Quantum Physics vs. Relativity


s_lone
#1
This is for the science buffs... Perhaps some of you can help me understand this issue a little better...

I've been told and read many times that there are some problems when you try to mix Einstein's relativity with quantum physics. At least theoretically. Yet, it seems that both theoretical models give concrete results and that they can both be used, if they are used in the right context. Unless I'm mistaken, I understand that Einstein's relativity theory works well on the macro scale such as when we are dealing with stars and planets but that it doesn't work so well on the micro scale... At that level, you need quantum mechanics to suitably explain what is going on...

My question is:

At what point do both theories really clash together? If both theories can give concrete results, how can we concretely observe the incompatibility of both theories? At what point between the macro and the micro level do we hit a ''theoretical wall'' and how does that apply in the real world?

Perhaps my question isn't clear enough but I'm sure there is enough here to get the ball going...
 
Dexter Sinister
#2
The heart of the issue is that quantum theory takes no account of gravitational interactions, and general relativity takes no account of the quantized nature of things, it's still a classical theory in that sense. Special relativity has been incorporated into quantum theory, but it doesn't deal with gravity either. It's usually not an issue, because at the quantum scale the electromagnetic and nuclear forces are so overwhelmingly stronger than gravity, and at the macro scale things are generally electrically neutral. Where things break down is in the very extreme circumstances of very high energies, very high densities, and very high velocities, like the interior of a black hole, for instance, or the first gazillionth of a second after the Big Bang.
 
GreenFish66
#3
Although Each piece of the puzzle keeps growing, I know. They still join together, to make 1 Big Picture, 1 A Whole..!.(hahahahahahaha.(awhole)hahaha. yeah I laugh at my own jokes....cuz if I don't ,who will.?.)

All theories of everything are uselful for something....

Relativety -quantuum- complexity-chaos all tied together with a bit of string theory ..They all have their own space and time.but are intertwinded into something much larger,,..Depends what your looking for..From the infinite to the infintesimal ...It's all around us and in us...

We all use them all everyday in many ways...

A balanced /sustainable approach is the best way to address any theory..Question /Choices /options /facts/answer. ..What is the question you are trying to answer?..Which theory works best given the situation ?..It's all in the question .If you ask the right question..these theories will all work together to get one Working /tested truth..1 theory of everything?..possible ..Many theories of everything more probable..Quatuum tends to take things apart let them grow on their own.Then take them apart again..Relativity attempts ,mostly successfully, at putting things back together as 1 whole...All ways are necessary and useful in themselves at making 1 big picture for us all to understand..That's the goal anyway ..

Although Each piece of the puzzle keeps growing, I know. They still join together, to make 1 Big Picture, 1 A Whole..!.

So I believe..Each to their own..

Thank-you for this space and your time...

B.Greenfish66
 
s_lone
#4
Quote: Originally Posted by Dexter SinisterView Post

The heart of the issue is that quantum theory takes no account of gravitational interactions, and general relativity takes no account of the quantized nature of things, it's still a classical theory in that sense. Special relativity has been incorporated into quantum theory, but it doesn't deal with gravity either. It's usually not an issue, because at the quantum scale the electromagnetic and nuclear forces are so overwhelmingly stronger than gravity, and at the macro scale things are generally electrically neutral. Where things break down is in the very extreme circumstances of very high energies, very high densities, and very high velocities, like the interior of a black hole, for instance, or the first gazillionth of a second after the Big Bang.

Thanks... And if ''things'' break down in in the conditions you describe, I can understand how it's hard to verify and experiment it directly...

But if you consider the ''normal'' conditions that are right around us in our daily lives, is there a precise tipping point where you need to switch theories when you are dealing with practical applications? Are there any situations where you need to take both into account?
 
GreenFish66
#5
We all might be sitting in a chair..Typing with our hands..Looking with eyes..But I am here ,you are there..How can we be sure ? Because we can agree..Both are necessary..Always.

Over and out there from here..
 
Unforgiven
#6
Doesn't the switch come at the molecular level? Granted I don't understand physics on any level but I thought that Enstien's theory worked fine until you get to atoms and then fails to describe. Which left the two theories, Theory of Relativity and Quantum Theory working but un-unified.
 
Dexter Sinister
#7
I dunno that there's a precise tipping point where you need to switch, generally it's pretty clear from the circumstances which one is appropriate, but Niflmir could give you a better answer, he's doing Ph.D. level work in general relativity. Thinking of designing a worm hole in space-time? I think you need both for that.

Quantum theory's about the interactions of sub-atomic entities, I don't think anybody'd use it when dealing with molecules or atoms except under very special circumstances, they'd more likely use the classical theories of chemistry and physics, they're usually accurate enough.
Last edited by Dexter Sinister; Jun 2nd, 2009 at 09:44 AM..
 
Niflmir
#8
You need both when you want to describe something which is both very massive (compact really) and very small, the big bang is the typical example. Many hope that quantum gravity will also resolve the "problem" with the singularities in black holes.

Neutron stars need both general relativity and quantum mechanics but not necessarily quantum gravity. At least, we don't think so. You need the quantum mechanics to describe the degeneracy pressure keeping the star from collapsing and the general relativity to describe the gravity properly at that compactness.

You can ignore general relativity typically when gravity is negligible or when (v/c) << 1 and quantum mechanics when you don't need to describe things on the particle scale.
 

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