Can a spaceman survive length contraction?

[NowThatWeKnow]

...(and possible injured) .... What I can’t comprehend is how the single body of the spaceman can be both compressed and not compressed...

I know that many will argue that length contraction is not an illusion but maybe the distorted mirror may be the best way for some to look at it.

[asprung]

From swansont's post I seem to have it backwards. If the length contraction is observed by the spaceman it occurs in his frame and he could be injured.

[NowThatWeKnow]

From swansont's post I seem to have it backwards. If the length contraction is observed by the spaceman it occurs in his frame and he could be injured.

The space mans frame is his rocket ship and all that is in it. It all looks normal to him. He is not hurt. When the space man looks out the window, he is looking at a different frame that is contracted from ONLY his point off view.

 

Edit - I think your problem is where to place the borders of each frame.

[iNow]

The only contraction the spaceman will view is going to be in some other frame of reference. As has been noted previously, he does not notice nor experience contraction of or in his own frame.

[asprung]

Then I had it right,swansont backwards?

[NowThatWeKnow]

Then I had it right,swansont backwards?

I do not see where swansont is backwards. A lot has been said (repeated) and you should use quotes around the text you are talking about. What you are thinking may be clear in your mind but not to the rest off us.

[D H]

From swansont's post I seem to have it backwards. If the length contraction is observed by the spaceman it occurs in his frame and he could be injured.

You have it backward, twice around. The spaceman sees the Earth as being subject to length contraction. He sees himself as the same height he has always been. People on the Earth see the spaceman as being subject to length contraction. They see themselves as the same height they have always been.

[swansont]

I apologize for trouble I may have caused. I fully understand that according to SR, when viewed from earths frame, the spaceman will be velocity compressed (and possible injured) but in his own frame everything will be normal. What I can’t comprehend is how the single body of the spaceman can be both compressed and not compressed. Do we just have to have faith in SR or does someone have an explanation?

 

Nobody will be injured from relativistic effects.

 

All of this is a consequence of the speed of light being a constant in all frames — length and time are not invariant quantities, i.e. it depends on who is making the measurement. You cannot say an astronaut is 2m tall, and you cannot say a certain amount of time has elapsed. You can only make those statements as someone in a particular frame of reference. The values will be different to someone in another frame.

 

Since the physics works exactly the same in all of these frames, each observer can claim they are at rest, and everyone not in that frame are the ones who are moving. No frame of reference can lay claim to the "real" value of any of these measurements.

 

Things moving relative to you are length-contracted. Clocks moving relative to you run slow. They will say the exact same thing about you. How much the lengths contract and how much time dilates depends on the relative speed.

[asprung]

1-Is there actual physical length contraction?

2-Is it only viewed from frames outside the spaceships frame such as earths?

3-Does it have any effect on the spacman?

[Klaynos]

1. Yes, if viewed from any moving frame relative to the spaceman.

2. Yes, the spaceman would also see length contraction in their frames from his.

3. No.

[asprung]

If the length contraction occurs but has no effect what does it do?

[Klaynos]

In his frame, nothing, as he is at rest in his own rest frame.

 

In another frame that he is not at rest in, it contracts him.

[Mr Skeptic]

1-Is there actual physical length contraction?

2-Is it only viewed from frames outside the spaceships frame such as earths?

3-Does it have any effect on the spacman?

 

1 - Yes, from a reference frame in which he is moving (ie, not his own)

2 - Correct, the spaceship is not moving in his own reference frame, but is in others'.

3 - Yes and no. Anyone measuring the spaceman from a different reference frame will measure him differently, but the spaceman will notice no difference in his own reference frame since he is not moving in his own reference frame.

 

You can consider the distortion real or illusionary depending on how you take your measurements. Consider that when you are moving, if you put a meterstick next to spaceman and measure him, you will say he is distorted. Spaceman will say that you moved toward the photons leaving the front of the meterstick and away from the ones at the back of the meterstick and furthermore didn't measure the front and back at the same time, so of course you got it wrong. See

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

[swansont]

1-Is there actual physical length contraction?

 

This suggests that you think there is some "real" length, and then the object gets crumpled, like it's a mechanical effect. That's not how it works.

 

I have an object, which I measure to be 1m long. Another observer, moving with respect to it, measures it to be 0.7m long. Yet another observer, moving even faster relative to it, sees it as 0.5m long. All the while, I am standing next to it and nothing is happening.

 

What is the length of the object? That question has no validity. One must specify the frame in which you are measuring the object.

 

Klaynos correctly said it was a physical effect, but I don't think you mean physical the way he did. It is not a mechanical effect, just as a clock slowing from time dilation is not due to some defect in a clock. It is not a mechanical compression. It is "simply" that length is not preserved when you transform to another frame of reference. Much like how kinetic energy does not transform, but less intuitive.

[asprung]

Length contraction without a corrosponding contraction of the other dimensions will lead to distorton which should be appearent without regard to size. I take it that the view is that this would not cause damage because it is not viewed in the frame of the spaceman. This takes me back to where I was at post #50.

[Klaynos]

I think this comes down to a difficulty that a lot of people experience when they are first taught about relativity. How can something contract in one frame and not in another? There's not much we can say, other than that's the way the universe is, it's got no obligation to be easily understandable by us...

[J.C.MacSwell]

Length contraction without a corrosponding contraction of the other dimensions will lead to distorton which should be appearent without regard to size. I take it that the view is that this would not cause damage because it is not viewed in the frame of the spaceman. This takes me back to where I was at post #50.

 

The distortion is the natural shape of the object viewed from a chosen frame at significant relative velocity. Any lack of distortion, would be cause for alarm. That could lead to the spaceman's death.

 

Beware the spaceman speeding by at relativistic speeds yet apparently undistorted.

 

He is considerably "stressed".

[Kyrisch]

I love how asprung has insidiously gotten us all to adopt the word 'spaceman' into our lexicon...

[asprung]

I see the difficulty in comprehending how the SAME thing can be contracted in one frame whlie not in another.

[Kyrisch]

I see the difficulty in comprehending how the SAME thing can be contracted in one frame whlie not in another.

 

That's an issue of the conceptualisation of the principle of relativity, and not any particular explanation in general is going to help you. It's all based on the idea that the speed of light is the same in all frames of reference, such that a light beam emitted from the headlight of a car will be going at the speed of light relative to an observer on the ground as well as relative to the driver of the car, unlike a classical object like a ball which would appear to be traveling faster relative to the observer at rest. All other aspects -- time dilation, length contraction -- are logical consequences of that single principle.

[asprung]

Are you saying that the speed of light is an example as to why we cant apply logic or is there some relationship I am missing. I am trying to understand,nothing more.

[iNow]

If I throw a ball to the East at 10 kph, then relative to me, a stationary observer, the ball is moving 10 kph.

 

If I'm on a train traveling east at 50 kph, and I throw the ball eastward at 10 kph, then relative to me the ball is traveling at 10 kph, but relative to a stationary observer on the ground (watching the train go by) the ball is traveling 60 kph to the east, because the velocities add. They see the train going 50 kph plus the ball going 10kph (relative to me) and think the ball is actually going 60 kph.

 

 

This is not what happens with light. If light is shined eastward from the ground it is going c.

If light is shined eastward from the train moving east, it is still going c, to both me AND the person on the ground.

If light is shined westward from a train moving east, it is still going c, to both me AND the person on the ground.

 

Unlike with the ball, the person on the ground does NOT see light moving faster when it's shined from the train.

 

The speed of light is invariant. It is counter intuitive, but that's the way it is. It is the invariance of the speed of light which dictates the dilation effects of time and length which we keep discussing, and how those concepts of time and length are completely dependent on the frame of reference, not available as some absolute or universal constant.

[asprung]

Thank you. One more stupid question. If length contraction only occurs when viewed from an outside frame why is this not true with respect to time ie why would the spaceman only age slower when viewed from an outside frame?

[swansont]

Thank you. One more stupid question. If length contraction only occurs when viewed from an outside frame why is this not true with respect to time ie why would the spaceman only age slower when viewed from an outside frame?

 

He does only age slower when viewed from an outside frame, as long as he stays in that frame. But once he accelerates, he changes reference frames.

[Bob_for_short]

for copying-and-pasting

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