The equivalence principle

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>[hal]: It is known from GR and confirmed by experiments, that gravitational field slows down clocks.
It is known from cyclotron experiments that acceleration has no effect on clocks.
It is known from GR "equivalence priciple" that the effects of acceleration are undistinguishable from these of a gravitational field.
Which one of the above is true?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

If you had read our June 15 <i>Meta Research Bulletin</i> article "21st century gravity", you would already have your answer plus the background to support it.

The problem is the phrase "gravitational field", which is being used with two different meanings. Sometimes it is used to mean "gravitational potential field (as in relativity)" and sometimes it refers to the "field of gravitational force" (as in dynamics). These are actually two physically different entities, even though the mathematics makes them appear to be a single entity related by the gradient function.

Physically, force and acceleration are linked. Likewise, velocity and potential are linked and have similar effects. But these two sets of phenomena are separate.

So a gravitational potential field slows down clocks, whereas gravitational acceleration per se has no effect on clocks. Examples of each operating in the absence of the other may be found at our web site in "Gravitational force versus gravitational potential", [url] metaresearch.org/cosmology/gravity/gravity.asp [/url]. You can also find a free PowerPoint viewer there for download if you need one.

So the first two points you cite are true. The third is true also, but has switched the meaning of "gravitational field" to refer to "force" instead of "potential". -|Tom|-

For Einstein gravity was only curved space due to the presence of the mass. Let's adopt this point of view and forget for the moment other possible gravity theories. Well, according to "equivalence principle" in this context, the acceleration MUST also curve space, bend light path (just like in Einstein famous mental experiment), etc. I am just trying to point to what seems a contradiction to me.

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>[hal]: For Einstein gravity was only curved space due to the presence of the mass.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

No, that is a common misunderstanding promoted by modern textbooks pushing the "geometric interpretation" of Einstein's theories, an interpretation Einstein himself never endorsed and that only became popular following Misner, Thorne and Wheeler (MTW)'s book "Gravitation" in 1970. Einstein's general relativity (GR) is a single mathematical theory with at least two, and possibly more, physical interpretations. Einstein preferred the "field" interpretation of GR, in which there is <i>no curvature of space</i>. There is curavture of "spacetime", which is a mathematical entity having no clear physical counterpart, but which is most definitely (and provably) <i>not</i> the same as space plus time. See [url] metaresearch.org/cosmology/gravity/spacetime.asp [/url].

Note that even MTW concede that no curvature of space is involved in GR (see p. 32), although subsequent authors simply ignored that fact. Note further that two of us have argued in print that the geometric interpretation of GR is now falsified and no longer viable. See “Experimental Repeal of the Speed Limit for Gravitational, Electrodynamic, and Quantum Field Interactions”, T. Van Flandern and J.P. Vigier, Found.Phys. 32(#7), 1031-1068 (2002). We were certainly not arguing that there is anything wrong with the mathematical theory, just with the fanciful "curved space" interpretation thereof.

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>Let's adopt this point of view and forget for the moment other possible gravity theories.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

To understand my previous answer, you must first appreciate that I was speaking generally about the ambiguous meaning of the expression "gravitational field", and not using a theory-dependent interpretation. If one does not define terms carefully, it is easy to arrive at a contradiction.

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>Well, according to "equivalence principle" in this context, the acceleration MUST also curve space, bend light path (just like in Einstein famous mental experiment), etc. I am just trying to point to what seems a contradiction to me.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

With your understanding (shared by many), you do indeed arrive at a contradiction. Those who do not know history are doomed to repeat it (or rediscover it). -|Tom|-

My understanding, or, in general, each possible understanding of gravity in this context is irrelevant. In other words, it doesn't matter what gravity really IS. Just to avoid semantic deflections, I propose we use expressions "gravity", "gravitation field", etc. keeping in mind the addendum WHATEVER IT IS.

Well, I suppose, now we can say:
- light paths bend in gravitational field (whatever it is) - veryfied by experiments
- clocks slow down in gravitational field (..) - veryfied by experiments
- acceleration has no effect on clocks - veryfied by experiments
- the equivalence principle says "gravitational field" <==> "acceleration"

The above is stated in very simplified form, but sufficient for the purpose of this discussion, I hope.

The question is - is there a contradiction, or not?

Are SR and GR conflicting theories? For example, when SR says that clocks run slow, then GR says clocks run fast. In SR, clocks in orbit run slow with respect to an Earth-bound observer. In GR, however, orbiting clocks run faster according to the lower gravitational field. It is sometimes argued that the effects of SR and GR on clock slowing are equal, but have opposite signs. How does one tackle this problem?

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>[Jan]: How does one tackle this problem?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

See the link to "Gravitational force vs. gravitational potential" at [url] metaresearch.org/cosmology/gravity/gravity.asp [/url]. -|Tom|-