Towards a new test of general relativity?

European Space Agency ^ | 23 March 2006 | Staff

[Southack]

"Clocks do slow down due to gravity, as they also do when accelerated. Yes, this has been measured, and the effect is exactly as predicted by special relativity."

Special Relativity and Gravity...are you certain?

[RightWhale]

many on FR who believe that taxes should not be spent on R&D

Yup. Massive gov't spending on science began during WW II. By a massive coincidence, American pre-eminence in science began during WW II. Private spending on science is the way it was done before, when America was not pre-eminent in science.

[Conservative4Ever]

For Women: gravity on butt and boobs=age

[AdmSmith]

Science does not bet. It does formulate and fly hypotheses for others to shoot down by observation and experiment.

Yes that is true, but I have the right to bet on the outcome of the experiment.

[PatrickHenry]

This shows the effect of gravity on clocks (using the term "clock" loosely) which can be detected in gravity differing as little as that between the roof and basement of a building: Pound-Rebka experiment.

[PatrickHenry]

Special Relativity and Gravity...are you certain?

In this case, yes. Acceleration and gravity have the same effect on clocks. The principle of equivalence. If I'm wrong, I expect that one of the heavyweights will correct me.

[RightWhale]

It is kind of second-order weird when people like Hawking bet on a theoretical result and they are the one doing the theoretical calculation and they lose the bet.

[Alamo-Girl]

Thanks for the ping!

[Southack]

"In this case, yes. Acceleration and gravity have the same effect on clocks. The principle of equivalence. If I'm wrong, I expect that one of the heavyweights will correct me."

I would have expected Special Relativity to deal with the kinematic effect, but that General Relativity would have dealt with the Gravitational effect.

[lafroste]

Yes. The gravitational field affects the flow of time.

I don't mean to be dense, but how do we know that it is not the other way around?

BTW: Thanks for the interesting posts, I'm on my way out for a while.

[Robert A Cook PE]

Things that make you go "hhhhhhhhhhhhhhummmmmmmmmmmmmmmmmnnnnnn....."

[RightWhale]

Of course we should use whichever coordinate system seems most workable. For gravitational fields we have Riemannian space, and that seems handy enough. If time fields use the same kind of field, it would not matter as a practical thing. Whichever is convenient and attracts funding is the way to go.

[AdmSmith]

I don't see how. This effect -- if it's real -- happens with a rotating superconductor. Are there any such objects that astronomers could observe? If so, then you've got a point.


Here you have an article about binary pulsars; two rapidly rotating highly magnetized neutron stars. http://relativity.livingreviews.org/Articles/lrr-2005-7/

and here a primer on neutron stars http://www.astro.umd.edu/~miller/nstar.html

[InterceptPoint]

It's not clear. The article says they used "Small acceleration sensors" to detect whatever it is they detected. I assume those are something like Robert Forward's mass detectors, but I'm guessing. Then they attribute their unexpectedly high readings to gravitomagnetism. It's a bit conjectural at this point. But if they've really detected something, it certainly requires an explanation.

I agree.

I'm not sure how Bob Forward's Mass Detector worked but I thought he was looking for gravitational waves and never actually found them.

These guys must be using some sort of mass detector that shows a deflection from the vertical in the presence of mass. And that deflection changes when the superconducting ring is accelerated. I'm just guessing but that's what it sounds like to me.

[Quark2005]

I would have expected Special Relativity to deal with the kinematic effect, but that General Relativity would have dealt with the Gravitational effect.

SR can only deal with the kinematics of constant velocities. When accelerations or gravitational fields are involved, GR is needed; and in its framework, an accelerating reference frame and gravitational field are equivalent, just as PH stated.

[Erasmus]

I would expect that two perfect clocks, one at sea level, one at 175,000 ft orbit would read one second different after about 86 years (the clock at sea level lagging the one in space).

Not to pick nits, but you better make that at least a million feet.

< ]8^0)

[Southack]

Better check twice which clock will be lagging, too.

[Southack]

"When accelerations or gravitational fields are involved, GR is needed; and in its framework, an accelerating reference frame and gravitational field are equivalent, just as PH stated."

Was GR or SR cited in that post by PatrickHenry?

[Calvin Locke]

PBS ran a series in honor of Einstein's 100th, and the US Navy did indeed take a matched pair of cesium clocks, and fly
one of them around for a while, and yes, the one in the air "slowed".

I didn't think of using the Earth's rotation at different heights to do the experiment. Pretty constant v for each clock...

[UnbelievingScumOnTheOtherSide]

I think synchronized clocks (atomic clocks, not your everyday alarm clocks) will diverge enough to be detected when one is at ground level and the other is taken to the top of a tall building.

Unless the tall building is at the north or south pole, you have to account for the fact that the top of the building is moving faster than the bottom as earth's rotation carries it through a larger arc even though they are not moving with respect to each other or you are counting the same effect twice. Right? (If the building were were at the equator and 2.561 billion miles high, the top would be moving at the speed of light requiring infinite gravity to hold it.)