length contraction experiment?

[Ras72]

?Hi,Has ther ever been an experimental verification of length contraction?

Thank You

[swansont]

?Hi,Has ther ever been an experimental verification of length contraction?

Thank You

Yes. Cosmic-ray muons have been detected to travel further in our frame than their rest-frame lifetime indicates they should; in their frame this is consistent with the length being contracted. Also, relativistic particle collisions obey as if the nuclei have been length contracted.

[ajb]

There has been no direct experiment observing the length contraction of a macroscopic object. However, as swansont has said, there is indirect evidence such as the decay of cosmic rays and particle collider experiments. These and any other experiments that directly or indirectly support special relativity all support the notion of length contraction. To date there are no consistent and repeatable experiments that do not agree with relativity.

[Ras72]

I looked at the muon experiment and it seems to me that it proves time dilation while length contraction is inferred from the formulation of Relativity.I guess you must have heard it a zillion times before but that leaves open the possibility that that particular prediction be wrong except of course that if it is it must be so that all other predictions, directly verified, would also result true no easy task

[imatfaal]

As mentioned above the results of relativistic heavy ion collisions can only be satisfactorily modelled when the ions are considered to be length contracted on collision

[IM Egdall]

More detail on accelerator experiments and testing length contraction: "a spherical bunch of particles coming at you looks like a flattened ellipsoid due to relativistic shortening, and the detection probabilities and expected directions of ejecta are affected." Physicists must take this into account in their experiments. REF: SelfAdjoint Mar 9, 2004 07:08 PM. See My link

 

Also "coulomb attraction between a stationary electron and a stationary proton are judged to increase when viewed from an inertial frame that moves in the direction of separation" (Ref: Relativity: Special, General, and Cosmological, Oxford University Press, 2001).

Edited October 19, 2011 by IM Egdall

[Ras72]

Is the predicted length contraction due to space contracting? IF so the trajectories of all photons would also be warped Wouldn't that make it impossible to directly observe length contraction?

[imatfaal]

Ras - these are lead ions that are being smashed into each other not photons.

 

Within their rest frame we model the ions as spherical - when two ions are on a collision course at close to c then whatever frame used at least one of the ions is travelling damn close to c and is thus length contracted, we must include this in any predictions of how they collide. This has nothing to do with observing or measuring a length contracting - but it has to do with the fact that if you model the collision as two spherical ions colliding you do not get the right results - if you model as two length contracted pancake shaped ions then then you do get the right results (ie your model give same results as the experiment)

[Ras72]

Ras - these are lead ions that are being smashed into each other not photons.

 

Within their rest frame we model the ions as spherical - when two ions are on a collision course at close to c then whatever frame used at least one of the ions is travelling damn close to c and is thus length contracted, we must include this in any predictions of how they collide. This has nothing to do with observing or measuring a length contracting - but it has to do with the fact that if you model the collision as two spherical ions colliding you do not get the right results - if you model as two length contracted pancake shaped ions then then you do get the right results (ie your model give same results as the experiment)

 

I understand about the particles in the particles smashing experiments .I was refering to measuring length contraction directly for a macro object If it is warping space shouldn't it be impossible to detect through photons or any other EM radiation?

[IM Egdall]

I understand about the particles in the particles smashing experiments .I was refering to measuring length contraction directly for a macro object If it is warping space shouldn't it be impossible to detect through photons or any other EM radiation?

 

 

Here is what I have read on length contraction of macro objects.

 

In 1959, James Terrell of Los Alamos Scientific Laboratory explained that though length contraction is the actual effect, it is not at all what we observe. He predicted that for astronomical observations (where the incoming light is essentially parallel), objects actually appear rotated due to relativity effects. Why? Because we do not see all the light rays from the object at the same instant in time, thus the object appears rotated.

 

See link: http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/ContractInvisible.html

[imatfaal]

IME

 

nice link - am I right in thinking if the light we viewed was simultaneous in emission (ie we saw a very short flash) we would see it as contraction - but as the light we see is, de facto, simultaneous in observation we see the rotation

 

I understand about the particles in the particles smashing experiments .I was refering to measuring length contraction directly for a macro object If it is warping space shouldn't it be impossible to detect through photons or any other EM radiation?

 

If you are a talking warping space - ie non-flat local spacetime - then I think SR is not what can be used. Hopefully someone can confirm but I believe a prerequisite for SR is locally flat spacetime; SR is a special limiting case of GR in flat minkowski space.

Edited October 21, 2011 by imatfaal

[DrRocket]

There has been no direct experiment observing the length contraction of a macroscopic object. However, as swansont has said, there is indirect evidence such as the decay of cosmic rays and particle collider experiments. These and any other experiments that directly or indirectly support special relativity all support the notion of length contraction. To date there are no consistent and repeatable experiments that do not agree with relativity.

 

There is a direct experiment being planned. It is at least a couple of years out. I do not have any details, but have been in intermittent contact with one participant on another forum. The group is not saying much.

[Ras72]

If you are a talking warping space - ie non-flat local spacetime - then I think SR is not what can be used. Hopefully someone can confirm but I believe a prerequisite for SR is locally flat spacetime; SR is a special limiting case of GR in flat minkowski space.

Evidently SR is less of a special case than Einstein thought; uniform motion also contracts space.What are the opinions on this? Is the uniform motion space contraction explanation prevalent?

 

 

 

[DrRocket]

Evidently SR is less of a special case than Einstein thought; uniform motion also contracts space.What are the opinions on this? Is the uniform motion space contraction explanation prevalent?

 

 

 

 

 

Uniform motion between inertisl reference frames in SR results in differing measurements of length, along the direction of motion. This is a coordinate effect which has nothing to do with "warping space" or "contracting space". The spacetime interval, determined by the Minkowski metric is invariant.

 

SR is definitely a "special case". It can be viewed as either the case of general relativity in the absence of gravity or as a localization of general relativity (i.e. general relativity on the tangent space).

[Ras72]

Uniform motion between inertisl reference frames in SR results in differing measurements of length, along the direction of motion. This is a coordinate effect which has nothing to do with "warping space" or "contracting space". The spacetime interval, determined by the Minkowski metric is invariant.

 

SR is definitely a "special case". It can be viewed as either the case of general relativity in the absence of gravity or as a localization of general relativity (i.e. general relativity on the tangent space).

I see. So the orthox interpretation is that it is purely a geometric description to fit the observed invariance of the speed of light. what about in GR? Does GR make make predictions about space being warped under acceleration?And are inertial acceleration and gravity considered entirely equivalent in this respect?

 

 

 

[DrRocket]

I see. So the orthox interpretation is that it is purely a geometric description to fit the observed invariance of the speed of light. what about in GR? Does GR make make predictions about space being warped under acceleration?And are inertial acceleration and gravity considered entirely equivalent in this respect?

 

 

 

 

Curvature, not "warpage" is a property of the spacetime manifold, and it is invariant in general relativity. Curvature of spacetime has nothing whatever to do with acceleration. Curvature is determined by the stress-energy tensor. In GR there is no such thing as "gravity" other than an effect of spacetime curvature. Curvature results in geodesics diverging, which is what results in "tidal forces" and gravitation. There is no such thing as "inertial acceleration" and insofar as one might try to make sense of such a term it is an oxymoron.

 

There is an "equivalence principle" that guided Einstein philosophically under which gravitation and acceleration are taken as indistinguishable, but it has little import in modern geometric formulations of the theory.

 

So, no you don't see, and "orthodox interpretation" has nothing to do with it.

 

For a nice geometric treatment of GR see Gravitation by Misner Thorne and Wheeler. To see SR treated geometrically see The Geometry of Minkowski Spacetime: An Introduction to the Mathematics of Special Relativity by Naber.

[Ras72]

Curvature, not "warpage" is a property of the spacetime manifold, and it is invariant in general relativity. Curvature of spacetime has nothing whatever to do with acceleration. Curvature is determined by the stress-energy tensor. In GR there is no such thing as "gravity" other than an effect of spacetime curvature. Curvature results in geodesics diverging, which is what results in "tidal forces" and gravitation. There is no such thing as "inertial acceleration" and insofar as one might try to make sense of such a term it is an oxymoron.

 

There is an "equivalence principle" that guided Einstein philosophically under which gravitation and acceleration are taken as indistinguishable, but it has little import in modern geometric formulations of the theory.

 

So, no you don't see, and "orthodox interpretation" has nothing to do with it.

 

For a nice geometric treatment of GR see Gravitation by Misner Thorne and Wheeler. To see SR treated geometrically see The Geometry of Minkowski Spacetime: An Introduction to the Mathematics of Special Relativity by Naber.

I understand and thank you for the books advice. As you may have guessed am just starting with the subject and wanted to get a feel before. May ask you how long you have been studying it At what level?

 

[DrRocket]

I understand and thank you for the books advice. As you may have guessed am just starting with the subject and wanted to get a feel before. May ask you how long you have been studying it At what level?

 

 

I have been studying all my life at the highest level that i can handle.