The link above doesn't work, apparently. This is what Grok calls a share link:
Are you sure? As the ship nears the speed of light in the earth frame, surely its acceleration as measured on Earth must decrease.So after a few years of ship time, the acceleration seen on earth is vastly larger than 1 g.
Haven’t read the thread in detail, but I’d like to comment on this particular point.I am only vaguely familiar with Noether's theorem, being an engineer, but everything that is true about conservation of energy assuming Einstein relativity is true about (\gamma m c)*c in both Einstein and Osiak relativity, so basically conservation of temporal component of four-momentum can lead to all the same conserved currents.
Are you sure? As the ship nears the speed of light in the earth frame, surely its acceleration as measured on must decrease.
Haven’t read the thread in detail, but I’d like to comment on this particular point.
In my mind this isn’t so much a matter of conservation, but rather of definition - the very definition of what the term “energy” actually physically means comes from Noether’s theorem. And the answer here is clear - a particular continuous symmetry, being spacetime translation symmetry - leads to a particular and unique conserved quantity, the energy-momentum tensor (NB. not just energy!). And that’s it. In cases where there is no such symmetry, this quantity is not meaningfully defined. Everything else - the momentum 4-vector in SR, the above quoted energy-momentum relations etc - ultimately come from this tensor. But this tensor isn’t an arbitrary choice, it arises uniquely from Noether, so I don’t see how this alternative Osiak version can possibly be compatible with Noether, as it would need to arise from an energy-momentum tensor that has a different form. It’s essentially a quantity that has a different physical meaning.
The momentum 4-vector has a very precise definition - it is the total flux integral of momentum through a space-like hypersurface, and as such comes directly from the energy-momentum tensor, which in turn comes directly from Noether:Osiak relativity says it's incorrect to interpret the four-momentum vector as the energy-momentum four-vector.
The momentum 4-vector has a very precise definition - it is the total flux integral of momentum through a space-like hypersurface, and as such comes directly from the energy-momentum tensor, which in turn comes directly from Noether:
$$P^{\mu}=\int_{\Sigma} \Sigma_{\nu} T^{\nu \mu}$$
This isn’t a matter of interpretation, it’s the unique quantity associated with spatial translation invariance. You can choose to work with a different quantity, but then that quantity necessarily is not going to have the same physical meaning. That was my point. So it’s fine to work with Osiaks expression, but one needs to remember that difference in physical meaning.
Isn't there a mountain of experimental evidence that mass-energy is conserved over time? What test do you propose, Dave Lush , to counter all that? In plain English, if you can.
But that was precisely my point - only in Einstein relativity is the definition actually compatible with Noether’s Theorem, because it emerges directly from the energy-momentum tensor. Osiak essentially defines a different quantity with a different physical meaning - it does not and cannot come from Noether.However, only in Einstein relativity can it be identified as an energy-momentum four vector
Just to add to what I posted above - in Einstein relativity, the definition of “energy” is independent of, and more fundamental then, forces and kinematics. Even before relativity, we already knew that the conserved charge for time-translation invariance isIn Osiak relativity the energy definition is derived from the covariant Minkowski equation of motion F = m A, while in Einstein relativity it's required to define force as change in relativistic three-momentum.
As far as I understand, Osiak rejects Planck's equations of motion, the equivalence principle and ignores the theorem Noether and that relativistic energy is not conserved in particle collisions and $$E_0=\frac{m_0c^2}{2}$$But then in reality nuclear reactors would produce half as much energy and the annihilation energy of a positron and an electron will not correspond to the rest mass energy of the electron for each gamma quantum.
Yes.Osiak relativity has a different energy expression though that doesn't doesn't equate with temporal momentum and so can't be part of the four-momentum, and isn't conserved.
The standard formalism of GR uses a (1,1) representation of the Lorentz group, being symmetric tensors - so of course you are going to be off by a factor of 2 when trying to couple the equations of motion to a particle that has intrinsic half-integer spin. This problem arises not from a failure of the theory, but from an inappropriate choice of formalism. To avoid this issue, all you need to do is pick a different representation of the Lorentz group, such as (½,½), being covariant bispinors, and formulate the same theory of GR in terms of those objects (bispinor tetrad formalism). When you do this, the issue is simply not there anymore.I view it as simply resolving the spin-orbit coupling anomaly without the Thomas precession, which is a weak explanation for that factor of a half.
Just to add to what I posted above - in Einstein relativity, the definition of “energy” is independent of, and more fundamental then, forces and kinematics. Even before relativity, we already knew that the conserved charge for time-translation invariance is
$$Q=\int d^{3}xT^{00}$$
And independently, we know from Hamiltonian mechanics that
$$H=\int d^{3}x\mathcal{H}$$
Therefore, the 00-component of T necessarily has the physical meaning of energy, and thus the same must be true for the 0-component of P. So this isn’t just an arbitrary interpretation, it’s pretty much non-negotiable. Thus is why Osiak’s version cannot have the same physical meaning of “energy”. This is also more fundamental than any kinematics.