Getting a theory of everything by ditching tenet of physics

[n2doc]

A few recently published papers indicate that the long-running attempt to unite quantum mechanics and relativity might be finally seeing some compelling progress. A long-cherished tenet of physics, the Lorentz Invariance, is the first casualty.

By Chris Lee | Last updated June 11, 2009 10:25 AM CT

Every article on quantum gravity begins the same way. On the one hand we have quantum mechanics—excellent at describing the very small and intrinsic lumpiness of the universe—and on the other hand we have general relativity—excellent at describing gravity, but it relies on a smooth universe. At some point the two meet, and just like Manchester United supporters and Liverpool fans, they just don't get along. Luckily for the universe, tire irons haven't been deployed to settle this incompatibility.

A pair of unrelated papers, which appeared in Physical Review Letters, and a News and Views article in Nature Physics all indicate that progress is occurring, but it is coming at the expense of a long-cherished tenet of physics, called the Lorentz Invariance.

Progress in uniting quantum mechanics with general relativity has typically proceeded along two lines. Option one is to generate seemingly outlandish ideas, such as string theory, loop quantum gravity, and their brethren, which resolve the problem by positing the existence of things as yet unobserved. The more sedate approach is the rapid-fire production of grand unified theories, which are neither "grand" nor "unified" and, completing the trifecta, may not warrant the moniker "theory" either, since they simply don't work.

more:

http://arstechnica.com/science/news/2009/06/getting-a-theory-of-everything-by-ditching-tenet-of-physics.ars

[scubadude]

1. Well, if they use the inflationary model at all then Lorentz Invariance, is the second casualty

The first IMHO was lightspeed. The early universe had to expand at superluminal speeds for the inflationary model to work. I would say that was the first thing to go. Light speed as the top limit.

Casualty 1, light speed as the upper limit of motion within our universe.
Casualty 2, Lorentz Invariance.


Now it's up to the physicists on the site to tell me what I got wrong. The hard part will be getting me to understand it! LOL But if they succeed everyone will understand.

Scuba

[Indenturedebtor]

2. Isn't lightspeed as the upper limit already dead?

How could paired particles communicate faster than light if lightspeed were the upper limit?

I'm not a big supporter of those who try to explain EVERYTHING in terms of particles, but clearly there is information being shared at a speed greater than light.

So while lightspeed may well be the limit for matter... matter and energy are the same cosmic goo in different states so in my completely plebian opinion lightspeed is dead anyways.

I really like this treatment. It has a simple beauty to it that feels right.

[caraher]

4. Haven't had a chance to look at the papers yet

and I suspect they'll mostly be over my head anyway.

But as for the lightspeed thing, entanglement-related phenomena do not imply any superluminal *information* sharing. It cannot be used to send any kind of signal faster than the speed of light. It is possible to interpret experiments on entangled particles in a way that implies superluminal *interaction*, but this is not the same as transmitting information. It's also just an interpretation; other interpretations of the same experiments exist that do not carry the same implications. What's true under all interpretations, though, is that one cannot transmit information this way faster than the speed of light.

I know less about inflation and the fact that its rate is calculated as superluminal always bothered me. I imagine that there may be an "out" there in that what was "inflating" was spacetime itself - I'm not sure exactly how that would make a difference, but it strikes me as plausible that it might.

I'm more curious about exactly how Lorentz invariance breaks down in these theories. Is it on certain distance scales? How does it fail? Is there a different invariant quantity for which the spacetime interval is simply a good approximation in most circumstances? And most important of all, what experiments should be able to see the difference?

[Indenturedebtor]

8. Ok so can you change the state of paired particles more than once?

Observe them and then unobserve them?

So that you could seperate them by some distance, observe the particle on one end, have that state transmitted to the other particle... then restore the uncertainty while maintaining their coupling, and do it again?

I can see how in the first pairing-seperation-changing of states you wouldn't really be traveling faster than light as you are sort of "storing up potential energy" by slowly moving the particles apart.

but if you could return them to an undetermined state while maintaining the pairing, then the potential energy would have already been spent in the first "superluminal" transmission of information, and on the second you would truly have a superluminal transmission.

Does that make sense?

What do you think?

[caraher]

10. The trouble is measurement breaks the entanglement

Once you look at either particle its wavefunction changes to a definite state of whatever aspect of it you just measured. The distant particle with which it is entangled also changes state. This new state for the two particles is no longer entangled, so there are no second measurements. You could re-entangle the particles, in principle, but doing so will involve doing something that is at best going to involve an interaction mediated by something moving at lightspeed.

I think I understand what you are proposing, I just don't think it works because of the collapse postulate and the fact that entanglement is generally fragile and not easy to generate in useful ways on demand.

[Indenturedebtor]

11. Ah ok... so in simple terms it is "potential energy" that allows this seeming breach

in the speed limit... by moving the particles once they've been paired you are building up the potential for them to share information at beyond the speed of light. I wonder by this goofy conceptualization then - what would happen if you moved the particles apart at close to the speed of light and then forced one of them to "pick" a state.

Or is it more a question of - the particles have no definitive state within the universe, as their possibilities haven't collapsed, and you're really still operating somewhat outside of the bounds of space-time by confusing their "identities", and therefore when you couple them and force one of them to pick a state - when they choose a state each of them then has an identity and that identity must then be separate moving forward... therefore they cannot be recoupled as they each have defined their place in our causal universe. Simply existing in a specific state in a specific space-time has then given each of them a separate identity, and they must again exist in a minimally proximal space-time region to have their identities "re-confused" to the point where they can be coupled again?

Is it more a question of undifferentiation than it is of truly joining them together? Do they simply exist on the boundaries of existence in space time to the extent that they have no true identity in space-time, so when you pair them you have confused space-time to the extent that is hasn't placed them in the causal chain of the universe until you force these particles to collapse their possible states (ie place, energy state, time, etc) in space time?

Is the game really being played on space time and not the particles themselves? In that way it wouldn't be information passing between the particles, but simply a shared "confusion" on the part of space-time itself. Space time "knows" that there is an unquantified link in the causal chain, but until an element of that causal chain has definitively interacted with that "link", space-time hasn't fully absorbed this unknown entity into itself?

Does that at all make sense or have I had too many beers and blunts?

[caraher]

14. Probably some of the weirder-sounding suggestions are more accurate

It really has nothing to do with potential energy; for instance, if you entangle the polarizations of two photons the energy transport occurs independent of the results of your polarization measurement.

You're more on the right track where you say, "the particles have no definitive state within the universe, as their possibilities haven't collapsed." It's not exactly about whether the particles have separate identities since you can also entangle distinguishable particles. If the particles are not entangled, one can measure some property of each and the results will be independent of one another. But when they are entangled, when you measure one particle that changes the possible outcomes of a measurement on the other - instantly.

You asked, "what would happen if you moved the particles apart at close to the speed of light and then forced one of them to "pick" a state." This is an experiment done many, many times on photons, which of course move apart at the speed of light. In the experiment one measures a property (frequently polarization) of one, which in effect forces it to pick a state. The wavefunction changes from the entangled state to one where the one you measured is in a pure state corresponding to the result of the measurement, and the other one is now in whatever state the measurement of its partner would dictate. What makes this so interesting is that there is pretty much no way to maintain that the entangled wave function is merely a measure of our ignorance. (In other words, suppose I had a red marble and a blue marble and placed them in identical boxes. You fly to Tokyo and I fly to London and when you open your box and see a red marble, you know I must have a blue marble in my box. The situation with photons is fundamentally different from that. If someone "prepared" color-entangled quantum marbles they would be neither red nor blue until one box was subject to a "measurement" (one of us looking, or really, when any physical process occurs that would depend on the marble having a definite color; consciousness really is not necessary for quantum "measurement"). There is a mathematical test of the difference known as violation of a Bell inequality, and many tests of Bell inequalities on entangled photons support the indeterminate state picture and not the "well, it was really blue all along, we just didn't know until we looked" model.)

As far as re-entangled them, you write, "Simply existing in a specific state in a specific space-time has then given each of them a separate identity, and they must again exist in a minimally proximal space-time region to have their identities "re-confused" to the point where they can be coupled again?" That's pretty close. You don't absolutely need to bring them together again. But they will at least need to interact with something that has a common source; imagine two atoms widely-separated that each interact with one photon of an entangled pair; something like this could re-entangle them. "Remote state preparation" is an active area of research, as is "teleportation" (and sometimes their definitions blur). And again, it's not strictly speaking about particle identity. Mathematically, entanglement is about the form the wavefunction for the entire system of particles can take. If you can write it as a wavefunction for one particle times the wavefunction for the second particle... times the wavefunction of the Nth particle, the particles are not entangled. The particles can be very different - say, a photon and some atom - yet have a joint wavefunction that cannot be written as such a product.

[Indenturedebtor]

16. Thank you :D n/t

[qazplm]

6. paired particles dont really

"communicate" any real information, it's just that when you observe one, you collapse the other into the opposite instantly.

You can't transmit any information that way.

So no C is still C.

Thus far.

[Indenturedebtor]

7. Couldn't you transmit info that way by sending one across the universe

So if you had say 5 paired particles you could go 01011 - corresponding to how you determined their states?

Like I said, I'm a plebe so please explain if my reasoning is wonky.

[Salviati]

15. Nope, because you can't predict or control the result of the measurement

As mentioned above, the mechanism involved in entanglement is fundimentally different from a process that always creates a pair of red and blue marbles, which you then observe later, but that analogy can serve to explain why you can't use this to send messages.

Suppose 5 entangled pairs were created, you leave with 5 boxes of marbles and your friend does as well. Once well seperated you open your boxes and find red, blue, red, blue, blue and thus know that your friend must have blue, red, blue, red, red. But since each box was random, and you have no control over what the outcome is, only that there IS an outcome (by opening the box), there is no way you can influance in any way the outcome of your friends boxes.

[Indenturedebtor]

13. Ok but quite aside from the other issues - could you not convey info that way?

C completely aside? Once it is collapsed, is it's state not observable?

[Odin2005]

9. the speed limit does not apply to the expasion of space itself

When the speed of light "C" is said to be the "cosmic speed limit" what is meant is that massless particles (like photons) always travel at C and that anything with mass cannot reach that speed because to do so would require infinite energy.

[Indenturedebtor]

12. But if you operated at the boundaries of space-time - outside of the causal chain

then you wouldn't be bound by those rules? Please see my beer-addled questions above... and consider the fact that quantum particles pop in and out of existence constantly. Could the particles that comprise our fundamental particles also be doing the same thing but at a higher "frequency"... so when they are observed they are forced into the causal chain of our universe?

Per my questions above, could this simply be a matter of "identity" - identity being a place and time in the causal chain that has defined our universe?

Could this all be explained by looking at the universe as a grand flexible equation - that has to constantly adjust to the exits and entrances of particles that manage to break some sort of reality threshold by sufficiently resonating with our causal and material universe?

As in Judaism - the creation song of the universe? Perek shirah. Not peddling religion, just using analogy is all.

More beer for me... wheeeeeeeee :D

[necso]

3. There are other issues.

But an adequate treatment is impossible here.

Briefly, even if a seemingly-accurate unified-theory is arrived at (and holds up to scrutiny), at best it represents an integration of what we now "know" and "understand".

But there may be more to learn; what we "know" may not be correct; and we may not understand what we think we do.

Indeed, our experience (perceived, other) of (some) things may have much to do with how we look at them, how we think about them, how we perceive them, how we approach them, how we treat them -- and with the effects of things we don't perceive, recognize, or understand. That is, we may be biasing ourselves in ways we don't realize.

And the question arises, why the seeming obsession with unification?

Now, don't get me wrong, (seeming) contradictions play a huge role in how I look at things. (And I believe in pursuing potentially important contradictions until they are resolved... or dying with them in mind.)

But sometimes you have to live with contradictions.

And the search for unification appears to me to have taken on even larger proportions than a (seeming) contradiction of this magnitude would warrant.

Is this another search for god? A matter of course?

And what does this say about the direction of (the related, at least) science?

[Joe Chi Minh]

5. The desire to find a unified principle seems to me to suggest quite the

opposite: dispensing with any notion of a "deus ex machina"; a closed system that doesn't need no steenking god.