Frame-dragging confirmed!

[Evil Dr Ganymede]

Earth's spin warps space around the planet, according to a new study that confirms a key prediction of Einstein's general theory of relativity.

Full article:
http://www.space.com/scienceastronomy/w ... 41020.html

[Cham]

This is a major finding. I was waiting for this result since a long time. The Lense-Thirring effect was confirmed with many astrophysical observations before, but the systematic errors were pretty high. Now, the new results were made by Earth orbiting satellites, so the results should be much more acurate. There's another experiment running with another satellite, I don't remember what is its name.

By the way, it could be cool to have a 3ds mesh and a .ssc file for the two LAGEOS satellites orbiting the Earth in Celestia. The satellite is really simple : a perfect sphere with small mirrors, a bit like a gulf ball. I don't have the tools to make the mesh myself.

[Cham]

There are two interesting Lense-Thirring predictions from General Relativity :

Suppose the Earth is a perfect sphere sitting in space, and spinning around its center with the SPIN angular momentum "S". You put a satellite on a circular orbit around the Earth, with an ORBITAL angular momentum "L". The orbital plane is oriented at 90 degrees from the Earth's equator, and let the satellite spin around its own center with a SPIN angular momentum "s". In newtonian gravity, the quantities "L" and "s" are not influenced by the Earth's spin "S". Of course, "L" depends on the Earth mass and on the distance, but "s" is totally independant from the Earth. They are constant (in the Newton theory). But in General Relativity, this isn't so. The Earth's spin "S" will "drag" the orbital plane, so "L" change its orientation with time ! This is what the new result is showing experimentally (LAGEOS satellites). Also, the satellite spin "s" will change its orientation in time, because of "S". This is another Lense-Thirring effect which isnt confirmed by the LAGEOS satellites. Another (ultra-precise) experiment is actually running to show this effect. I can' wait the results !

[Scorpiove]

The other sattelites name is "Gravity Probe B" . It uses Gyroscopes. Also "Guinness world records" has confirmed them as "The most round objects in the world". Also "Gravity Probe B" has to be one of the coolest names given to a sattelite .

[alphap1us]

This is a major finding. I was waiting for this result since a long time. The Lense-Thirring effect was confirmed with many astrophysical observations before, but the systematic errors were pretty high. Now, the new results were made by Earth orbiting satellites, so the results should be much more acurate.

Actually a think both of these experiments are a big waste of money. It's not like frame-dragging was a controversial topic. I mean, no one realistically expected that the results would be otherwise. It would be significant if it were disproved, but to no one's surpise, relativity was confirmed...again. I do like thinking about those perfect spheres, though.

Joe

[Evil Dr Ganymede]

Actually a think both of these experiments are a big waste of money. It's not like frame-dragging was a controversial topic. I mean, no one realistically expected that the results would be otherwise. It would be significant if it were disproved, but to no one's surpise, relativity was confirmed...again. I do like thinking about those perfect spheres, though.

What, so you'd rather that everyone just kept on guessing that frame-dragging was real? There's a difference between "oh, it surely must exist" and "it definitely exists". And you can't really do research based entirely on assumption

[Cham]

This is a major finding. I was waiting for this result since a long time. The Lense-Thirring effect was confirmed with many astrophysical observations before, but the systematic errors were pretty high. Now, the new results were made by Earth orbiting satellites, so the results should be much more acurate.

Actually a think both of these experiments are a big waste of money. It's not like frame-dragging was a controversial topic. I mean, no one realistically expected that the results would be otherwise. It would be significant if it were disproved, but to no one's surpise, relativity was confirmed...again. I do like thinking about those perfect spheres, though.

Joe

This is a wrong attitude toward Science. General Relativity made a great prediction, and it is the role of science to prove or disprove the prediction. This is how science is working. It's certainly NOT a waste of money. What if the prediction was false ? If the experience wasn't done, we couldn't know it !

And there are many variations on relativity theory. Some alternative theories are predicting other effects and some partial Lense-Thirring effects. Those experiments may permit us to know which one is true.

And then, what about the gravitationnal waves ? Should we make any experiments ?

[alphap1us]

Hi guys,
I think you have to conisder the issue with regard to the limited resources that are available for experimental sicence. I was not suggesting that no one should test out experimental theories, only that there were other theoretical consequences that are more controversial and should be given priority over an experiment that was so expensive, difficult and agreed upon. If it cost 5K 50K or even 500K for this experiment it would have been worth it, just to cross it off the list, but this project cost much more than $150M. Think of all the table top experiments or even a few observatories that could be created with that money. It just doesn't seem worth it to me, though I welcome any comments.

Joe

[t00fri]

Hi guys,
I think you have to conisder the issue with regard to the limited resources that are available for experimental sicence. I was not suggesting that no one should test out experimental theories, only that there were other theoretical consequences that are more controversial and should be given priority over an experiment that was so expensive, difficult and agreed upon. If it cost 5K 50K or even 500K for this experiment it would have been worth it, just to cross it off the list, but this project cost much more than $150M. Think of all the table top experiments or even a few observatories that could be created with that money. It just doesn't seem worth it to me, though I welcome any comments.

Joe

On the one hand it is certainly true that the mission of science is to definitely clear up important open questions by means of experiments, even if they are expensive.

Since such pioneering experiments become increasingly expensive, I think Joe's view cannot be discarded either:

In the coming years with gravity & general relativity having become mainstream subjects, we will have to live with increasing amounts of competition as to the experiments that can actually be done.

In my view, priority should definitely be given to experiments that (with some luck) could open entirely new windows of knowledge!

Two extreme examples:

a) Tests of CPT invariance. An old very basic assumption in quantum physics. If violated, the signatures would be extremely hard to detect...Still, it's a very fundamental issue!

b) Examples of "in" experiments that would dramatically open new windows:

-- Dark Matter searches (Supersymmetric particles?)
-- gravitational waves
-- search for Supersymmetry at colliders
-- production of black holes at particle colliders?
-- hunting for the primordial cosmic neutrino background
via ultra-high energy cosmic ray experiments. In
analogy to the famous cosmic microwave
background experiments (BOOMERANG, WMAP,...)
this would probe the Universe when it was only
1 second old!
-- what is the nature of the neutrino mass? Is it
"Majorana" or "Dirac" type? {This could be decided
via the neutrinoless double beta decay)

Clearly I would vote to realize all experiments of category b) before turning to a).

Bye Fridger

[Cham]

There are two major predictions of General Relativity which needs to be confirmed, before the theory could be put "in stone" :

1- Lense-Thirring effect,
2- Gravitationnal waves.

There are many concurrent theories which are fighting against GR, especially the scalar-tensor theory of Brans-Dick and some variations. Those theories are predicting different things for 1 and 2 above. So the LAGEOS, GRAVITY PROBE and LIGO experiments are REALLY important.

It is not only about theories, it's about real concrete applications to the real world, like the GPS satellites and its future incarnation.

It's funny how GR was an obscure theory, some 75 years ago, with very few searchers working with it. Most physicists were working on quantum theories at that time. Now, it's almost the reverse. GR has been tested with a much higher degree of accuracy than the quantum theory. However, GR still needs some other testings in some areas (1 and 2 above). Okay, as a relativist, I may be a bit sold to GR

[t00fri]

...
There are many concurrent theories which are fighting against GR, especially the scalar-tensor theory of Brans-Dick and some variations.
...

Cham,

but really, there are only /very few/ scenarios that "big science" is taking seriously. Among them in first position : (Super)String theory. The scope is so much larger than just GR! We talk here about the most ambitious embedding of GR, Supersymmetry, Cosmology and the whole of particle physics into a single theoretical framework that for the first time also promises a bona-fide quantization of gravity.

I think nowadays there is not much point anymore to discuss issues like the validity of classical (non-quantized) GR in an isolated manner.

I give you a simple most impressive example:

When you address the most important question of what happens close to the Big Bang singularity, classical GR just has to give up. Related and even more pressing is to find a natural explanation in this regime for the right /initial conditions/ required for Inflation to work. These have to come out of a truly dynamical non-perturbative quantum framework rather than being set artificially by hand. You sure know that they appear thoroughly "unnatural" within the usual framework.

Playing merely with classical GR in this context, would be more than naive, since it cannot lead anywhere due to its intrinsically limited scope..

Gravity becomes highly non-perturbative at such scales when the universe was tiny. People recently found that String theory provides in contrast a controllable stable framework for discussing the transit through such space-time singularities like the BB. It is now quite probable that the BB was NOT the beginning of time, but just a transit into another "phase" of the Universe.

For large distances, the familiar GR is completely contained in String theory in the sense of an asymptotic limit.

Bye Fridger

[Cham]

To be honest, I don't "believe" at all in string theories. I think people are losing their time on that one, but ... I'm not a specialist on string theories so I wont argue on them.

Anyway, have you read Paul Davies, and John D. Barrow (of course, I presume) ? Apparently, they don't "believe" in string theory either. I share their opinion.

I'm personnally more inclined to "believe" in loop gravity or Penrose's twistor theory than on a string theory.

[t00fri]

To be honest, I don't "believe" at all in string theories. I think people are losing their time on that one, but ... I'm not a specialist on string theories so I wont argue on them.

Anyway, have you read Paul Davies, and John D. Barrow (of course, I presume) ? Apparently, they don't "believe" in string theory either. I share their opinion.
....

Cham,

I think the main issue is really not one of "believing" at this time.

What creates the enormous polarization worldwide in favor of String theory is its SCOPE. String theory is simply the only known framework that is both extremely beautiful (mathematically and as a physical theory) and is potentially able to encompass all known forms of interactions and symmetries in a UNIQUE theory.

Tell me another theory that might have the POTENTIAL at least to tell us why we live in 3+1 and not e.g. in 27 space-time dimensions!

And last not least: "Big Science" does not care a bit whether you or I believe in String theory or not

I'm personnally more inclined to "believe" in loop gravity or Penrose's twistor theory than on a string theory.

For God's sake, what do you mean with "loop gravity"?? The whole point is that loop formulations of gravity are hopelessly divergent unless you use its String embedding! Gravity is highly non-renormalizable because loops are so badly divergent...

Bye Fridger

[Cham]

Well, to date, string theory hasn't been able to predict a single thing that could be verified experimentaly ! It's not yet verifiable ! It is not real science, until it can make a usefull claim. Retrodict that space-time has 3+1 dimensions because of that and that isn't really usefull to me. After 25 years of hard work, sheesh, what a pack of bull is that theory

You are wrong on quantum loop theory. It's a serious candidate for quantized gravity, and it may succeed before string theory (if you're a true believer)

[t00fri]

...
Anyway, have you read Paul Davies, and John D. Barrow (of course, I presume) ? Apparently, they don't "believe" in string theory either. I share their opinion.
...

Cham,

do you mean this one?

J.D. Barrow, (ed.), P.C.W. Davies, (ed.), C.L. Harper,
(ed.), SCIENCE AND ULTIMATE REALITY: QUANTUM THEORY, COSMOLOGY, AND COMPLEXITY.
Cambridge, UK: Univ. Pr. (2004) 721 p.

No, sorry, I usually read original papers. No time for 721p books . Neither of the two authors are authorities in String theory, i.e. have written papers in that field. So, they can hardly judge String matters in their full scope, I suppose.

Bye Fridger

PS: Prof. Ann C. Davis, also of Cambridge Univ., would be a much better person to make statements about Strings...

[Cham]

Well then, you sound a bit like a string theory believer to me

Are you working in that field ?

[t00fri]

...
You are wrong on quantum loop theory. It's a serious candidate for quantized gravity, and it may succeed before string theory (if you're a true believer)

Cham,

could you please quote a few /well-known/ scientists who have worked on "loop gravity"? I would really be curious, since I know most relevant people in this game.

Bye Fridger

[Cham]

t00fri,

the only things I have read on quantum loop gravity are several articles from http://arxiv.org/archive/hep-th and http://xxx.lanl.gov/archive/gr-qc.

I'm not really that interested in QLT or String Theories (I'm really not a "believer"), so I can't tell you a name (except Witten and Green in String Theory).

IMHO, physics is not yet ready for that stuff. We have to learn much more on "basic" stuff like the quantum vacuum (Casimir effect, for example), inertia, and such things.

I think the String Theories and Loops are just speculations. Not science. There's a lot of "magic powder" which is coming from the guys working on those theories. This isn't surprising me, they try to advocate their researches which are sooooo long to do !

[alphap1us]

Wow, I saw 17 replies and thought that people were teaming up to tear me a new one. Little did I know that Fridger had come to my aid...

It should make you happy, Fridger, that I just got a job making droplet detectors for a physicist trying to detect WIMPs. I don't know much about it yet, but I am excited to start.

Cheers,
Joe