# Liquid gravity

1. Feb 24, 2007

### verdigris

I've heard that some physicists think space-time is like a liquid.
So why aren't we dissolving in it?

2. Feb 24, 2007

### complexPHILOSOPHY

I was under the impression that space-time has been modeled in analogous fashion to a fluid but I don't think it's considered an actual 'liquid.' However, some sources might clarify this?

3. Feb 25, 2007

### verdigris

The point I was trying to make was this:when a real liquid like water gets between atoms,in particular ions,heat energy can be released (hydration energy).Since space exists between atoms,does it just exist there for free,or is some kind of energy released when it gets there?

4. Feb 25, 2007

### ZapperZ

Staff Emeritus
Er.. this is verging on crackpottery. What do you think "real liquid like water" is made of?

Please make exact citation of where you "heard" this from. If you can't find a legitimate reference, please re-read the PF Guidelines that you have agreed to, especially on over-speculative post.

Zz.

5. Feb 25, 2007

### Mute

It's obviously not a scientific journal, but the December 2005 issue of Scientific American's leading story is called "Echoes of Black Holes: What is spactime? Experimental models hint that it could be a kind of fluid". The article is by Theodore A. Jacobson and Renaud Parentani, professors at the university of Maryland and Paris, respectively. On the contents page the blurb about the article adds "Does the behaviour of sound waves suggest that spacetime is a kind of fluid?" In the article itself, light is compared to sound, and black holes are compared to Laval nozzles, etc. I didn't reread it, but I think it was more making analogies than claiming spacetime is literally a kind of fluid.

One of the papers mentioned after the article is by Parentani:

"What did we learn from Studying Acoustic Black Holes?"

http://arxiv.org/abs/gr-qc/0204079" [Broken]

Last edited by a moderator: May 2, 2017
6. Feb 25, 2007

### ZapperZ

Staff Emeritus
One needs to be VERY careful in interpreting such a thing. As a condensed matter physicist, I have seen many "analogy" between condensed matter physics and other areas of physics, including stuff in field theory, cosmology, and even the Standard Model. The Higgs mechanism itself came out of a condensed matter treatment.

But one should not confuse the "language" being used with something real until it is really "there". The OP is talking about fluid as in "water" here, flowing in between atoms! This is where misconception and misunderstanding occurs.

Zz.

Last edited by a moderator: May 2, 2017
7. Feb 25, 2007

### CarlB

This thread is just begging to be deep sixed. However, I've seen the occasional paper that thinks of spacetime as a fluid; black holes are sort of drains, I guess. For example:
http://arxiv.org/abs/hep-th/0604075

My problem with this sort of thinking is that light is a transverse wave, and fluids only support longitudinal waves.

In a solid medium, the speed of longitudinal waves is always greater than the speed of transverse waves. Typical factors are about $$\sqrt{3}$$ and depend on the details of the medium. For example, the speed of sound in pyrex is 5640 m/sec longitudinal and 3280 m/sec transverse, a ratio of $$\sqrt{2.957}$$

The standard model has matter as a combination of left and right handed waves that, if unaccompanied by the other, travel at speed c. Since this is the same speed as light, the implication is that matter is also a transverse wave. If one were to wish to look for experimental evidence of tachyons, a speed of $$c\sqrt{3}$$ would be a good place to start.

Before Einstein, there was some speculation that gravity was the longitudinal wave associated with the aether. The speed of gravity, however, was supposed to be infinite.

Last edited: Feb 25, 2007
8. Jan 3, 2008

### mncmbabcock

Why is Verdigris' question about fluid gravid "verging on crackpottery"? Just because it an idea is not the currently accepted theory by mainstream physicists, doesn't mean that it is wrong. Throughout history theories were accepted by scientists and then as better and better detection equipment and methods became available these were disproven. If one was to step away from the "I'm a physicist and you aren't so you are automatically wrong" equation you might get a fresh look.

Light is bent around a large body in space and it is accepted that it is the "attraction" of gravity that did it, however could it not be that the light was refracted? The larger a celestial body, the more space is displaced and therefore the greater the push of the fluid (hence gravity).

All I am saying is that blinders are just that, whether they are made from leather or from sheepskin.

9. Jan 6, 2008

### PhilosophyofPhysics

I believe the story is that "crackpots" were driving the knowledgeable members away. This was really bad, so the board cracked down on the crackpots. You cannot even get away with just kidding sometimes because someone might take it seriously.

The idea of a type of aether usually always attracks the mystical types. These are usually the ones that come up with crackpot metaphysical theories on how quantum physics, consciousness, spirit, and energy are all unified under one underlying theory of everything.

10. Jan 6, 2008

### Chronos

It's a backdoor aether theory - ascribing ponderable qualities to empty space - IMO.

11. Jan 6, 2008

### nicky nichols

I have been reading the recent work by Xiao-Gang Wen on string nets. I find his ideas very interesting and hope that he will continue to develop his theories with the additional underpinning of algebraic topology.

12. Jan 6, 2008

### sysreset

In defense of Verdigris, he posted his question the the forum called "beyond the standard model" which I hope will allow for lines of discussion slightly outside the mainstream. This allows people to poke and prod the mainstream ideas looking for new insights. Also, aether of sorts has made a major comeback in the form of dark matter and dark energy.

13. Apr 2, 2008

### vld

One can study both spacetimes and fluids by using the same mathematical tools (e.g., differential geometry and topology). That is where the analogy comes from. But in fluid dynamics people study "particles" as being stable configuration patterns of fluid (like vortices). By analogy, one can conclude that matter particles can also be made of spacetime fluid and, thus, that they cannot be "dissolved" in that fluid because they are made of it. This idea is actually very old. By googling you will find a lot of papers written by serious physicists discussing this possibility.

14. Apr 9, 2008

### mhill

I heard about this.. also that Einstein-Cartan version of General relativity is just a continuum model generalization of the dislocation theory (metallurgy)

15. Apr 11, 2008

### vld

Does Cartan have something to do with metallurgy? As far as I know Einsten doesn't. Since in Einstein-Cartan's theory singularity is avoided because of negative pressure due to torsion, does this mean that it is more general then GR, which is known to have a limited domain of validity (failing in the point of singularity)? Do you have any introductory reference about the dislocation theory?

16. Feb 9, 2009

### SodaBiscuit

Yes it is sad that for example the crackpot Tesla came up with such theories. If Tesla had come up with truthful theories, then at least he would have invented something useful in his life. But since he was such a crackpot that Tesla, he ended up inventing nothing useful for society. If only he had learned proper, truthful, and correct physics - only then would he have invented anything at all that was useful to us. I mean you cannot even take the AC motor seriously - it was pure crackpottery and a fraud from day one. It does not even work, for one thing!