How much is Special Relativity a needed foundation of General Relativity

[Aether]

but this freedom no longer exists if there is a locally preferred definition of simultaneity.

Why not? The ability to talk about absolute simultaneity does not force you to abandon the notion of relative simultaneity.

What we seek are the ultimate physical laws that we can validly extrapolate across all space and time. The laws of physics currently assume that the fine-structure constant will be measured to have the same value regardless of time, location, or relative velocity. If the fine-structure constant is confirmed to vary in time (it has already been found to vary in time), then new laws of physics will replace the old laws of physics in order to account for its variation in time. If convenient we may still choose to use the old laws of physics in some circumstances just as we often choose to use Newton's laws today, but we can't validly extrapolate these old laws to extreme conditions because they are known to diverge from reality under extreme conditions.

c is the isotropic round-trip speed of light in ... SR

Only in certain frames.

No, this is a coordinate-system independent parameter. The SI base units of time and length are somewhat arbitrary, and these base units themselves may vary over time as a function of the fine-structure constant, but the round-trip speed of light will otherwise be measured to have the same isotropic value in any inertial frame.

SO(3, 1) is a symmetry group; it doesn't have a time-coordinate. As for Minkowski spacetime (a.k.a. 3+1-dimensional spacetime), all the light-cones tell you is that (for an orthonormal basis) the time axis must lie inside the cones...Again, SO(2, 2) doesn't have a time-coordinate. You mean 2+2 spacetime.

Ok.

It is locally preferred in the sense that all observers can agree on this definition of simultaneity, and actually realize it within a laboratory, using only local physical properties

That's not very special. For example, any bit of matter in the universe allows you to give a local definition of simultaneity, and all observers will agree upon that definition.

Lorentz covariance (e.g., the basic principle that the laws of physics are invariant under a shift of inertial reference frames) is not valid unless \alpha itself is invariant under any shift of inertial reference frames. For example, consider the fine-structure of hydrogen (e.g., Dirac's equation) as an example of an objective law of physics. This law explains the various discrete emission frequencies (or "lines") that are observed in ionized hydrogen plasmas, and one of the ways that it is often used is cosmology is to measure the recession velocities of stars, galaxies, quasars, etc.. The relativistic Doppler-shift is used to describe how any such line frequency transforms between two inertial frames, but this assumes that the line frequency of the emitter is the same as the line frequency of a laboratory reference at the detector (e.g., that the fine-structure constant does not vary with time or space). If \alpha varies with time, then we can foliate our pseudo-Riemannian manifold into hypersurfaces of constant \alpha, and there will be one and only one (locally preferred) inertial frame in which \alpha is invariant under spatial translations.

No. The hypothesis of 4+0 space fails because there is an observable geometric difference between "forward in time" and, say, "North".

How is that observed using a Michelson interferometer?

(the symmetry group of pre-relativistic mechanics is not SO(4, 0))

Ok.

When I say that, I mean experiments that (attempt to) involve only geometric things, like lengths and angles. In particular, they do not involve non-geometric things like the observed matter distribution, CMB temperature, or the local values of (non-geometric) constants like alpha.

Which experiment to probe space-time geometry does not involve particles like electrons and photons? Such experiments can only probe the geometry of spatially extended particles, but not space and time per se:

Physical objects are not in space, but these objects are spatially extended. In this way the concept 'empty space' loses its meaning. The field thus becomes an irreducible element of physical description, irreducible in the same sense as the concept of matter (particles) in the theory of Newton." (Albert Einstein, 1954)

 

[Hurkyl]

Lorentz covariance (e.g., the basic principle that the laws of physics are invariant under a shift of inertial reference frames) is not valid unless alpha itself is invariant under any shift of inertial reference frames.

Have you considered that alpha may be a scalar field?

If alpha varies with time, then we can foliate our pseudo-Riemannian manifold into hypersurfaces of constant alpha, and there will be one and only one (locally preferred) inertial frame in which alpha is invariant under spatial translations.

Any locally nonconstant scalar field let's you do that. It may be convenient. I don't see why one would consider it preferred.

Incidentally... those who think alpha is varying, do they think it to be a strictly increasing function of time? Or is it permitted to vary back and forth?

How is that observed using a Michelson interferometer?

I have no idea. Why does it matter?

Which experiment to probe space-time geometry does not involve particles like electrons and photons?

When I say "does not involve", I meant the thing we're attempting to measure, not the apparatus doing the measuring.

 

[Aether]

Have you considered that alpha may be a scalar field?

No.

Any locally nonconstant scalar field let's you do that. It may be convenient. I don't see why one would consider it preferred.

\alpha is the most fundamental of the physical "constants". Most of the other dimensionful constants, including c are subject to varying in time if \alpha varies in time.

You haven't responded to this: "If you don't agree that this would falsify CS, then please give an example of a real experiment that could falsify it." You seem to be arguing that CS, Lorentz covariance, and special relativity aren't falsifiable.

Incidentally... those who think alpha is varying, do they think it to be a strictly increasing function of time? Or is it permitted to vary back and forth?

I think that most people would presume that if alpha is varying, then it is varying with the expansion of the universe. Although this expansion may one day reverse into a contraction, nobody thinks that this has happened yet since the big bang.

I have no idea. Why does it matter?

The criteria used to validate Minkowski space-time (e.g., which includes the results of the Michelson-Morley experiment) over Euclidean space and time should be the same criteria that we continue to use for falsifying Minkowski space-time in view of some other principle like the holographic principle for example. If you make an argument that Minkowski space-time can't be falsified by a certain experiment, then I will deny you the benefit of similar experiments to falsify Euclidean space and time.

When I say "does not involve", I meant the thing we're attempting to measure, not the apparatus doing the measuring.

But what is it that you think we are attempting to measure there? Empty space and time per se aren't physical at all, it is only the geometry of particle fields that we are concerned with:

Physical objects are not in space, but these objects are spatially extended. In this way the concept 'empty space' loses its meaning. The field thus becomes an irreducible element of physical description, irreducible in the same sense as the concept of matter (particles) in the theory of Newton." (Albert Einstein, 1954)

 

[Hurkyl]

the round-trip speed of light will otherwise be measured to have the same isotropic value in any inertial frame.

(emphasis mine) In other words, only in certain frames.

You seem to be arguing that CS, Lorentz covariance, and special relativity aren't falsifiable.

You're going to have to state precisely what you mean by CS. But you cannot falsify a convention, by virtue of the fact it's a definition and not a theory.


Lorentz covariance says that the laws of physics remain unchanged under a Lorentz transformation. It does not say that the values of all quantities remain unchanged under a Lorentz transformation. Lorentz covariance doesn't require that alpha = 1/137.03... in all frames; it merely requires that

alpha = e^2 / (hbar * c * 4 * pi * epsilon_0)

in all inertial frames. (Assuming that is, in fact, the correct relation in general)

 

[Hurkyl]

The criteria used to validate Minkowski space-time (e.g., which includes the results of the Michelson-Morley experiment) over Euclidean space and time should be the same criteria that we continue to use for falsifying Minkowski space-time in view of some other principle like the holographic principle for example

The Michelson inferometer mattered for Newton vs SR because they were known to disagree about the results. The MM experiment certainly cannot be used to falsify SR, because SR is consistent with the result. An inferometer is only useful for deciding between SR and something else if SR and something else are known to disagree about what the inferometer says.


Incidentally, as far as general relativity is concerned, the Lorentz group isn't very special. The laws of physics are to remain unchanged under ANY diffeomorphism. That includes anything in the Lorentz group, the Gallilean group, SO(4, 0), SO(2, 2), and any other group of diffeomorphisms you can imagine. The only thing special about the Lorentz group is that, in addition to preserving the laws of physics, it additionally locally preserves lengths and angles for a metric with signature -+++.

 

[Aether]

...the instantaneous value of a second time-coordinate might represent an extremely large tangential velocity (4*pi*R*mc^2/hbar) for this object. Integrate these two velocities over absolute time to get instantaneous positions. Yes, the holographic principle does imply that there is some wildness going on under the hood of our manifold...If it turns out that alpha does not vary in time, then the principle of the conventionality of simultaneity (CS) is safe. However, if it does turn out to vary in time then CS is falsified.

coalquay404 recently referenced http://arxiv.org/abs/gr-qc/0612118" wherein the authors state:

By studying the 5D geodesic equations we are able to reproduce the usual electrodynamics for a test-particle in a 4D space-time, where the charge-mass ratio is ruled out as follows q/m=u_5(1+\frac{u_5^2}{\phi^2})^{-1}. In this formula u_5 is the fifth covariant component of the 5D velocity and can be proved that it is a constant of motion and a scalar under KK transformations...A large scalar field (\phi>10^{21} for the electron) allow us to have realistic value for the charge mass ratio avoiding the problem of Planckian mass, and, moreover, allow us to restore the conservation of charge at a satisfactory degree of approximation. Actually, a time-varying charge is very interesting; an isotopic, slow varying \phi can explain the time-variation of the fine structure constant over cosmological scale which seems to be inferred by recent analysis.

I can't do calculations in Kaluza-Klein (KK) theory yet, but comparing what these authors say here (implying that u_5>5.7\times 10^{30} m/s) to the "extremely large tangential velocity" component that I referred to above for an electron of approximately 5.1\times 10^{47} m/s (I chose R=5.24\times 10^{25} meters here to get the even c^2 factor below) we can see that they differ by a factor of about c^2...maybe they are related (or the same). KK theory adds a dimension to unify gravity with electrodynamics, but the holographic principle subtracts a dimension leaving a net four dimensions when combined.

You're going to have to state precisely what you mean by CS. But you cannot falsify a convention, by virtue of the fact it's a definition and not a theory.

I'm reading The Philosophy of Space & Time by Hans Reichenback, and will come back to this discussion later.

 

[Chris Hillman]

Some comments and caveats

If one had to built an invariant theory for gravitation, applicable in any system of coordinate, could it not be possible to create one without knowing about SR (constancy of c, EM, ...).

From this, it seems you are asking about competitors to gtr which might in some sense not incorporate str. Since str describes the geometry of tangent spaces in Lorentzian manifolds, this would probably require looking at non-metric theories. If so, I find the title puzzling, since gtr is not only a metric theory of gravitation, but a specific such theory.

You mentioned "applicable in any system of coordinates"; in the context of classical gravitation, this is usually interpreted to mean, technically speaking, "diffeomorphism covariance", which gets us back to smooth manifolds. So you probably need to refine what you mean by this in order to consider non-metric theories.

The structure of Newtonian gravity turns out to be more complicated than the structure of general relativity, though it does involve one less parameter (c).

Depends upon what you mean by "complexity", I guess. Interestingly enough, Einstein's notion (sometimes translated as "strength" although a better word would be "richness") attempts to assess the variety of distinct solutions. Then for example Maxwell's theory is actually richer than Newtonian gravitation, as you would expect from the fact that the field equation of Newtonian gravitation (in the classical field theory reformulation) is the same as that of electrostatics, a special case of Maxwell's theory.

Apparently you can also get GR by looking for a field that describes massless spin-2 particles.

On a background Lorentz spacetime.

In the case of weak fields, in linearized gtr you write the metric as a linear perturbation from an unobservable Minkowski background metric, so that mathematically speaking we treat "the gravitational field" as a second rank tensor field in Minkowski spacetime, which then suggests a naive quantization. Deser et al. showed that you can systematically introduce higher and higher order corrections, each time obtaining a field theory which is not self-consistent. But in the limit you obtain something self-consistent which is locally equivalent to gtr. However, this is not a true quantum theory of gravitation.

 

[Chris Hillman]

The groups O(4), O(1,3), O(2,2)

Hi, Aether wrote:

His second choice has Poincaré symmetry, and only takes on Lorentz symmetry if we arbitrarily assume that the one-way speed of light is generally isotropic; this is a convention, and isn't required. I'm not sure about the other two yet.

The isometry groups of three types of "pseudo-Euclidean" four-manifolds mentioned by Hurkyl, respectively E^4, \; E^{1,3}, \; E^{2,2} are semidirect products of the translation group {\bold R}^4 with the isotropy groups O(4), \; O(1,3), \, O(2,2).

Let's step back and look at a more familiar example. The isotropy group O(3) is the rotation group of E^3, and the semidirect product of this with the translation group {\bold R}^3 gives the euclidean group E(3) = {\bold R}^3 | \! \! \times O(3).

Similarly, the isotropy group O(1,3) is the full Lorentz group (the proper orthochronous Lorentz group is an index four subgroup of this), and the isometry group E(1,3) = {\bold R}^4 | \! \! \times O(1,3) is the Poincare group.

In each case, the translation group is a normal subgroup, and there is one conjugate of the isotropy group associated with each point in the geometry, corresponding to the freedom to "rotate" about each point.

See for example Jacobson, Basic Algebra I, or Artin, Geometric Algebra.

If I am not mistaken, a (2+2)-spacetime [i.e. signature ++--] admits closed timelike curves.

Yes, in every neighborhood, because E^{2,2} admits them.

One place where this geometry naturally arises is the following: suppose we represent M(2,R) (two by two real matrices) as a four dimensional real algebra, and seek the orbits under conjugation. Since conjugation leaves the trace invariant, this suggests rewriting our matrices in new variables on of which is the trace. But conjugation also leaves the determinant invariant, and the determinant in fact gives M(2,R) the structure of E^{2,2}.

Going up one more dimension, it seems worthwhile to mention that the point symmetry group of the three-dimensional Laplace equation is SO(1,4), the (proper) conformal group of E^3, plus an infinite dimensional group arising from the linearity of the Laplace equation. The point symmetry group of the two-dimensional wave equation (time plus two space variables) is SO(2,3), the (proper) conformal group of E^{1,2}, plus an infinite dimensional group arising from the linearity of the wave equation. And so on. (The conformal groups of the two dimensonal pseudoeuclidean spaces E^2, \; E^{1,1} are infinite dimensional, by virtue of helpful "algebraico-analytical accidents".)

Hope this helps.

 

[Aether]

If it's an "explanation" for the uncertainty principle, then it should make the same empirical predictions as the uncertainty principle--if you're saying there's an upper limit to the momentum no matter how much you reduce the uncertainty in the position, that would seem to be a violation of the uncertainty principle.

Let me clarify this (from an old thread). If you measure the velocity of an object as as tends to zero, Heisenberg's uncertainty principle gets in the way. The more accurately you measure x (as tends to zero), the less accurately can you measure momentum. In the limit, the momentum tends to infinity (implying a velocity of c).

Some of the concepts that you have referred to above (e.g., to "measure the velocity of an object", "the less accurately can you measure momentum", and "a velocity of c") are coordinate-system dependent. Isn't how one is obliged to interpret Heisenberg's uncertainty principle determined by their choice of coordinate system?That is how I interpreted what Paul Dirac said, but I suspect that interpretations may differ according to one's choice of coordinate system. Do you think that the difference between your interpretation of quantum theory and mine might ultimately be reduced to a difference in our choice of coordinate-systems?

In http://arxiv.org/abs/gr-qc/0309134" paper P.S. Wesson describes "Five-Dimensional Relativity and Two Times":

It is possible that null paths in 5D appear as the timelike paths of massive particles in 4D, where there is an oscillation in the fifth dimension around the hypersurface we call spacetime...a cou-
ple of exact solutions of the field equations of 5D relativity have recently
been found which have good physical properties but involve manifolds with
signature [+(− − −)+] that describe two “time” dimensions.

What I'm suggesting is that, in view of the holographic principle, a manifold like this might be equivalent to some other manifold having a signature of [+--+].

See for example Jacobson, Basic Algebra I, or Artin, Geometric Algebra.

Thanks. I am working on getting those books.

 

[Hurkyl]

What I'm suggesting is that, in view of the holographic principle, a manifold like this might be equivalent to some other manifold having a signature of [+--+].

In what sense would they be "equivalent"?!

Here's a quick insanity check:
If a 5-dimensional manifold is "equivalent" to a 4-dimensional manifold via the holographic principle,
and if a 4-dimensional manifold is "equivalent" to a 3-dimensional manifold via the holographic principle,
and if a 3-dimensional manifold is "equivalent" to a 2-dimensional manifold via the holographic principle,
and if a 2-dimensional manifold is "equivalent" to a 1-dimensional manifold via the holographic principle,
and if a 1-dimensional manifold is "equivalent" to a 0-dimensional manifold via the holographic principle,

then why would we ever study anything but 0-dimensional manifolds? They very easy things to understand!

 

[Aether]

In what sense would they be "equivalent"?!

In the same sense as J.D. Bekenstein intends here:

An astonishing theory called the holographic principle holds that the universe is like a hologram: just as a trick of light allows a fully three dimensional image to be recorded on a flat piece of film, our seemingly three-dimensional universe could be completely equivalent to alternative quantum fields and physical laws "painted" on a distant, vast surface.The physics of black holes--immensely dense concentrations of mass--provides a hint that the principle might be true. -- J.D. Beckenstein, Information in the Holographic Universe, Scientific American:p59, (August 2003).

Here's a quick insanity check:
If a 5-dimensional manifold is "equivalent" to a 4-dimensional manifold via the holographic principle,
and if a 4-dimensional manifold is "equivalent" to a 3-dimensional manifold via the holographic principle,
and if a 3-dimensional manifold is "equivalent" to a 2-dimensional manifold via the holographic principle,
and if a 2-dimensional manifold is "equivalent" to a 1-dimensional manifold via the holographic principle,
and if a 1-dimensional manifold is "equivalent" to a 0-dimensional manifold via the holographic principle,

then why would we ever study anything but 0-dimensional manifolds? They very easy things to understand!

According to P.S. Wesson the [+(---)+] signature manifold has "good physical properties", and according to J.D. Bekenstein "our seemingly three-dimensional universe could be completely equivalent to alternative quantum fields and physical laws "painted" on a distant, vast surface" so that the (---) part of the [+(---)+] signature manifold might be completely equivalent to the (--) part of a [+(--)+] signature manifold. I am assuming that a [+(--)+] signature manifold having the same "good physical properties" as the [+(---)+] would be something worth studying; what do you think?

 

[lalbatros]

(multiple quotation) ... holographic principle ...

The holographic principle indeed questions the notion of space and dimensions.

I think that the origin of the holographic principles lies in the point of view that physics is about information and that the universe can hold a large but a finite amount of information that are "processed" at a finite rate. (see http://www.phy.duke.edu/~hsg/einstein/seth-lloyd-ultimate-computer.pdf")

Therefore, I think the holographic principle does not suggest us simply to drop one dimension in physics and makes thinks a bit simpler. Actually, it illustrates -for me- the possibility that dimensions themselves might be the simplification while the reality might very well be space and dimension-free.

The ultimate physical description of the universe might very well be a huge amount of qbits and the existence of space and the 4 dimensions might only be a very happy opportunity to make physics simpler.

I am very curious to see if such a "reverse" point of view, from qomputers to the universe, could bring us something useful.

Michel

 

[Aether]

Thanks for the interesting article Michel.

...black holes could in principle be 'programmed': one forms a black hole whose initial conditions encode the information to be processed, let's that information be processed by the Planckian dynamics at the hole's horizon, and extracts the answer of the computation...

At the black-hole limit, computation is fully serial: the time it takes to flip a bit and the time it takes a signal to communicate around the horizon of the hole are the same.

Therefore, I think the holographic principle does not suggest us simply to drop one dimension in physics and makes thinks a bit simpler.

I'm not looking "simply to drop one dimension in physics and make things a bit simpler", but rather to unify physics in terms of "planckian dynamics at the hole's horizon" (or rather at the universe's horizon); either that, or to rule out the possibility of such a thing. The holographic principle doesn't help do that, but rather it may help explain how such a model might appear to us as a projection in four-dimensional space-time.

 

[Sammy k-space]

Special Relativity is just Linear Doppler effect: C is constant by definition; the mass/energy of the photon is conserved for a stationary observer relative to the source, but for a source moving away from the observer there is a decrease in frequency as
v^2/2C^2 ie. vv/2CC where v is the velocity of the source away from the observer. It is a vector quanity; the quantity is added for a source moving toward the observer. This is easily calculated as E=mCC=hn; CC=E/m ie. C squared is the constant of proportionaliy between a mass and it's energy.
For general relativity we can look at two cases: first let a photon move toward the center of mass of an observer, since C is constant the gravitational increase is seen as an increase in frequency; for the other case let the photon be traveling close to a mass but toward an observer stationary to the source; the photon will curve toward the mass, but since C is defined as constant the velocity along the curve is C but the observer will see the curve and the shift in frequency. The change will be as if m=hn/CC.
For a very special case take twin photons with the same frequency and moving in the opposite direction, the observer is stationary relative to the source and "sees" one photon coming and one leaving, but the photons overlap in the view, so E1=hn and E2=hn but sum of the vectors is zero.

 

[jimmy neutron]

I'm not sure what you're trying to say. I meant that SR is just a special case of general relativity, so everything in SR is contained in GR.

Within both special and general relativity, there is an unavoidable constant we call c. Of course it isn't necessary that that parameter has anything to do with electromagnetic phenomena, but experimentally, it does.

By that I assume that you mean that, otherwise, light signals would have to travel at speeds less than c?

 

[Deepak Kapur]

If one had to built an invariant theory for gravitation, applicable in any system of coordinate, could it not be possible to create one without knowing about SR (constancy of c, EM, ...).

Could such an off-road journey teach us something, and couldn't SR pop up in some other way?

Thanks for your ideas,

Michel

I doubt the predictions of relativity. To take a simple example, 'Time Slows With Increasing Speed'. If time slows down, so will all the processes like the functioning of our hearts, brains, the solar system, the atomic system and so on. So, the universe will just tend to come to a stand still at extremely high speeds. This is absurd!

 

[Fredrik]

I doubt the predictions of relativity. To take a simple example, 'Time Slows With Increasing Speed'. If time slows down, so will all the processes like the functioning of our hearts, brains, the solar system, the atomic system and so on. So, the universe will just tend to come to a stand still at extremely high speeds. This is absurd!

The post you're quoting was written in 2006.

Do you really think that you can refute the most well-understood and most thoroughly tested theory in the history of science with an argument that any kid can come up with, and without making an effort to find out what the theory says?

 

[Deepak Kapur]

The post you're quoting was written in 2006.

Do you really think that you can refute the most well-understood and most thoroughly tested theory in the history of science with an argument that any kid can come up with, and without making an effort to find out what the theory says?

Yes, you are right. It's a childish question. But don't underestimate the importance of such questions as they often turn out to be the germs of excellent theories in case of gifted individuals like Einstein ( he himself was used to such questions).

A few more childish questions.

1. Can we ever understand the mystery of nature. Suppose the String Theory (which in some cases even refutes Einstein's Theories) is able to find the fundamental particle. The immediate question would be 'What is this 'fundamental' composed of?

2. The only saving grace is the adage 'Something is Better than Nothing'. Even scientists are aware of this and never give up their scientific enquiries even if faced with bizarre contradictions like wave-particle duality and all the other paradoxes. Mind you, many scientist dealling with quantum mechanics are still skeptical of it, but they don't want to undermine the superstructure of science and have learned to live with it. Different kinds of politics is also involved in such an attitude. After all only a child can have the audacity to ask God 'Who made you?'

3. How can uniform motion be ever possible, when galaxies are moving away from each other at incredible speeds and time is continuously slowing down. Doesn't science feel it 'convenient' to deal with appoximations and simplifications rather than reality (whatever that is).

4.You would agree that in the laws of mechanics no mention is made of the shape of the body undergoing motion, whereas in real life it makes hell of a difference. Similarly it's extremely difficult to solve three-body problem (what to talk of greater number of bodies), because of the feedback effect. But scientists always tend to avoid such feedbacks and proceed with the simplest of cases. Can it lead us further or enmesh us in a labyrinth of mathematics and incomplete laws? (O! Lord, at least give us a single universal law that is proof against any kind of further enquiry!)

More will follow in case you reply.

 

[Mentz114]

I doubt the predictions of relativity. To take a simple example, 'Time Slows With Increasing Speed'. If time slows down, so will all the processes like the functioning of our hearts, brains, the solar system, the atomic system and so on. So, the universe will just tend to come to a stand still at extremely high speeds. This is absurd!

'Time slows with increasing speed' is not what relativity says - so your argument is based on a complete misunderstanding of relativity. Also, you have no idea what science is about and for.

 

[jtbell]

I doubt the predictions of relativity.

Check out the experimental evidence:

Experimental Basis of Special Relativity

 

[Deepak Kapur]

'Time slows with increasing speed' is not what relativity says - so your argument is based on a complete misunderstanding of relativity. Also, you have no idea what science is about and for.

Plz don't be impatient. Impatience may also signal absence of logic.

There are many interpretations of relativity ( some even contradictory).

To go by your interpretation a very-2 high gravitational field would in theory make a clock stop functioning (or make it extremely-2 slow) for another observer who is far away from the gravity source.

This again amounts to what I have said above. Processes can't come to a stand still just by the presence of super high gravity.

 

[Deepak Kapur]

Check out the experimental evidence:

Experimental Basis of Special Relativity

Thanks. I have already read that.

 

[Mentz114]

Nothing you've said is worth refuting because you don't understand what you are talking about.

For instance

Processes can't come to a stand still just by the presence of super high gravity.

That is not what GR predicts. Again you base your remarks on misunderstandings.

 

[Fredrik]

More will follow in case you reply.

I have answered questions like these many times in the past, but I think I'll pass this time. I don't want to spend 10-15 hours explaining physics (starting with an explanation of what a theory is) to someone who probably would ignore everything I say anyway. This is a forum for people who want to learn stuff, not for people who want to criticize things they don't understand.

Plz don't be impatient. Impatience may also signal absence of logic.

And criticizing the best understood and most thoroughly tested theory in the history of science without making an effort to understand what it says, signifies what exactly? You can't demand that others be patient with you when you show up here with this attitude.

To go by your interpretation a very-2 high gravitational field would in theory make a clock stop functioning (or make it extremely-2 slow) for another observer who is far away from the gravity source.

This again amounts to what I have said above. Processes can't come to a stand still just by the presence of super high gravity.

The problem with your posting this "argument" against relativity (twice!?) isn't that it's extremely naive. It's perfectly OK to ask uneducated questions. The problem is that you clearly know that your argument can't be right, and still talk to us as if you have disproved relativity. If it had been possible to disprove relativity with an argument that any kid can come up with, it would have been done a hundred years ago, and we wouldn't need your help with it. If you continue with this nonsense, you might get banned from the forum.

 

[Deepak Kapur]

I have answered questions like these many times in the past, but I think I'll pass this time. I don't want to spend 10-15 hours explaining physics (starting with an explanation of what a theory is) to someone who probably would ignore everything I say anyway. This is a forum for people who want to learn stuff, not for people who want to criticize things they don't understand.


And criticizing the best understood and most thoroughly tested theory in the history of science without making an effort to understand what it says, signifies what exactly? You can't demand that others be patient with you when you show up here with this attitude.


The problem with your posting this "argument" against relativity (twice!?) isn't that it's extremely naive. It's perfectly OK to ask uneducated questions. The problem is that you clearly know that your argument can't be right, and still talk to us as if you have disproved relativity. If it had been possible to disprove relativity with an argument that any kid can come up with, it would have been done a hundred years ago, and we wouldn't need your help with it. If you continue with this nonsense, you might get banned from the forum.

I am not trying to refute anything but am trying to satisy my curiosity. As far as this forum goes, I haven't got any logical answer till now apart from accusations and non-sensical arguments.

It's a usual strategy of such forums.

1. Goad someone so that he indulges in impatient remarks.

2. If someone is not provoked, dismiss him as being non-sensical.

Plz refrain from 'blind faith' in anything and try to give logical answers to the points (however uneducated they might be) I have raised.

 

[Fredrik]

I am not trying to refute anything but am trying to satisy my curiosity.

I might have believed you if you had said something to show us that you understand that these are the only possible reasons why your understanding of relativity disagrees with your intuition about the real world:

1. You don't actually understand what these theories (SR and GR) say.

2. Your intuition is wrong.

Instead you have been strongly suggesting that the problem is with relativity. That attitude is very inappropriate in this forum.

It's a usual strategy of such forums.

1. Goad someone so that he indulges in impatient remarks.

2. If someone is not provoked, dismiss him as being non-sensical.

Plz refrain from 'blind faith' in anything...

That's definitely not true, but it's a usual strategy of science-haters to make accusations like this one, where they describe their own behavior and claim it's how skeptics and scientists behave. This is also inappropriate here.

...and try to give logical answers to the points (however uneducated they might be) I have raised.

You haven't raised any points. You haven't asked any questions. All you've done is to suggest that your "argument" means that relativity is wrong. (This is also an implicit suggestion that every scientist in the last 100 years was a complete idiot).

 

[atyy]

I doubt the predictions of relativity. To take a simple example, 'Time Slows With Increasing Speed'. If time slows down, so will all the processes like the functioning of our hearts, brains, the solar system, the atomic system and so on. So, the universe will just tend to come to a stand still at extremely high speeds. This is absurd!

Yes, it is absurd. The statements you make are pieced together from popular explanations of relativity. In relativity there are several times - proper time and coordinate time, and there are many coordinate times. If you take a statement about proper time and another statement about coordinate time and draw logical conclusions from them, you will be all mixed up.

So things to distinguish: proper time vs coordinate time, inertial frame versus noninertial frame, local reference frame versus global reference frames, special relativistic time dilation vs general relativistic time dilation. Only predictions about experiments really matter.

 

[Deepak Kapur]

I might have believed you if you had said something to show us that you understand that these are the only possible reasons why your understanding of relativity disagrees with your intuition about the real world:

1. You don't actually understand what these theories (SR and GR) say.

2. Your intuition is wrong.

Instead you have been strongly suggesting that the problem is with relativity. That attitude is very inappropriate in this forum.


That's definitely not true, but it's a usual strategy of science-haters to make accusations like this one, where they describe their own behavior and claim it's how skeptics and scientists behave. This is also inappropriate here.


You haven't raised any points. You haven't asked any questions. All you've done is to suggest that your "argument" means that relativity is wrong. (This is also an implicit suggestion that every scientist in the last 100 years was a complete idiot).

I didn't think 'political correctness' is also required in 'public forums'.

Anyhow, answer my next question (except saying that the question itself is wrong).

When there is no absolute concept of time and distance (as stated by general relativity), how can we talk about an absolute entity like the Speed of light?

 

[Fredrik]

Now that's a real question.

There's just one little problem. The complete answer is long and mathematical. It would take a long time to write it down, and I don't even know if you'd be interested in a mathematical answer. The very short answer is that the speed of light isn't absolute. You can make it whatever you want by choosing an appropriate coordinate system. But there's a class of coordinate systems that are particularly important. They're called inertial frames. The claim that the speed of light is "invariant" actually means that it's the same in all inertial frames, not that it's the same in all coordinate systems.

Why is it the same in all inertial frames? That's just a mathematical property of inertial frames on Minkowski spacetime and null geodesics, the curves that we use to represent the motion of massless particles mathematically.

Why do we use this particular model of space and time? Because the theory based on it makes better predictions about results of experiments than theories based on other models. There is actually only one other model that's consistent with the requirement that inertial observers would describe each other as moving as described by straight lines, and that's the Galilean spacetime, which is used in Newtonian mechanics.

 

[Deepak Kapur]

Now that's a real question.

There's just one little problem. The complete answer is long and mathematical. It would take a long time to write it down, and I don't even know if you'd be interested in a mathematical answer. The very short answer is that the speed of light isn't absolute. You can make it whatever you want by choosing an appropriate coordinate system. But there's a class of coordinate systems that are particularly important. They're called inertial frames. The claim that the speed of light is "invariant" actually means that it's the same in all inertial frames, not that it's the same in all coordinate systems.

Why is it the same in all inertial frames? That's just a mathematical property of inertial frames on Minkowski spacetime and null geodesics, the curves that we use to represent the motion of massless particles mathematically.

Why do we use this particular model of space and time? Because the theory based on it makes better predictions about results of experiments than theories based on other models. There is actually only one other model that's consistent with the requirement that inertial observers would describe each other as moving as described by straight lines, and that's the Galilean spacetime, which is used in Newtonian mechanics.

Why is it same in all the inertial frames when there is no absolute definition of time and distance (time dialtion, length contraction) even in the inertial frames. As a matter of fact how can (or should) speed be determined with so much of relativity around (even in inertial frames of reference).