# Quantum correction to Friedmann equations predicts no Big Bang

Discussion in 'Mayberry Lounge' started by klnOmega, Aug 7, 2015.

1. ### klnOmegaBannedBanned

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http://www.sciencedirect.com/science/article/pii/S0370269314009381#

Basically the gist is this. In General Relativity, gravity is treated not as a force, but as curved space-time. Instead of thinking of the earth as tugging apples down to it, think of the earth as sitting on a giant trampoline, and the dimple it makes in the trampoline is the distortion of space. That means that equations of motion in general relativity aren't written for flat spaces, like you made have done when figuring out classical trajectories using Newtonian mechanics in high school, but rather on curved spaces. Now in the absence of external forces (and remember, gravity isn't a force in General Relativity), particles will follow the shortest line between themselves and their destination. The shortest line on curved spaces isn't a straight line, it is called a geodesics (like how airplanes don't fly straight their destination). When the equations in General Relativity are solved, they are solved by treating particles with no external forces applied to them as moving on geodiscs, and these results predict that the universe was once collapsed into a point-like state.

Now shelve that for a second. Bohmian mechanics is an area I'm intimately familiar with, as do development on Bohm's theories. Bohmian mechanics differs from the popular Copenhagen interpration of Quantum Mechanics you are used to. Under Bohmian mechanics, particles do not existed in "all possible states" and "collapse". Instead, in Bohmian mechanics, quantum particles are actually a field of "fluid-like" particles, and their positions and momentum are set and defined. The fluid then evolves in time according a "Guidance equation", which is determined by the systems wavefunction. An equation for the motion of the individual fluid particles was derived independently by Bohm and deBroglie, and looks almost likes Newtons second law (F=ma), except there is a second force between fluid particles, that also depends on the amplitude of the wavefunction, called plainly, the quantum potential.

What the above authors did was merge Bohmian mechanics into General Relativity. Bohmian particle trajectories don't necessarily follow the relativistic geodisics because of the the quantum potential. So they derived Friedmann's equations (the central equations in expansion of space time and the prediction of the big bang) using the Bohmian trajectories instead of geodesics, and what they see is that there is a second term, a radiation term, arising. Basically as the universe crunches, the quantum potential explodes and causes particles to radiate until the radiation pressure kicks off new expansion. Likewise, when the universe expands to much, the quantum potential will serve to pull it back down. The result isn't a Big Bang or a Big Crunch to a singlularity, but rather an infinite oscillation of small universe to large universe to small universe again, forever onward.

Anyway, thought it was interesting. Feel free to discuss the origins of the universe.

Further reading if you are interested:

Background:
https://en.wikipedia.org/wiki/Raychaudhuri_equation
https://en.wikipedia.org/wiki/Geodesics_in_general_relativity
https://en.wikipedia.org/wiki/Friedmann_equations
https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory

Very digestable and easy description of Bohmian mechanics: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.82.5190
A longer but still readable description from Bohm himself: http://www.sciencedirect.com/science/article/pii/037015738790024X#
Quantum potential in dense Bose-Einstein condensate predicts no singularity, gives correct cosmological constant: http://arxiv.org/abs/1411.0753

Last edited: Aug 7, 2015
2. ### BKMMAFANSilver Belt

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Does Bohman Mechanics include pilot-wave theory? Also, once inflation theory was actually shown to be correct wasn't it basically impossible to trace the universe any further back in time (Planck Time?)

It's my understanding that the Copenhagen Interpretation is still the dominant theory. Interesting.

3. ### IDLSteel Belt

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The universe.. It breathes..

I like this better than the big bang.

4. ### klnOmegaBannedBanned

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Bohmian mechanics is an example of a pilot-wave theory. Basically substituting the polar form of the wavefunction into the Schrodinger (or Dirac) equation, and separating real and imaginary components yields two equations. The first is the guidance equation, which dictates how the wavefunction evolves in time. The second is the quantum Hamilton-Jacobi equation, where the quantum potential is seen. Under Bohmian mechanics, the wavefunction is acting a pilot-wave evolving according to the Guidance equation, and dictating the motion of the quantum fluid particles through the quantum potential.

Yeah, but the universe never even collapses that far under the new theory. It isn't allowed to collapse further than the Bose-Einstein condensate phase.

5. ### BKMMAFANSilver Belt

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Is Bohmian mechanics compatible with determinism (or does it require it)?

Thanks for the responses.

6. ### BVGBannedBanned

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I'm leaning more towards the "this is all just a simulation" theory

7. ### RightKneeBlue Belt

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Jesus is God confirmed..

8. ### Medusas WeaveBlue Belt

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Liking it doesn't make it true. Fact is that the universe is going to end in a heat death and that the universe was started during the big bang.

9. ### Rod1Titanium Belt

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LOL at stating FACT when it comes to discussing the end or beginning of the universe.

Anyway, what i dont get, is that if the universe is infinite, does it means that complete entropy would already set in somewhere along the road?

Or maybe Newton was right and the creator winds up the clock once in a while.

10. ### ultramanhyataReclimbing Like Mountain

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When theists ask atheists where the universe came from, if the atheists say, "It's always existed," I wonder if the theists will laugh as hard at them as the atheists laugh at the exact same answer to their challenge: "Where did God come from?"

11. ### EndlessCriticSteel Belt

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Dude, I'm a lawyer, not a fuckin' genius. Get that shit out of here.

12. ### klnOmegaBannedBanned

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The theory is explicitly deterministic. Wavefunctions evolve in completely deterministic fashion, and "fluid particles" follow completely determined trajectories.

13. ### klnOmegaBannedBanned

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It has the same entropy problem that almost every cyclic model does. The answer is the same as with them...some dark energy fixes it. I never understood it.

One that works really well for some cyclic models is that if the universe expands until it becomes a uniform photon gas before collapsing, then the entire expansion process was adiabatic and isentropic, and wouldn't violate the second law. The only issue is that almost no cyclic models (including this one) think the universe would expand to a uniform photon gas before the collapse.

Last edited: Aug 7, 2015
14. ### Rod1Titanium Belt

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Damn, i wish the world was simpler, it kind of makes me want to believe in God again and go to church every sunday.

15. ### Medusas WeaveBlue Belt

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yeah, holy shit at me saying the theory of the universe which is the most accepted and supported.
I guess I should believe everything else that pops up. Every other theory that pops up. They are all true.
But it seems like you know something about entropy (if that was you), so not sure why you are trying to argue the big bang then.

Do you want to bitch about anyone saying a theory is a fact? You know how many things we take for granted in everyday science are theories?
Lets just familiarize ourselves with what a scientific theory is"
A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation.[1][2][3] As with most (if not all) forms of scientific knowledge, scientific theories are inductive in nature and aim for predictive power and explanatory capability.

There is no reason to think the universe is infinite.

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There isn't political controversy in this.

17. ### andnowweknowI heard Trump lost

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the big bang doesn't make any logical sense anyway, outside equations.

It still begs the question, what is more confounding...

-that the universe had a beginning

Or

-that it has always been

both are a total mindfuck.

18. ### klnOmegaBannedBanned

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Are you incapable of thinking for yourself? Do you need everyone else to feed you your beliefs and opinions?

If everyone thought like you, how would science ever advance? We would still be stuck believing Apollo pulled the sun because "hurrr well most people believe it so it must be true"

What are you trying to say here? If you know what entropy is, you must adhere to the Big Bang? How does that follow?

You are stating something as a fact, that no one knows is a fact. Thats what we are making fun off. You are 100% sure the big bang happened...no cosmologist is anywhere near that sure. Most cosmologist work with all models interchangeably. When you do new work, you usually ask "how does this fit and modify with the standard cosmology? How does it fit and modify a Baum

19. ### klnOmegaBannedBanned

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Damnit. Move me back the war room. I fucking hate Gayberry Lounge.

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