What is the conflict between General theory of relativity and Quantum theory?

[Chalnoth]

This is a point in theoretical physics that really puzzles me. Why assume that the math is wrong when it yields infinity? Just b/c infinity does not occur in nature as we experience it does not make it nonsense as it relates to the TOE. Isn't it likely that by ignoring this conclusion you may be disregarding one of the biggest pieces of the puzzle?

No, it's literally nonsense in that if you put actual infinities into your theory, you can prove silly things like 2=3.

The way this is done in practice is you draw a little circle around the infinity and declare, "Here be dragons!" and never let any of your calculations go there. This is sort of like the prescription in ordinary arithmetic against dividing by zero.

The problem with this is that in reality, you can't do this. That is, with horizons you can sort of kinda hide the behavior of singularities, but you can't hide that behavior from the perspective of the object falling into the singularity. It doesn't seem unreasonable to me to assume that reality must be sensible for all observers.

 

[Nabeshin]

Of course, all scientific theories to date are effective theories. So this wouldn't be a strike against quantum gravity. It would simply mean there is still more to learn about fundamental physics.

I tend to take this view, since it ensures that I (and people like me) will always be employed.

 

[Chalnoth]

I tend to take this view, since it ensures that I (and people like me) will always be employed.

Haha, well, it isn't actually an obstacle. Even if we someday discovered the correct, full description of fundamental physics, then that doesn't mean we would come close to understanding all of its consequences. Hawking was arguing some years back that it isn't actually possible to understand all of the consequences of physics due to Goedel's first incompleteness theorem, so that there will always be more to learn.

 

[sahmgeek]

Well, yes, it is always possible that we will find a reasonably-accurate theory of quantum gravity that still includes singularities. However, that will just be evidence that theory is an effective theory and not a fully accurate one.

Of course, all scientific theories to date are effective theories. So this wouldn't be a strike against quantum gravity. It would simply mean there is still more to learn about fundamental physics.

again, linguistic hangups happening here - Why would a singularity make sense physically? Isn't it, by definition, the very absence of physicality/matter? hence, infinite gravity, etc... To assume that it SHOULD make sense physically is what is nonsensical. no?

also, why do singularities need to be absent from "accurate" theories.

 

[sahmgeek]

The problem with this is that in reality, you can't do this. That is, with horizons you can sort of kinda hide the behavior of singularities, but you can't hide that behavior from the perspective of the object falling into the singularity. It doesn't seem unreasonable to me to assume that reality must be sensible for all observers.

what type of object would be able to observe a singularity?

 

[Chalnoth]

what type of object would be able to observe a singularity?

Anything that falls into the singularity.

 

[sahmgeek]

Anything that falls into the singularity.

??

Singularities = infinite density (most likely in the form of energy, not in the form of matter since their is also infinite gravity, right?)

does energy make observations? what I'm getting at is that i don't think an "observer" of any kind that we are familiar with could exist at a singularity. could it?

 

[Mark M]

certainly, i get that this is perplexing. perhaps that's the point (and it may not be "wrong"). *shrug*

Did you read the rest of my post?

Infinity is a mathematical concept, it doesn't make sense to use it in the real world, it is absurd. You can make 2+2=5, or pretty much anything you want using infinity.

Like I said in my previous post, if the center of a black hole was a singularity, then it would have infinite density, implying infinitesimal size. I something is infinitesimal, then it would have taken an infinite amount of time to get that way. Which is obviously impossible.

 

[Chalnoth]

??

Singularities = infinite density (most likely in the form of energy, not in the form of matter since their is also infinite gravity, right?)

does energy make observations? what I'm getting at is that i don't think an "observer" of any kind that we are familiar with could exist at a singularity. could it?

It's always possible to use a hypothetical point particle as an "observer", usually called a test particle. The behavior of all such test particles should be sensible, no matter their path. Claiming anything else would literally be nonsense.