• Philosophy and Spirituality
    Welcome Guest
    Posting Rules Bluelight Rules
    Threads of Note Socialize
  • P&S Moderators: JackARoe | Cheshire_Kat

Theoretical Physics vs. Quantum Mechanics

Cyc

Bluelighter
Joined
Sep 11, 2000
Messages
11,370
Location
Canada
So we all know that theoretical physics is the idea that general relativity created what is called a "singularity" at the beginning of time. This singularity consisted of strong nuclear force, weak nuclear force, electromagnetism and gravity all condensed into one vacuum.

Quantum mechanics, however, works on the basis of the "uncertainty principle" which states that matter cannot be measured or predicted because the orbit of electrons is random. This debunks the idea of singularity as a mathematical constant.

So how do we reconcile these two to get a concept of a uniform and law-abiding universe?

Thoughts?
 
The flaw in your argument is in assuming that general relativity and quantum mechanics are both correct.

The problem is that it is already known that general relativity and quantum mechanics are inconsistent with each other.... or rather - general relativity cannot be applied in small regions of space.

This is in fact where a large amount of today's theoretical research is headed - trying to find a quantum theory of gravity.

The two big contenders at the moment are quantum loop gravity and string theory (or more correctly, it's more general version M theory).

Hell it's even obvious on the axioms of their formulation: QM assumes that wavefunctions act in space, a background that is unchanging. GR assumes that the background (space itself) is bent...

QM is generally assumed to be the correct formulation, or at least more correct, in that its answers have been tested (in some areas) to 10 or more decimal places, a rediculously accurate figure. GR is near impossible to test, because it only supersedes newtonian gravity in regions of high mass (or high energy)...

Your idea of the uncertainty principle isn't right... The Heisenberg uncertainty principle strictly states that no eigenvalue of a quantum system can be measured at the same time as another with infinite precision.

In laymans terms: you cannot measure the position and momentum of an object with infinite precision. You could measure the position exactly, but then you'd have no idea about the momentum. You could measuer the momentum exactly, but then you'd have no idea about the position.

The actual relation is (delta_x)*(delta_p)>=h/(4*Pi)
where h is planck's constant, and delta_x and delta_p are the uncertainties in the respective positional measurements.
 
I thought we had already agreed that there are no laws in the universe, so much as there are tendencies. Without laws like cause and effect you are left with the scary idea that things happen just because they do. Most mathematical constants are crap anyway. If you want to be an ass about it, you can say that the all time and space is a single event. Time and space, cause and effect, are just convient ways to deal with reality.
 
^^ Whilst laws are always open to invalidation, it's hard to say that something is not a fairly definitive principle when
a) no contradictions to it have ever been observed
and, more importantly for empirical purposes
b) assuming a law (such as a conservation law) allows many testable predictions which we observe.

e.g. assuming conservation of angular momentum correctly (with schrodinger's eqn) predicts the structure of the hydrogen atom, any any other atom for that matter.
 
But hydrogen is what the majority of matter is made up of (followed by helium), so I think that's a valid example.

Proton accellerators (aka atom smashers) have proven that both TP and QM are both on solild ground.
 
All of these physical systems are just approximations that best model the activity of an ultimately non-definable universe, as we see in the uncertainty principle of quantum mechanics. Which model you use depends on your current reference frame. At high speed, relativity is more accurate, at small size quantum mechanics is more accurate. Cause and effect too is just a model of what happens. These models do a very good job of prediction, or else we would have discarded them a long time ago, but they're still only models.

I had an discussion with a friend a while ago about whether things are "really there". Take a coke can. Is it "a coke can"? A collection of atoms? Of subatomic particles? Of compressed energy? Does it change over time? If you crumple it, is it still a coke can? Was it a coke can before it was painted? Before the tab was added? Before it was molded, before it was mined? We can think up physical systems that will model the behavior of different descriptions of the coke can very accurately, but these all depend on an a completely arbitrary definition of what the coke can is. It's computationally easier on the brain to make a quick definition and stick with it, so all of us do it in day to day life, but we have to accept that the truth of the situation cannot be defined and labeled.
 
Kyk said:
Proton accellerators (aka atom smashers) have proven that both TP and QM are both on solild ground.

True - TP and QM *are* on solid ground. But your argument about the singularity does not come from theoretical physics; it comes from an extrapolation of general relativistic results backwards in time.

Singularities are purely a product of GR, and no-one really confesses to know what happens near singularities.

No-one ever tries to apply GR to very small systems :) It simply doesn't work.
 
Molybdenum said:
All of these physical systems are just approximations that best model the activity of an ultimately non-definable universe, as we see in the uncertainty principle of quantum mechanics.

I agree... perhaps I'm giving the wrong impression. SR, QM, GR, TP etc are all extremely good models - they are the best models we have in certain domains.

Some of them have even been combined
Special relativity + Quantum Mechanics = Relativistic QM.
Add a lot of work from theoretical physics and you start looking at things like the Electroweak theory.

But GR is plainly inconsistent with QM on small scales, and so people are searching for a better model...

Ultimately everything is an approximation in physics... but if your model reproduces everything you see, then its a pretty good model. That's generally how models are replaced -- something is found which does not fit within the model, and so alterations/replacements are sought.

It's going to be pretty hard to throw out QM given its wideranging success.... alterations are certainly possible, but the basic axioms and theory are on very solid ground.
 
Molybdenum said:
I had an discussion with a friend a while ago about whether things are "really there". Take a coke can. Is it "a coke can"? A collection of atoms? Of subatomic particles? Of compressed energy? Does it change over time?

There's better ones yet... Schrodinger's cat is a great example.

Apply that to the moon? If no-one looks at the moon, is it still there?

Interestingly enough the "schrodinger's cat" effect (which is related to quantum coherence) has been detected on systems as large as a millimetres across, which is pretty damn large considering that quantum effects manifest on scales some million times smaller... and quantum decoherence rises rapidly as the scale increases.
 
Just to add a couple things to the excellent info VelocideX has provided...

First some of your language isn't quite right, though the basic idea is. 'Theoretical physics' is just physics that isn't related to designing / performing experiments. The two fundamental physical theories we have are 1) General Relativity and 2) the Standard Model of quantum field theory. GR explains gravitation and so the behavior of the universe at very large scales. The Standard Model explains all the other forces and so the behavior of the universe at small scales. (Vanilla quantum mechanics is an approximation to quantum field theory.)

Singularities, also, aren't mathematical constants. Generally speaking, a singularity is a point where important quantities become undefined, typically going off to infinity as it is approached. eg, the function f(x)=1/x has a singularity at x=0 . In GR, a singularity usually means a point where the density of matter goes to infinity, and time for an observer simply ends (or begins.) This happens at the beginning of the universe -- there's no meaningful way to say what's going on at t=0 or 'before.' In a sense, only positive times exist. That's very odd, but there's no immediate reason to think that quantum mechanics couldn't be valid at all positive times, thus not making the situation any weirder.

However, as VelocideX noted, there *are* fundamental incompatibilities between the two theories. To begin with, they're not even written in the same language. GR treats all mass/energy alike, as a continuous distribution on a curved spacetime. QFT uses entirely different concepts, which are more complicated and much harder to explain, and is built on a flat space. Clearly, if you want to know what happens when both gravity and other forces are important, the two must be able to be merged in some way. The most obvious way to do this -- reformulating GR in QFT terms, just like the other forces -- turns out not to work.

The main current ideas are 1) to try and rewrite QFT so it's not built it off a fixed spacetime -- this is loop quantum gravity, or quantum geometry -- or 2) assume QFT is just an large-distance approximation to another, more fundamental, theory which includes gravity treated just the same as the other forces... this is string theory and its variants.

There's a good short history of all this at http://www.arxiv.org/pdf/gr-qc/0006061 , though it likely won't make much sense without a lot of knowledge about quantum gravity to begin with...

GR is near impossible to test, because it only supersedes newtonian gravity in regions of high mass (or high energy)...
Luckily, we can see plenty of astronomical objects that provide plenty of mass. :) So there are a lot of experimental tests that have been done, actually... see http://pup.princeton.edu/sample_chapters/ciufolini/chapter3.pdf and http://www.arxiv.org/pdf/gr-qc/9811036 for (semi-) recent reviews.
True - TP and QM *are* on solid ground. But your argument about the singularity does not come from theoretical physics; it comes from an extrapolation of general relativistic results backwards in time.
You can also prove (in GR) that singularities must exist at the center of black holes, BTW.
 
General Relativity is flawed in itself. It works on the principle of the ststic universe. The universe isn't static. Just thought I'd point that out. General relativity also needs work on the inflation department.

Those are the two most widely used theories, but not the essential fundamentals. I'd like to see more where this topic goes before I join though. I'm not too confident on my total grasp of QFT, but I have been reading on Quantum loop gravity a lot, and have some ideas about it.
 
What does anyone here have to say to Shulgin's theory that the red-shift effect of the observable universe may be caused by all protons in the universe exponentially increasing in speed? Even though the idea can't really be tested, it can (aparrently) explain a lot of the flaws found in GR, etc.

/me shrugs
 
Well, considering the original wave-pattern was mostly UV, I think he's wrong. I haven't actually heard this theory, but I'll look into it. Check out Joao Magueijo's VSL theory. You might find that interesting. He even wrote a book titled "Faster than the Speed of Light". It's not a real in depth technical read, but it describes it in general terms. Believe me I was disappointed when there wasn't any proofs in it. Then I googled and found some. :p
 
Acidfiend said:
Can someone please eplain to me what a singularity is in terms of string theory? I read an article here: http://www.sciencedaily.com/releases/2004/03/040304073931.htm that seems to be related to this.


What they just explained there has been pointed out with QM, and various other theories. BTW singularities don't exsist in string theory. I don't know what they would call them, maybe snags in the space-time fabric? How, did they explain the underlying space, then? Also what about the gamma-radiation that blackholes are said to emmit?

Them betting Hawkins is a joke. From what I have heard from people who attend classes with him, he isn't making much sense anymore. He's doing more blabbering, and drooling these days. Sad, but true. He was smart, but there's better out there.

BTW if that is based off the Science magazine publication, I wouldn't give them the time of day. Nature was the last decent science rag, and even they've been bought out by politics, and useless bureacracy.
 
David said:
Also what about the gamma-radiation that blackholes are said to emmit?

You're referring to Hawking radiation? Hawking's derivation of this is one of the highpoints of 20th century astrophysics... he showed that general relativity derivations of blackholes are consistent with the laws of thermodynamics.....
 
That would be it. It's not just gamma, but for the sake of arguements I only brought up Gamma. String theory is just too out there for me to believe it. It would require something to be the underlining priciple for it to exsist. I would see space-time more as an ocean like the ones we see on Earth. With dark matter, and energy packets flying through space in waves. Hence scalar waves, and the duality of quantum particles.

I'm not sure, yet it's a little theory I'm working on. It makes my head hurt at times when I start thinking about it too hard, then I'll give up for a while. Hours later the answer to the problem will smack like a ton of bricks in the face, and have to hurry up to write it down.:p I haven't had this in a while, so it's bound to smack me any second now.=D
 
The current best contenders for a "theory of everything" that will unify general relativity and quantum physics is superstring theory, maybe followed by M-theory. However, the mathematics behind them are so formidable (and their concepts are so difficult to test) that if it isn't a dead-end, it will probably be decades before we're even close to a solution.
 
Once they find the theory of everything that we know off at the moment chances are a new level of physics will be discovered with it, if it does happen we'll probably be very confused with it. I wonder how many layers of physics there are. Is it a finite amount? Could it possibly be an infinite amount of layers?
 
Top