The Naked Scientists

The Naked Scientists Forum

Author Topic: Does Lorentz contraction affect a stationary object that you pass at high speed?  (Read 33299 times)

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
I just don't like the thought of it. It just seems wrong. I want to punch it.

Lol

Try thinking in terms of that summed-vector view I've mentioned in a couple of threads.  In that interpretation, everything is always traveling at 'c'.  However, that constant speed of 'c' is a sum of two vectors and while the product of the two vectors is an absolute, the individual vectors, representing space and time, aren't.  Space and time then, can be any value, as long as they sum to the absolute value 'c'.  I think that what makes this counter-intuitive is that it seems the other way around to us; it is space and time that appear to be constant, which it is, but only from our point of view, which is dictated by the summed vector.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • 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
I put the word "artefact" in commas because it's not a real artefact, but the reality; Writing that way I just wanted to point out that it's a relativistic effect, that is it's due to how we define distance, which depends on the frame of reference. Maybe it's this that you aren't grasping: our definition of distance is frame-dependent, it's not an *intrinsic* property of bodies or of space.
« Last Edit: 26/03/2009 19:38:11 by lightarrow »
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • 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
I put the word "artefact" in commas because it's not a real artefact, but the reality; Writing that way I just wanted to point out that it's a relativistic effect, that is it's due to how we define distance, which depends on the frame of reference. Maybe it's this that you aren't grasping: our definition of distance is frame-dependent, it's not an *intrinsic* property of bodies or of space.


I want my mummy!
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Let me go away & have a think.
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
I want my mummy!

I always loved the Rolf Harris version of that song  :D
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
If 'distance' is a property of 'frames', where are we?
Once 'we' were an idea inside a cave looking out. Now we are 'out' of that cave, but we still need to define what 'distance' is. If we can't define 'rest', and can't define 'distance', as anything more than a relation between 'two frames of reference' we shouldn't expect space to have any recognizable' property's except those we need to define ourselves in it :) And that, in fact, just create the same dilemma as when we once saw the the sun as movóng around us.

So, what conclusions can we draw from this statement? Only this, that what we can test by repeatable experiments under controllable circumstances will be the 'inclinations' toward what spacetime possibly is. That doesn't say that we can't speculate, it just mean that spacetime seems like something not applicable to Newtonian standards, and that means those 'standards' that we see as applying 'locally' macroscopically for us.

 

Offline Vern

  • Neilep Level Member
  • ******
  • Posts: 2072
    • View Profile
    • Photonics
Quote from: yor_on
So, what conclusions can we draw from this statement? Only this, that what we can test by repeatable experiments under controllable circumstances will be the 'inclinations' toward what spacetime possibly is.
IMHO this is about as close as we can get to reality. We can measure and guess. And if we continue as in the past; we will guess wrong the first few times. :)
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
I would define 'distance' as: The measure of difference between two values.

The actual distance measured can be dependent upon upon your frame of reference though, so two different frames of reference may measure two different distances.

I think that part of the problem we're discussing is that it's impossible to measure what we're trying to measure in the way that we're trying to measure it.  For example, if we measured the length of something in terms of the angular difference between it's two ends, it's length would vary according to how far away it was from us; "These are small... but the ones out there are far away. Small... far away... ah forget it!" - Father Ted
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Quote
"These are small... but the ones out there are far away. Small... far away... ah forget it!" - Father Ted

Classic!  :D
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.
 

Offline Vern

  • Neilep Level Member
  • ******
  • Posts: 2072
    • View Profile
    • Photonics
I'm still wrestling with the concept of Lorentz space-time vs Einstein's SR. Now I see how the length of a stationary object must be contracted when moving past it even with the Lorentz version. I forgot that time is also dilated for the moving vessel. That means it would pass the stationary vessel in less time, and so would measure its length as contracted. So the situation is the same.
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.

Ah - no.  In any measurement, a difference is a difference.  And that's what it really comes down to; we can move stuff around, to make the difference look different, from different points of view, but at the end of the day there's a difference that needs to be accounted for.  You can't just shrug it off as imaginary.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
That is the 'funny' thing about it, ain't it? It's a 'difference of positions, measured simultaneously.' we are used to see 'distance' as something needing only one observer to be 'true'. LeeE described 'father Ted' here :)

Still, that ain't the whole 'truth' as i see it, as long as we have a 'depth perspective' to measure something in we trust in that, what I see and what you see, if different, will be explainable as consisting of being measured from different distances. But that has nothing to do with Lorentz contraction as I see it.

If it is a 'real' situation with length being dependent on the relative motion as measured between two 'frames of reference' then distance is a questionable thing to me.
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
Perspective only works in flat space.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.

Ah - no.  In any measurement, a difference is a difference.  And that's what it really comes down to; we can move stuff around, to make the difference look different, from different points of view, but at the end of the day there's a difference that needs to be accounted for.  You can't just shrug it off as imaginary.
Sorry, but I haven't grasped what you mean.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Just me thinking of the analogue with 'father Ted' :)
I see Lorenz contraction as something different than angular problems of distance. To me it questions the whole idea of 'distance' whatsoever if it is real.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
You introduce a interesting question there Lightarrow.
Can one isolate f ex. time from 'spacetime' and say that it is time that change the measurements?
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.

Spatial distance can be defined without needing to reference temporal distance.  In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining.  For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time.  However, it may measured as being a different length depending on the frame of the measuring observer.

The difference between the observed relativistic temporal and spatial effects when such an object closely approaches a BH and then returns to a distant observer are that the spatial length can be reconciled but the temporal durations can't i.e. the ruler is the same length as it was before, but it's now younger than the observer.  Hmm...  have I crossed topics here?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.

Spatial distance can be defined without needing to reference temporal distance.  In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining.  For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time.  However, it may measured as being a different length depending on the frame of the measuring observer.
As to say: "it's red, unless it isn't"  :)
To define distance you have to measure positions of points at specific times; imagine a spring which is slowly extending: now it's 1 metre long, after 1 hour is 1.001 metres, ecc. Which is its lenght? You can't avoid using the concept of time.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Some statements, you tell me if and where you disagree :)

The universe have general macroscopic properties as 'Time' and three 'spatial dimensions'. Inside them we find matter and vacuum and light. Matter and vacuum (space) are defined in/as density and distance. A perfect vacuum is defined as containing no matter nor mass nor density. Distance is defined as being a property relating to what frames of reference we use to compare and measure it with.

Light is measured as a invariant velocity in a vacuum over a certain distance in time. It is also thought to consist of 'light quanta' of a invariant energy amount. Light will always be 'time less' no matter how much it is 'slowed down' as seen from another frame of reference. It is also seen as a 'duality' in that we have experiments proving it to act as a particle as well as waves. Photons in QED (Quantum Electro Dynamics) are seen as both 'real' photons existing in a continuum in measurable time (Sun Earth) and as 'virtual' photons 'surrounding' atoms and outside measurable time.

Those virtual photons is expected to be responsible for the forces of electricity and magnetism. and also (?) seem to be the carriers of all other 'communication' between particles? A perfect Vacuum, although empty of 'matter', have a hidden 'energy' as well as consisting of virtual particles. Those interact with our macroscopic spacetime although they themselves are of to short duration to become measurable according to HUP (Heisenberg's Uncertainty Principle) and Planck time. So what do we have?

Light/photons/waves acting in a twofold manner, as measurable light and as unmeasurable light, 'timeless' internally but obeying spacetimes geodesics and able to act 'in time' on our universe, existing as a needful property for both living as well as dead matter. A vacuum devoid of matter (if perfect) but not of energy and virtual particles, and also containing 'distances'. Matter which I 'split' in two parts, 'living' and 'dead'.

So what else have I forgotten here?
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.

Spatial distance can be defined without needing to reference temporal distance.  In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining.  For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time.  However, it may measured as being a different length depending on the frame of the measuring observer.
As to say: "it's red, unless it isn't"  :)
To define distance you have to measure positions of points at specific times; imagine a spring which is slowly extending: now it's 1 metre long, after 1 hour is 1.001 metres, ecc. Which is its lenght? You can't avoid using the concept of time.

I can't quite see what point you're trying to make here.

You've quoted me as saying "Spatial distance can be defined without needing to reference temporal distance.  In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining", which I thought made the difference between defining and measuring pretty clear, but then you say "To define distance you have to measure positions of points at specific times", which is just plain incorrect; you can define something without needing to measure it.  If I define something to be 30cm long then measuring it is redundant - it is by definition 30cm long.

I also don't understand why you've also highlighted the next bit of text where I say "For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time" and then go on to talk about a spring that is explicitly changing over time: how is it relevant to compare something that explicitly doesn't change over time with something that explicitly does?

Quote
You can't avoid using the concept of time

The concept of time?  Well, I guess that with something that doesn't change over time, the concept of time is relevant, but only by virtue of time being specifically excluded as a factor.

When a state changes, yes, time is a factor, but where there is no change of state time is not a factor because the state is constant and there is no change of state over time;  any formula that tries to link the state S with time t isn't going to work because a change in t is not reflected by a change in S.  Indeed, in any such formula, t must be meaningless for any value of t if S is to remain unchanged.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?
« Last Edit: 31/03/2009 18:53:40 by lightarrow »
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?

Physics is a sub-set of philosophy and at the level we're discussing physics, dealing with abstracts is part of the deal.  Are you discussing engineering or physics?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?

Physics is a sub-set of philosophy and at the level we're discussing physics, dealing with abstracts is part of the deal.  Are you discussing engineering or physics?
Can you show me a (serious) book of physics where it's written that you can *define* a distance between two points without having to measure it, apart the sample metre, of course?
« Last Edit: 31/03/2009 19:23:48 by lightarrow »
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums