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Physicists Detect Gravitational Waves, Proving Einstein Right

nytimes.com

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Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#491

Post by raattgift »

egwor wrote: post #323
kordless wrote: post #306

Earlier quoted context omitted.

I'm going with the theory that black holes ARE gravitons themselves.

There always seem to be pairs (as in yin and yang), so could something like anti-gravitons exist too?

Sure, and in several theories of gravitation where there are gravitons as an uncharged massless spin-2 gauge boson (General Relativity isn't one of these; it doesn't have any gravitons at all, although the non-quantized classical gravitational waves have spin-2 symmetry) then gravitons are their own anti-particles, just as photons (uncharged massless spin-1 gauge bosons) are their own anti-particles in the Standard Model.

(i.e., anti-gravitons and gravitons are the same thing, just as anti-photons and photons are the same thing).

There are a variety of other theories of gravitation with gravitons, but as far as I know, there are none in which gravitons are not their own antiparticles. (There may be such theories available in universes with a very different cosmological constant or with different numbers of dimensions than the one we are in).

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#493

Post by effie »

pdonis wrote: post #484
effie wrote: post #483

Earlier quoted context omitted.

As I wrote above, I agree with you on the requirements for replacement theory. My point is that a new theory of a phenomenon does not need to replace and reproduce all the results of the old theory to be considered worthwile, competing, acceptable.

Can you give an example of a new theory that was considered worthwhile even though it didn't replace and reproduce all the results of the old theory? I'm not aware of any. (The Copernicus example given upthread is not a valid example, as I said in response to that post.)

Schroedinger's theory of hydrogen atom and his wave mechanics (1926). It explained positions of emission lines of excited hydrogen, but it didn't explain how the atoms lose excitation energy as there is no c and no spontaneous emission in that theory. Larmor's older theory (1897) explained how the energy is lost - by EM radiation - and gave formula connecting acceleration and losses that is used to this day.

Joseph Larmor, LXIII, On the theory of the Magnetic Influence on Spectra ; and on the Radiation from moving Ions, Philosophical Magazine Series 5 Vol. 44, Iss. 271, 1897

Erwin Schrodinger, Quantisierung als Eigenwertproblem. Annalen der Phys. 384 (4) (1926)

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#494

Post by pdonis »

effie wrote: post #493
pdonis wrote: post #484

Earlier quoted context omitted.

Can you give an example of a new theory that was considered worthwhile even though it didn't replace and reproduce all the results of the old theory? I'm not aware of any. (The Copernicus example given upthread is not a valid example, as I said in response to that post.)

Schroedinger's theory of hydrogen atom and his wave mechanics (1926). It explained positions of emission lines of excited hydrogen, but it didn't explain how the atoms lose excitation energy as there is no c and no spontaneous emission in that theory. Larmor's older theory (1897) explained how the energy is lost - by EM radiation - and gave formula connecting acceleration and losses that is used to this day. Joseph L…

> Schroedinger's theory of hydrogen atom and his wave mechanics (1926).

This was not a "new theory" that was competing with any "old theories". It was a tentative model in a regime where no previous theory existed, and it was never claimed to cover anything outside that limited regime. It wasn't competing with any other theories, because there were no other theories to compete with. The question of whether or not Schrodinger's model reproduced the predictions of the "old" theory never arose, because there was no "old" theory. (Technically, there was a sort of "old" theory of the hydrogen atom--Bohr's model--but Schrodinger's model did reproduce all of its correct predictions, plus it added more correct predictions of things that the Bohr model got wrong.)

The position with regard to gravitational waves is very different; we already have a comprehensive, fundamental theory--General Relativity--that explains them. Any alternative theory that only explained GWs, and didn't also explain all the other experimental results that GR explains, would be a nonstarter.

> Larmor's older theory (1897)

This wasn't a separate "theory" at all; it was just a derivation of a particular formula using an already known theory, Maxwell's Equations.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#495

Post by effie »

pdonis wrote: post #494
effie wrote: post #493

Earlier quoted context omitted.

Schroedinger's theory of hydrogen atom and his wave mechanics (1926). It explained positions of emission lines of excited hydrogen, but it didn't explain how the atoms lose excitation energy as there is no c and no spontaneous emission in that theory. Larmor's older theory (1897) explained how the energy is lost - by EM radiation - and gave formula connecting acceleration and losses that is used to this day. Joseph L…

> Schroedinger's theory of hydrogen atom and his wave mechanics (1926). This was not a "new theory" that was competing with any "old theories". It was a tentative model in a regime where no previous theory existed, and it was never claimed to cover anything outside that limited regime. It wasn't competing with any other theories, because there were no other theories to compete with. The question of whether or not Sch…

Schroedinger theory certainly was a new theory of the atom and later of molecules at that time, successfully competing and largely replacing classical EM models of atoms and molecules such as Larmor's theory of molecules, although it didn't cover the EM radiation aspect and EM theory needs to be used in parallel with Schroedinger's to get, say, intensities of emission lines. I think this is a good example of what I was saying in the first post. It is the new benefit that the theory brings, not reproduction of every single result of the previous theories, that makes the new theory interesting and helps its adoption. Cases where the new theory completely replaces the old theory and reproduces all of its positive results happen too, but are not the only way how new knowledge is adopted.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#496

Post by cyphar »

Manishearth wrote: post #467
cyphar wrote: post #394

Earlier quoted context omitted.

Only electrons get mass from the Higgs mechanism. Most of your mass comes from your protons and neutrons (or rather the energy "stored" in the bonds between the quarks that make them up).

You're talking about binding energy, and that's not where the majority of mass comes from. All massive particles get their mass from the Higgs field.

This is true for fundamental particles. However, more than 99% of the protons mass doesn't come from its constituent parts. I couldn't find any papers on this question in the 10 minutes I spent googling (and I don't have my QCD textbook handy), but here's a few links:

* http://physics.stackexchange.com/questions/64232/your-mass-i... * https://en.wikipedia.org/wiki/Proton#Quarks_and_the_mass_of_...

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#497

Post by cyphar »

Manishearth wrote: post #476
rotorblade wrote: post #472

Earlier quoted context omitted.

All _fundamental_ particles gets their mass from the Higgs (up to some issues with the neutrinos). Composite particles, say the Proton, is a strongly coupled system (that is, can not be described by perturbation theory) and it does not have the mass being the sum of its constituents (not even most of it). Hence, it is not known what gives most of the mass of particles such as the Proton.

Er, sorry, implicitly was talking about fundamental particles. IIRC we do know where protons get their mass. The internal color field has some energy, thus some mass, which comes from that field interacting with Higgs.

E=mc^2 doesn't come from the Higgs mechanism.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#498

Post by pdonis »

effie wrote: post #495
pdonis wrote: post #494

Earlier quoted context omitted.

> Schroedinger's theory of hydrogen atom and his wave mechanics (1926). This was not a "new theory" that was competing with any "old theories". It was a tentative model in a regime where no previous theory existed, and it was never claimed to cover anything outside that limited regime. It wasn't competing with any other theories, because there were no other theories to compete with. The question of whether or not Sch…

Schroedinger theory certainly was a new theory of the atom and later of molecules at that time, successfully competing and largely replacing classical EM models of atoms and molecules such as Larmor's theory of molecules, although it didn't cover the EM radiation aspect and EM theory needs to be used in parallel with Schroedinger's to get, say, intensities of emission lines. I think this is a good example of what I w…

> I think this is a good example of what I was saying in the first post. It is the new benefit that the theory brings, not reproduction of every single result of the previous theories

Of course Schrodinger's model didn't reproduce the results of classical EM with regard to the atom. It wasn't supposed to, because those results of classical EM were wrong. In other words, there wasn't a correct "old theory" that covered the regime the Schrodinger model covered (the atom)--there was only a wrong "old theory".

As far as using Schrodinger's model plus classical EM theory to get results like emission line intensities, there also there was no correct "old theory"; there was only a wrong "old theory" (classical EM by itself, which did not predict emission lines at all, let alone their intensities--it predicted a continuous emission spectrum). Also, this hybrid classical-quantum model was known to be incomplete at the time; it was only used because nobody had yet figured out how to quantize the EM field.

> It is the new benefit that the theory brings, not reproduction of every single result of the previous theories

Once again, this is not the situation under discussion in this thread (gravitational waves). In the case you describe, the results of the previous theories were wrong in the regime the new model covered, so there was nothing to reproduce; there was no correct "old theory" for the new theory to compete with.

In the case of gravitational waves, we have a correct "old theory"--General Relativity--so any new theory that did not match that correct old theory would be a nonstarter. I am not aware of any case where a new theory was accepted as interesting when there was a correct old theory covering the same regime and the new theory did not reproduce its results.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#499

Post by effie »

pdonis wrote: post #498
effie wrote: post #495

Earlier quoted context omitted.

Schroedinger theory certainly was a new theory of the atom and later of molecules at that time, successfully competing and largely replacing classical EM models of atoms and molecules such as Larmor's theory of molecules, although it didn't cover the EM radiation aspect and EM theory needs to be used in parallel with Schroedinger's to get, say, intensities of emission lines. I think this is a good example of what I w…

> I think this is a good example of what I was saying in the first post. It is the new benefit that the theory brings, not reproduction of every single result of the previous theories Of course Schrodinger's model didn't reproduce the results of classical EM with regard to the atom. It wasn't supposed to, because those results of classical EM were wrong . In other words, there wasn't a correct "old theory" that cover…

> It wasn't supposed to, because those results of classical EM were wrong.

You're badly mistaken. Although nobody succeeded in obtaining the emission line frequencies of gases out of the classical EM theory, the theory did correctly give other results consistent with observations. One of them is the formula for emission intensity that connects energy radiated with second derivative of electric moment; it goes back to Larmor's work. This was the result the new theory would preferably reproduce or at least be consistent with. Wave mechanics wasn't consistent with it - the hydrogen atom oscillates indefinitely in wave mechanics. Schroedinger himself viewed this as a deficiency and planned to get back to it - check the ending part of his seminal papers on wave mechanics. The classical formula is taught to this day both in macroscopic EM theory and quantum optics courses, although there are some deficiencies and problems about the formula that Larmor did not know.

> In the case of gravitational waves, we have a correct "old theory"--General Relativity--so any new theory that did not match that correct old theory would be a nonstarter.

I do not think any physics theory could even be "correct" in the sense of Platonic ideals, but I do not know what you mean by "correct". I do not claim a new theory could completely replace the old one before it could deliver the same or better results. I claim theory has value and is accepted based on its new benefits, not its superiority in every aspect the old theory was superior before. Calling incomplete theory non-starter makes no sense to me, as all theories, including General Relativity, are incomplete.

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