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 RonaldFuckingPaul
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 What exactly is a "Theory of Everything"? 
#15965146 - 03/18/12 11:39 PM (1 year, 2 months ago) |
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I've heard that some of the contenders include string theory, M theory, and quantum loop gravity. Enlighten me.
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 DieCommie
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Its a sexy catch phrase that drums up public support for research in certain branches in quantum field theory (QFT) and general relativity(GR). Its a misnomer for sure, no hypothetical theory really purports to describe everything.
The assumption is that all phenomenon are reducible to basic constituents and the theories that govern them, namely QFT and GR then do by extension somehow describe 'everything'. The attempt is to unify these two different field theories (GR is a field theory too) into a Unified Field Theory (a much more appropriate name). The theories you mention are hypothetical theories that are current attempts at being a Unified Field Theory.
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RonaldFuckingPaul
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Re: What exactly is a "Theory of Everything"? [Re: DieCommie]
#15965211 - 03/18/12 11:58 PM (1 year, 2 months ago) |
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Quote:
DieCommie said:
Its a sexy catch phrase that drums up public support for research in certain branches in quantum field theory (QFT) and general relativity(GR). Its a misnomer for sure, no hypothetical theory really purports to describe everything.
The assumption is that all phenomenon are reducible to basic constituents and the theories that govern them, namely QFT and GR then do by extension somehow describe 'everything'. The attempt is to unify these two different field theories (GR is a field theory too) into a Unified Field Theory (a much more appropriate name). The theories you mention are hypothetical theories that are current attempts at being a Unified Field Theory.
So basically the goal is to unify quantum mechanics and general relativity?
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DieCommie
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Yes. And getting physical constants to fall out of the theory rather than have to be experimentally observed would be a bonus too.
(Note that quantum mechanics already is unified with relativity. Its gravity that is the problem, and gravity is what distinguishes general relativity from special relativity.)
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RonaldFuckingPaul
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Re: What exactly is a "Theory of Everything"? [Re: DieCommie]
#15965278 - 03/19/12 12:15 AM (1 year, 2 months ago) |
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Quote:
DieCommie said:
Yes. And getting physical constants to fall out of the theory rather than have to be experimentally observed would be a bonus too.
(Note that quantum mechanics already is unified with relativity. Its gravity that is the problem, and gravity is what distinguishes general relativity from special relativity.)
Ok. Why does gravity fall apart when shit goes subatomic?
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DieCommie
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Thats a good question. Gravity works in the subatomic world just fine. Its quantum mechanics that gravity is incompatible with. Though the subatomic world and the quantum world are similar they are not synonymous. Quantum theories manifests in macroscopic objects too.
Gravity doesnt fall apart when you go subatomic, it becomes negligible and unobservable. Because gravity is so weak, there is no problem describing something like a proton-proton interaction without it. So QFT is able to describe quite a lot without considering gravity at all. But when things get massive that is when gravity starts to become a relevant player. At this point the quantum theories start to break down in their ability to describe and predict. Things like superfluids and chemistry are mostly just quantum mechanical and dont need gravity to be described. Things, things like classical and celestial mechanics are mostly gravitational and dont need quantum theories to describe. This is why black holes are interesting, they are a phenomenon that is distinctly quantum mechanical and gravitational in nature. White dwarfs are also very much described by both quantum mechanical and gravitational theories.
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RonaldFuckingPaul
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Re: What exactly is a "Theory of Everything"? [Re: DieCommie]
#15965358 - 03/19/12 12:36 AM (1 year, 2 months ago) |
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Quote:
DieCommie said:
Thats a good question. Gravity works in the subatomic world just fine. Its quantum mechanics that gravity is incompatible with. Though the subatomic world and the quantum world are similar they are not synonymous. Quantum theories manifests in macroscopic objects too.
Gravity doesnt fall apart when you go subatomic, it becomes negligible and unobservable. Because gravity is so weak, there is no problem describing something like a proton-proton interaction without it. So QFT is able to describe quite a lot without considering gravity at all. But when things get massive that is when gravity starts to become a relevant player. At this point the quantum theories start to break down in their ability to describe and predict. Things like superfluids and chemistry are mostly just quantum mechanical and dont need gravity to be described. Things, things like classical and celestial mechanics are mostly gravitational and dont need quantum theories to describe. This is why black holes are interesting, they are a phenomenon that is distinctly quantum mechanical and gravitational in nature. White dwarfs are also very much described by both quantum mechanical and gravitational theories.
Black holes are really intriguing. How does a star become a candidate to become a black hole? I remember hearing somewhere that it needs to be at least 30-40 times bigger than our sun to become a black hole.
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Pacmanpth
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The mass requirement depends on the density. Low mass black holes are possible, as are high mass stars that just go supernova.
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johnm214
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Re: What exactly is a "Theory of Everything"? [Re: Pacmanpth]
#15966660 - 03/19/12 11:54 AM (1 year, 2 months ago) |
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Quote:
reeferaddict69 said:
Black holes are really intriguing. How does a star become a candidate to become a black hole? I remember hearing somewhere that it needs to be at least 30-40 times bigger than our sun to become a black hole.
These figures refer to the amount of mass needed to generate a sufficient force to create the black hole. A black hole can be of any mass in theory, but the relevant force compressing the items is gravity, and hence you need a large enough mass to generate sufficient force.
I think the limiting factor is the degeneracy pressure of the nucleons, at least that's what's thought to 'support' neutron stars and other very dense objects. Its kinda mind boggling to compare this level of compression to the distances between adjacent nuclei in even a solid block of iron.
Blackholes without a source of additional mass are thought to loss mass over time, so eventually you'll get very small black holes.
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Pacmanpth said:
The mass requirement depends on the density.
Why? A less dense object will eventually become a more dense object as it compresses under its own weight.
Quote:
Low mass black holes are possible, as are high mass stars that just go supernova.
A supernova isn't incompatible with a blackhole.
As for low mass blackholes, I don't see how these could form except through radiative losses of mass from a larger black hole over time.
A large black hole will actually be quite non-dense (at least if you define its volume as that enclosed by the event horizon- I don't know of another sensible definition of a black hole's volume). Similarly, the gravitational field of stars are felt far beyond the borders of its body.
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Pacmanpth
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Re: What exactly is a "Theory of Everything"? [Re: johnm214]
#15967719 - 03/19/12 04:57 PM (1 year, 2 months ago) |
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Quote:
johnm214 said:
Its kinda mind boggling to compare this level of compression to the distances between adjacent nuclei in even a solid block of iron.
Yep, neutron star density is roughly equivalent of all people on Earth compressed down to the size of a sugar cube...crazy stuff.
Quote:
Why? A less dense object will eventually become a more dense object as it compresses under its own weight.
Gravity is a function of distance, density absolutely matters. Spread out the mass over enough volume, and you can have a very massive star with a compression force that isn't high enough to cause a collapse to singularity.
Quote:
A supernova isn't incompatible with a blackhole.
I said "just go supernova", meaning a supernova that doesn't result in a black hole. The point was that high mass stars can result in non-black hole phenomonon, and low mass stars can result in black holes, so it's not just a set mass limit.
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DieCommie
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Quote:
reeferaddict69 said:How does a star become a candidate to become a black hole? I remember hearing somewhere that it needs to be at least 30-40 times bigger than our sun to become a black hole.
Like has been mentioned above, mass density is what makes a black hole. If you have a high enough mass in a small enough volume you get a black hole with a singularity, an event horizon and so on.
http://en.wikipedia.org/wiki/Schwarzschild_radius
With the Schawarzschild radius you can calculate how small a chunk of mass has to be in order to form a black hole.
The Schwarzschild radius of an object is proportional to the mass. Accordingly, the Sun has a Schwarzschild radius of approximately 3.0 km (1.9 mi) while the Earth's is only about 9.0 mm, the size of a peanut. The observable universe's mass has Schwarzschild radius of approximately 10 billion light years.
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Luddite
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venetianblinds
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Re: What exactly is a "Theory of Everything"? [Re: DieCommie]
#15974555 - 03/21/12 01:41 AM (1 year, 2 months ago) |
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Quote:
DieCommie said:
Yes. And getting physical constants to fall out of the theory rather than have to be experimentally observed would be a bonus too.
(Note that quantum mechanics already is unified with relativity. Its gravity that is the problem, and gravity is what distinguishes general relativity from special relativity.)
what do you think about the graviton idea?
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DieCommie
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Re: What exactly is a "Theory of Everything"? [Re: venetianblinds]
#15974606 - 03/21/12 02:02 AM (1 year, 2 months ago) |
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Ha, I think whatever the experts think. 
Seriously though, from what I know I would expect it exists. In quantum field theory all particles have an associated field and all fields have an associated particle. The particle is a quanta of field excitation. Its a matter of taste whether you consider the particle fundamental and the field as a consequence, or if you consider the field fundamental and the particles as as consequence.
In either case, the field and the particle necessarily exist together. There is a gravitational field, we can obviously detect that. If the gravitational field fundamentally acts in a quantum mechanical way then it will have a quantization known as the graviton. Most attempts at a Unified Field Theory do quantize the gravitational field, since quantizing has been so damn successful at just about everything else.
Otherwise, it is possible that a Unified Field Theory will not quantize the gravitational field. Hell, it possible that the Unified Theory wont even be a field theory. But that is highly unlikely and would be very difficult to mesh with all of our current observational data.
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venetianblinds
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Re: What exactly is a "Theory of Everything"? [Re: DieCommie]
#15974648 - 03/21/12 02:14 AM (1 year, 2 months ago) |
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man....i got a hold of the feynman lectures
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Style is the answer to everything.
A fresh way to approach a dull or dangerous thing
To do a dull thing with style is preferable to doing a dangerous thing without it
To do a dangerous thing with style is what I call art. ~Bukowski
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DieCommie
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Re: What exactly is a "Theory of Everything"? [Re: venetianblinds]
#15976737 - 03/21/12 04:33 PM (1 year, 2 months ago) |
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Cool! I bet there are parts that are pretty confusing. But I hope you have some some illuminating chapters in it. I sure did.
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