[iNow]

... deleted ...

Edited May 8, 2009 by iNow
sigh

[Sisyphus]

If the spaceman is traveling at .9C I am told there should be substantial length contraction which is physical and not illusory. This could kill him. He may feel at rest inside his space ship. How would this change things? Could he be dead with respect to certain refrence frames and alive and well with respect to others?

 

You can't be traveling at .9C. You can only be traveling at .9C relative to something else, and that something else will be traveling at .9C relative to you.

 

Anyway, it won't kill you, because you're not experiencing it. It's someone in that other reference frame who is experiencing your odd condition, and you who is experiencing theirs. But that doesn't make it illusory - you really can fit that other person inside a smaller container, etc. They really are that small, in the appropriate reference frame. Much like their time is moving slower in your reference frame, but they don't experience anything unusual, except when they look at you and see your time moving slower.

[J.C.MacSwell]

But with relativistic velocities, it does shrink, in the applicable reference frames. It's not just an illusion, as with a mirror. A twenty foot pole moving fast enough will fit inside a ten foot room, in the reference frame where the room isn't moving. Of course, in the reference frame with where the pole isn't moving, the pole is still 20 feet long, and it's the room which has shrunk. Believe it or not, this actually doesn't cause a paradox:

 

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

 

 

 

Interesting. I don't know, but I'm thinking it can't work the same way as motion, if only because at some point they'd all have infinite momentum, and then beyond...

 

Oh, and it's not caused by motion relative to the CMB. "At rest with respect to the CMB" is convenient but not priveleged. It's caused by motion relative to whatever reference frame it's considered in.

 

The CMB frame is only an inertial frame locally, or more of a continuum of frames. There's lot's of fun to be had with this. If you go strictly by SR anything moving faster than light should be going backwards in time, so in our time frame some of the oldest things we are viewing should be much younger by now!

[asprung]

I still come back to the point that the space man has but one body and if that contracts it could kill him. You seem to be saying that he in effect has two bodies and that since only the one in the other reference plane contracts he wont notice it.

[J.C.MacSwell]

I still come back to the point that the space man has but one body and if that contracts it could kill him. You seem to be saying that he in effect has two bodies and that since only the one in the other reference plane contracts he wont notice it.

 

You are in an infinite number of reference frames at near lightspeed.

 

How ya feelin'? No need to reply if you're dead.

[Sisyphus]

I think it's just a matter of getting used to the idea that length is not an absolute, but dependent on the system (reference frame) in which it is measured. This isn't a great analogy, but if you spin clockwise as seen from above, you're spinning counter clockwise from below. This doesn't mean there are two of you, or that you're spinning two directions at once and thus getting twisted into pieces, or that one statement has to be false or illusory. It's just different, depending on the orientation in which it is considered.

[swansont]

In one frame the astronaut is 2m tall. (Big for an astronaut, but this is just an example). In another, traveling such that gamma=0.5 with respect to the astronaut, he is 1m tall.

 

There is absolutely NO measurement that you can do that tells you which measurement is "correct." Measurement is reality, since there is no way to justify calling one measurement valid while excluding another.

[NowThatWeKnow]

But with relativistic velocities, it does shrink, in the applicable reference frames. It's not just an illusion, as with a mirror. A twenty foot pole moving fast enough will fit inside a ten foot room, in the reference frame where the room isn't moving...

I started a thread once called "Is relativistic mass an illusion" and got varied responses. What you observe from different frames will vary but no matter what frame your are in, 1' is 1' and you can not mix frames as you are suggesting above. I do agree the mirror may not have been the best analogy.

 

Interesting. I don't know, but I'm thinking it can't work the same way as motion, if only because at some point they'd all have infinite momentum, and then beyond...

 

Oh, and it's not caused by motion relative to the CMB. "At rest with respect to the CMB" is convenient but not privileged. It's caused by motion relative to whatever reference frame it's considered in.

 

Yes, motion relative to the CMB was not a good example but at that moment it seemed right since galaxies are basically at rest with the CMB despite separating at relativistic speeds.

 

Martin said any one at rest with the CMB, any where in the universe, would calculate the age of the universe the same. That indicates to me that there is no time dilation between separating galaxies (with the same background temperature). I would like someone with more knowledge then me to chime in here..................Please Maybe the uniform expansion is acceleration equal in all directions with time dilatation being equal accross the universe. Hang on, time is slowing down and will soon stop.

Edited May 9, 2009 by NowThatWeKnow

[asprung]

There seems little doubt that length contraction would actually occur within the spaceman’s ship and reference frame just as would a slowing of his clock. As the contraction would occur in only one direction the actual size would make no difference as there would be distortion which I would think could injure or kill.

[Mr Skeptic]

And yet you are not distorted and dead.