Does Lorentz contraction affect a stationary object that you pass at high speed?

  • 102 Replies
  • 33690 Views

0 Members and 1 Guest are viewing this topic.

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Lorentz contraction has been mentioned a few time in threads just lately. I understand that an oblect travelling at very high speed will contract along its length in the direction of travel.

Now, GR states that if 2 objects pass each other with nothing to reference against, it is impossible for a person on 1 of them to know whether it is the object he is on or the other 1 that is moving.

So, my question is, if I was in a spaceship travelling at relativistic speed and we passed a stationary object, would it appear to me as being contracted? Surely it must to fit in with GR. But if it is velocity that causes Lorentz contraction then it wouldn't affect a stationary ship, would it?
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline Vern

  • Neilep Level Member
  • ******
  • 2072
    • View Profile
    • Photonics
It is relative velocity that causes the length contraction. So the answer is yes. You would not be able to determine whether it was you or the object that was moving without some other reference. All motion is relative.

You get the same answer whether you calculate using the SR, GR, or Lorentz conventions. I like the Lorentz version because it doesn't require that we think of space and time as being distorted. All of the distortion can be attributed to the matter that moves. However, the Lorentz version is more complicated and requires a special frame of reference fixed in space.
« Last Edit: 20/03/2009 21:52:10 by Vern »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Thanks, Vern. I guessed it would look contracted but I wasn't sure.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
I think I can see where your thoughts went DB. Is the contraction real? And if it is a real one, and I know that I've been accelerating my ship and therefore have 'objective evidence' of me traveling very fast and then passes that other ship that, according to what we earlier agreed on, just would be standing still relative what frame of reference we both shared before this thought experiment. Will that ship be contracted 'for real' although we knew before whom it is moving faster, as we both had the same frame of reference originally (Earth).
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
yor_on:

I wasn't sure whether it was due to velocity per se or relative velocity. I guessed it was relative velocity as otherwise it would contradict GR.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.

You're trying to confuse me again. And succeeding.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.

You're trying to confuse me again. And succeeding.

[???] Think that I bieleved to clear things up!

What is unclear?
« Last Edit: 21/03/2009 18:48:50 by lightarrow »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Alberto - It's OK. I undertood it.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.

In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed.  Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed.  However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it  [;D]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
I got to admit that the question if the Lorentz contraction is a real process have been on my mind for quite some time. Those two links sees it as being as real as we see time dilation to be. http://arxiv.org/pdf/physics/0606171v1 as well as http://renshaw.teleinc.com/papers/simiee2/simiee2.stm

If it is so then I made this thought experiment wherein we have a predefined common nominator (Earth) that we start both ships from. One of them we will place being at rest with Earth, the other one will pass it accelerating to a near 'c'. They will measure each other (lasers) and will both find the other one shorter. Although we now already know that one of the ships are being at rest relative Earth and we also know that the other ship is accelerating through its creation of a 'gravity well' situated behind it we still will observe this phenomena? And it will be real?? If so,that implies that this goes for Earth to the same degree too, right?

Think now of the same system (two ships & Earth) with the exception that the formerly accelerating ship now have stopped its acceleration and are now in what we call 'uniform motion'. This mean that there is no longer any real proof of what speed or motion this ship might have, and even when looking out, there is no proof that it isn't the rest of the universe that is moving relative them instead of the other way around. But when they meet this ship again the same phenomena (Lorentz contraction) will be seen. What does this say about length? If we can't guarantee any motion as being any better than a 'preconception' based on arbitrary choices, isn't that the same as saying that our universe, depending on our choice of frame will have different sizes, also that this frame do not act only on you (accelerating ship) but also on the frame you compare it too (ship at rest versus Earth). It is a intriguing concept if it is not a optical illusion.

----

Expressed as Energy one could say that the ship accelerating are collecting a lot of 'relative energy' distorting spacetime. But the ship being at rest with Earth? They will see the same effect, yet, haven't collected or received any relative energy as I understands it. To see the strangeness here you must understand that, according to those ideas, both ships length contraction is real.

----
http://adsabs.harvard.edu/abs/2001APS..APR.C9001R
« Last Edit: 21/03/2009 21:55:09 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.

In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed.  Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed.  However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it  [;D]

Sometimes I really hate you!
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.

In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed.  Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed.  However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it  [;D]

Sometimes I really hate you!
Noo! If you think about what I wrote, you should grasp that the paradox comes from the wrong assumption that when you measure the lenght of the ladder (or the shed) the simultaneity is absolute, while instead is frame-dependent.
Another name for this paradox is "The barn and the Pole paradox":
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.

In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed.  Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed.  However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it  [;D]

Sometimes I really hate you!
Noo! If you think about what I wrote, you should grasp that the paradox comes from the wrong assumption that when you measure the lenght of the ladder (or the shed) the simultaneity is absolute, while instead is frame-dependent.
Another name for this paradox is "The barn and the Pole paradox":
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html

ohhh, let me hit him anyway.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Yeah, the barn and the pole is a nice example too:)
So moving/accelerating begets a shrinking universe from the frame of the one moving and for the frame 'not moving' the other ship will be the 'thing' shrinking. the first ships revelation could be explained by spacetime distortion, and what the other ships sees? Also a spacetime distortion? But if what the moving ship experience as 'shrinking' is a real effect, Then it seems to have no proportion to the energy being spent creating it. As, in fact, the whole universe reacts to this ships motion in time, and all for real. If this is true I can't help but wonder about how 'energy' transforms into 'work'.

------

If work is done on an object when you transfer energy to that object, then there has been no transfer of energy as far as I can see, still the universe have shrunk as has all objects in it, the thing bugging me is that it is 'real'?

So where is this concept defining how this can be? It's not any work done on the objects outside the ships frame of reference, it's only work done on 'space' and the ship while accelerating it, and that 'work' seems to go a long way :)
« Last Edit: 22/03/2009 11:38:15 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
Ouch, ouch, ouch, ouch!
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?

 [???]
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?

 [???]

If they are traveling at a uniform velocity and being 'at rest' when compared to each other they will belong to the same 'frame of reference' and there will be no Lorentz contraction seen between them. But if you are thinking of them accelerating at the same exact velocity? I guess they still could be seen as being 'at rest'? I don't really know, that's seems a tricky one DB.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline Vern

  • Neilep Level Member
  • ******
  • 2072
    • View Profile
    • Photonics
If you were considering them as a system from another frame they should seem to close the distance between them. Edit: and as yor_on indicates, from the same frame they would see no change.

This brings to mind something that just occurred to me. As most of you now know, I prefer the Lorentz description of relativity phenomena to the Einstein version. With Lorentz, length contraction of objects in motion is a physical distortion of the objects, and not a distortion of space and time as with Einstein. So far, there has never been an experiment that could test a difference in the two concepts. So, Occam's razor cuts out Lorentz.

Now, lets apply the Lorentz version to the scenario in the OP. My near-light-speed ship is passing a stationary ship. What is my perception of the length of that stationary ship? Einstein says I see it length contracted. What about Lorentz?

It seems now as I think about it, the Lorentz version where my measuring devices suffer the contractions, and the stationary ship does not, Lorentz should say the stationary ship seems expanded, not contracted.

There is a proposed test of this by a satellite containing a very precise measuring device that can measure the angle between two stars. The test proposal is that the speed of the earth in orbit is enough to change the apparent angle between two stars from one earth season to the next. If my thinking is right, the Einstein version would see the contraction. The Lorentz version should see no contraction.

The reason why is: Half of the effect is due to aberration, the other half, contraction due to earth's motion relative to the stars. Aberration and contraction are additive so produce double the calculated contraction with Einstein. Aberration and Lorentz expansion would cancel, so that no effect would be seen.

Edit: That last sentence should read: Aberration and apparent expansion due to Lorentz contraction of local measuring devices would cancel ....

Here's a link to the article about the test.
« Last Edit: 22/03/2009 15:56:47 by Vern »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?

 [???]

If they are traveling at a uniform velocity and being 'at rest' when compared to each other they will belong to the same 'frame of reference' and there will be no Lorentz contraction seen between them. But if you are thinking of them accelerating at the same exact velocity? I guess they still could be seen as being 'at rest'? I don't really know, that's seems a tricky one DB.

I meant to an outside observer.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Vern, when I read him I got the impression that he accepted length contraction as real, reading him again I see that he seem to doubt it by his conclusive words? But there is still the muon test wherein he writes "In the muon'sí frame of reference, the situation is quite different. The only way this can happen in the muon'sí reference frame is if the actual physical distance that must be traveled by them is shortened as in (8). This is not a visual effect for the muon. If the distance traveled by the muon is not physically shorter, the muon simply does not remain in existence long enough to make the trip, even at speeds greater than .9c. To the muon, length contraction is clearly not merely a visual effect, as the muon is not "seeing" anything. The distance to be traveled by the muon from the upper atmosphere to sea level is physically shorter than the same distance measured by a slower moving particle. The high speed muon performs Einsteinís train embankment experiment first hand."

I don't really know what to think here, in what way do you mean that this aberration cancels out Lorentz contraction? It seems to go both ways depending on the observer? ". The maximum amount of the aberrational displacement of a star is approximately 20 arcseconds in right ascension or declination. ".It seems to depend on the movement relative the observer? Or am I thinking wrong here?? http://en.wikipedia.org/wiki/Aberration_of_light#Apparent_and_true_positions
« Last Edit: 22/03/2009 19:51:35 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Ok DB, got it.
And again, I don't know :)
The difficulty here seems to be to decide what the 'system' observed consists of. Is it only the material objects that we will observe this phenomena on or should space between them be included. If one consider the 'muon description' it definitely seem to consider 'distance' in itself so considering this I would expect it to have an effect on the space surrounding those two objects. Even if space is 'empty' of matter it still can contain a 'distance', but is that space moving? Shouldn't it be seen the same way as the observer? as relative the moving ship containing non moving 'static points' in spacetime? This one is sooo strange to me :) Lightarrow et al, give it a shot. There is definitely at least two 'camps' of reasoning here, if not more?? http://www.physicsforums.com/showthread.php?t=106526 and no one seems totally 'wrong'. The muon example seems like a reasonable proof to me as we have proofs for time dilation and this one, according to what I understands (not much:), is similar..
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline Vern

  • Neilep Level Member
  • ******
  • 2072
    • View Profile
    • Photonics
Hi yor_on; I agree that Curt Renshaw, in the link, has some notions about the cause of the Lorentz contraction that is at odds with what most of us suspect. But he does describe the proposed experiment that would see a difference between the Lorentz version of space-time and the Einstein version IMHO.

Yes; the muon must see the distance shortened as well as the time dilated in order to reach the earth's surface as a muon. I haven't thought about this enough to understand if it rules out the Lorentz version.

The referenced experiment was supposed to take place in 2005. I wonder what the results indicated. A positive result would support the Einstein version, a negative result would support the Lorentz version -- but it wouldn't rule out Renshaw either.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
I have a link saying that the experiment should start 2008.
http://adsabs.harvard.edu/abs/2001APS..APR.C9001R but I've found no conclusions drawn from it on the 'net yet' njet :)) :  (<--- Lorentz contracted smiley:)

I've such a bad sense of humor..
My doctor told me it was to late to cure too.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline Vern

  • Neilep Level Member
  • ******
  • 2072
    • View Profile
    • Photonics
Thanks for the link yor_on. If it did start in 2008, someone should have results by now. But this in one of those cases where a positive result would be announced right away. A negative result may never be reported [:)]

 

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?

 [???]
Of course.
If you travelled at very high speed(*), you would measure all distances between points (which are moving with respect to you) as contracted, independently where those points are (in matter or in the void). At very high speed, not only you would measure all bodies, example planets and stars, as "compressed" in dishes, but also theire distances would be so. In a few seconds (or more or less, according to your speed) you could travel along all the universe.

(*)Of course the same if bodies travelled and you were still, there is no difference, what counts is relative motion.
« Last Edit: 22/03/2009 20:37:13 by lightarrow »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
You've touched on what I was wondering. Would that be a way for us to see what is outside our visible universe? If we were travelling at relativistic speed, the distance between us and the visible horizon would be less. Does the contraction mean we could see past it or would time dilation rear its ugly head and prevent it?
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
You've touched on what I was wondering. Would that be a way for us to see what is outside our visible universe?
Certainly, you would be able to go everywhere in the existing universe, visible or not.
Quote
If we were travelling at relativistic speed, the distance between us and the visible horizon would be less. Does the contraction mean we could see past it or would time dilation rear its ugly head and prevent it?
The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.
« Last Edit: 22/03/2009 23:04:22 by lightarrow »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Thank you, Alberto.

Is there a limit to the amount of contraction or is it another 1 of those horrible infinity things? At c, does everything have zero length?

You see, there was another side to this that I was wondering about and that's why I mentioned time dilation. If you could travel at, say, 0.99c, how much contraction would there be between you and the horizon of the visible universe? Or does contraction only apply when you pass someting?

Here's what I was puzzling over. In our frame of reference here on Earth it has taken light 13.7 billion years to get here. Now, nothing can travel faster than c and in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate. So, it should take you more than 13.7 billion years to get there by your own timescale. But, if the distance is greatly contracted then at 0.99c it may take you less than 13.7 billion years to get there. That can't be right.

The only solution I can see is that time dilation must come into it somehow but I can't figure out how because in your own frame of reference there shouldn't be any. Or is there something else that I'm missing completely?
« Last Edit: 24/03/2009 01:18:16 by DoctorBeaver »
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
Thank you, Alberto.

Is there a limit to the amount of contraction or is it another 1 of those horrible infinity things? At c, does everything have zero length?
Yes.

Quote
You see, there was another side to this that I was wondering about and that's why I mentioned time dilation. If you could travel at, say, 0.99c, how much contraction would there be between you and the horizon of the visible universe?
Sqrt(1 - 0.992) ~ 0.14, so 1km --> 0.14km.

Quote
Or does contraction only apply when you pass someting?
No, always.

Quote
Here's what I was puzzling over. In our frame of reference here on Earth it has taken light 13.7 billion years to get here. Now, nothing can travel faster than c and in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate. So, it should take you more than 13.7 billion years to get there by your own timescale.
Haven't understood this one.

Quote
But, if the distance is greatly contracted then at 0.99c it may take you less than 13.7 billion years to get there. That can't be right.
Why? You get there in 13.7*0.14 = 1.92 billion years.

If you want to get there in 1 year (for example), you should travel at:
0,9999999999999999999999733603282c.

Quote
The only solution I can see is that time dilation must come into it somehow but I can't figure out how because in your own frame of reference there shouldn't be any. Or is there something else that I'm missing completely?
Can't grasp your actual concern.

Edit: I made a slight mistake in my previos computation of the time you need to get there; actually is 1.92/0.99 = 1.94 billion years.
« Last Edit: 24/03/2009 20:05:19 by lightarrow »

*

Offline dlorde

  • Neilep Level Member
  • ******
  • 1452
  • ex human-biologist & software developer
    • View Profile
... in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate.
Consider what this actually means. What would you expect to see if this was not true?

You can look out to other frames of reference and see them running fast or slow by your watch, but time is always going to be uniform in your own frame of reference, so it can only run fast or slow relative to another frame. You will always see your watch running at the same rate, whatever happens, because if time slows or speeds up (relative to an external frame) for your watch, it slows or speeds up for everything else in your reference frame, including your physiology, the operation of your brain, etc.

If that's not what you meant, I'm curious to know what you did mean.

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
dlorde - That is precisely my point.

Alberto - You said "You get there in 13.7*0.14 = 1.92 billion years.".

From the point of view of someone on Earth, it has taken light 13.7 billion years to make the journey. From the perspective of someone travelling at 0.99c light would still be travelling at c relative to him (basic GR). Therefore, to him light would still take 13.7 billion years to travel that same distance. Am I right so far?

If so, then it follows that he cannot possibly cover the same distance in 1.92 billion years in his own frame of reference. To do so he must travel at 13.7/1.92 = 7.14c. How does that resolve?

 
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
dlorde - That is precisely my point.

Alberto - You said "You get there in 13.7*0.14 = 1.92 billion years.".

From the point of view of someone on Earth, it has taken light 13.7 billion years to make the journey. From the perspective of someone travelling at 0.99c light would still be travelling at c relative to him (basic GR). Therefore, to him light would still take 13.7 billion years to travel that same distance. Am I right so far?
No, because the distance is smaller. Let's say that at 13.7 billion light years (limit of visible universe) there is a quasar which name is "Q" and that from there a beam of laser light is sent in direction Earth at the moment of your passing close to Earth, in direction Q, with your starship, at 0.99c. Inside your starship you measure as distance from you and Q:  1.92 billion light years. How long will something travelling at c take to reach you? time = space/velocity = 1.92 billion light years/c = 1.92 billion years, so you would receive the beam of laser light in 1.92 billion years.
« Last Edit: 24/03/2009 20:32:18 by lightarrow »

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth? The visible edge would no longer be 13.7 billion years * 300,000km/sec distant?

How far does the contraction go? From the photon's perspective, would the distance be zero?
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth?
No, to reach *you*.

Quote
The visible edge would no longer be 13.7 billion years * 300,000km/sec distant?
You should have written 13.7 billion years * 1 light year/year = 13.7 billion light years, however it wouldn't be that distance anylonger *for you*;  for Earth would be the same.

Quote
How far does the contraction go? From the photon's perspective, would the distance be zero?
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth?
No, to reach *you*.


But, surely, you would see the distance between the edge and Earth contracted therefore light would travel that distance in less than 13.7 billion years.

Quote
Quote
How far does the contraction go? From the photon's perspective, would the distance be zero?
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.

My brain is going to hurt again now. I just know it.

OK. So at (near)c distance reduces to zero. Therefore it must take zero time to get anywhere as everywhere would be in the same place but of zero length. That sounds like a singularity to me  [???]

Would you yourself be contracted to zero size? If not, how could you fit there? And if it is only length that is contracted, does that mean that everything becomes 2-dimensional? I don't like the thought of that.
« Last Edit: 24/03/2009 21:07:55 by DoctorBeaver »
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
No, to reach *you*.
But, surely, you would see the distance between the edge and Earth contracted therefore light would travel that distance in less than 13.7 billion years.
Yes, but while *in your frame of reference* light will meet Earth in 1.92 b.y., *in the Earth frame* it'll be 13.7 b.y.

Quote
Quote
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.
My brain is going to hurt again now. I just know it.
OK. So at (near)c distance reduces to zero. Therefore it must take zero time to get anywhere as everywhere would be in the same place but of zero length. That sounds like a singularity to me  [???]
Infact it's even for this reason that the photon's perspective doesn't exist  [:)].  If you talk about "near c", instead, then distances and time intervals of travels are not zero, even if as little as you want, approaching c.

Quote
Would you yourself be contracted to zero size?
You wish it was!  [;)].  Apart from jokes, from your frame of reference in the starship, everything and of course everyone moving with respect to you would be contracted, not yourself (but you would be contracted *for them*).

Quote
If not, how could you fit there? And if it is only length that is contracted, does that mean that everything becomes 2-dimensional? I don't like the thought of that.
Yes, the "thickness" in the direction of movement would tend to reduce to zero so everything would become bidimensional. You don't like it? But do you realize that you need almost an infinite amount of energy to reach almost c? It's not just to push on the accelerator...

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
In fact that is one of the most confusing truths I know of Lightarrow:)
And a very nice description/discussion btw.

We know that a photon at all times moves at 'c' (depending on density:)
We also know that it has a 'duality' (light 'matter')

Therefore, from the perspective of that photon, on one hand I could say that it both encompass all 'time' there ever has been, as well as say, ah, on the other hand, that it has no 'time' at all as it doesn't really exist in 'time'. Encompass all 'time' as that very first one, if seen as a particle :) would should and will see our universe die, or rather, not even notice it at all from its birth to its death. I love it ::))

On the third hand though :) it's photons that interact with us all, from the ones showing of 'at' our atoms to the ones we can see ((you've already heard that we can see a photon I presume :) Is that a true statement btw?:)

And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.

----

If you like, thinking of that very first photon coming into 'existence' you could ask yourself if there could exist any more photons as seen from the perspective of that first one, where would they take 'place'?
« Last Edit: 25/03/2009 00:13:28 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Quote
And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.

Which is something I was getting to. I was taking it 1 step at a time to make sure I was thinking correctly.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12351
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Ouch DB, sorry, my only defense would be that the questions you state are similar to my own:)
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
It's only a mathematical limit, you will never be able to reach exactly c, so why do you worry about it exactly?

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
Quote
And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.

Which is something I was getting to. I was taking it 1 step at a time to make sure I was thinking correctly.

One possible way of interpreting it is that what we view as the photon's movement through space seems, to the photon, to be it's movement through time; the photon doesn't think it's moving through space at all but believes it's stationary (that's if a photon were to have any awareness, of course).
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
It's only a mathematical limit, you will never be able to reach exactly c, so why do you worry about it exactly?

OK, forget zero size. Their effective size can be altered by velocity. I find that troublesome.
« Last Edit: 25/03/2009 22:15:51 by DoctorBeaver »
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
OK, forget zero size. Their effective size can be altered by velocity. I find that troublesome.
Why?

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
I just don't like the thought of it. It just seems wrong. I want to punch it.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
I just don't like the thought of it. It just seems wrong. I want to punch it.
What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).

It's not that it's difficult for me to accept that space & time are not rigid structures. I understand warping & contraction of space, and its implications, due to gravity. My problem is getting to grips with the notion that distances can get shorter as we move faster. I know the difference would be immeasurably small, but if I walk somewhere it will be further than if I drive there at 100mph.

I fully accept time dilation and I don't have a problem with that as I more-or-less understand the reasoning behind it. But I don't understand contraction of distance in the same way. Maybe if I did I would feel happier about it.
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

*

Offline lightarrow

  • Neilep Level Member
  • ******
  • 4586
    • View Profile
What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).

It's not that it's difficult for me to accept that space & time are not rigid structures. I understand warping & contraction of space, and its implications, due to gravity. My problem is getting to grips with the notion that distances can get shorter as we move faster. I know the difference would be immeasurably small, but if I walk somewhere it will be further than if I drive there at 100mph.

I fully accept time dilation and I don't have a problem with that as I more-or-less understand the reasoning behind it. But I don't understand contraction of distance in the same way. Maybe if I did I would feel happier about it.
As i tried to explain (probably I didn't succeed  [:)]) it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points: you have to measure the two points positions *simultaneously*. To do this, the points have to send their position information to the experimenter, and this is done with light, which has not an infinite speed, so these informations don't arrive simultaneously to a moving experimenter, if they arrive simultaneously to an experimenter at rest. For this reason their distance is not the same anylonger. Don't know if you now grasped something.

*

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • 12656
  • A stitch in time would have confused Einstein.
    • View Profile
Alberto - I'm just getting more confused now.

Look at this quote:

The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.

Your reply states (where I've highlighted it) that the distance would be less yet now you are saying that it is the way that distance is measured that makes it seem less:

Quote
it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.