Is quantum physics too small to interact with gravity?

[AviSchiffmann]

Hi so I don't know too much, but I was watching a video and it talked about how scientists have trouble unifying gravity with quantum physics. So I was wondering, maybe we have to take gravity out of the question because all these super tiny things are just too small for gravity to have an affect?

I don't know much but just a random thought...

[koti]

18 minutes ago, AviSchiffmann said:

Hi so I don't know too much, but I was watching a video and it talked about how scientists have trouble unifying gravity with quantum physics. So I was wondering, maybe we have to take gravity out of the question because all these super tiny things are just too small for gravity to have an affect?

I don't know much but just a random thought...

What if the thing is very tiny but very heavy at the same time?

[Markus Hanke]

27 minutes ago, AviSchiffmann said:

Hi so I don't know too much, but I was watching a video and it talked about how scientists have trouble unifying gravity with quantum physics. So I was wondering, maybe we have to take gravity out of the question because all these super tiny things are just too small for gravity to have an affect?

I don't know much but just a random thought...

You are right that under most normal circumstances, gravity plays no role on very small scales, because the other fundamental forces (weak, strong, and electromagnetism) are very much stronger on those scales by many, many orders of magnitude.

However, there are situations when gravity becomes substantial enough that it can no longer be ignored, not even on small scales - for example in the region behind event horizons of black holes, or at the very earliest moments after the Big Bang. So in order to understand those scenarios, we need to find ways to bring together gravity and quantum physics, which is not at all a trivial task (for mostly technical reasons). This is currently an area of intensive and very active research, and has been for some time.

[geordief]

59 minutes ago, Markus Hanke said:

You are right that under most normal circumstances, gravity plays no role on very small scales, because the other fundamental forces (weak, strong, and electromagnetism) are very much stronger on those scales by many, many orders of magnitude.

However, there are situations when gravity becomes substantial enough that it can no longer be ignored, not even on small scales - for example in the region behind event horizons of black holes, or at the very earliest moments after the Big Bang. So in order to understand those scenarios, we need to find ways to bring together gravity and quantum physics, which is not at all a trivial task (for mostly technical reasons). This is currently an area of intensive and very active research, and has been for some time.

Are there any  promising new  approaches being explored at the present time? Are there fundamental aspects  a  hoped for theory  where it is confidently expected that elements of General Relativity  and elements of Quantum Theories  broadly overlap?

 

Would Fields be one of them? 

 

Should the application of Special Relativity inside the atom be counted as a step along the path to  a theory of Quantum Gravity (didn't Relativity start out as "Special"  and progress to "General"? 

[Markus Hanke]

1 hour ago, geordief said:

Are there any  promising new  approaches being explored at the present time? Are there fundamental aspects  a  hoped for theory  where it is confidently expected that elements of General Relativity  and elements of Quantum Theories  broadly overlap?

There is a substantial number of what I would consider promising approaches, though it is not yet obvious whether a fully self-consistent model of QG is among them - there is always a chance that there isn’t. The trouble is that we have not got the mathematical abilities to fully work out and understand many of these candidate theories, so it is difficult to evaluate their actual value to us. What’s more, we don’t even know what a fully consistent model of QG should look like, and what features it would have.

At present the best candidate models would remain Loop Quantum Gravity, Non-Commutative Geometry, Causal Sets, Causal Dynamical Triangulations, Asymptotically Safe Gravity, and M-Theory. This is not a complete list though.

M-Theory actually goes a step beyond QG, in that it is a candidate for a “theory of everything” that could model not just gravity, but the entire particle zoo through a unification of all fundamental interactions. 

1 hour ago, geordief said:

Would Fields be one of them? 

There is a candidate theory of QG called Group Field Theory. I can’t really comment on it though, since I am largely unfamiliar with this particular model, except in the broadest of terms.

1 hour ago, geordief said:

Should the application of Special Relativity inside the atom be counted as a step along the path to  a theory of Quantum Gravity

Yes, because before you can even begin to worry about gravity on small scales, you need to first understand the other fundamental interactions, which are orders of magnitude stronger. Doing this leads to quantum field theory, which is the unification of quantum mechanics and special relativity.

[geordief]

42 minutes ago, Markus Hanke said:

The trouble is that we have not got the mathematical abilities to fully work out and understand many of these candidate theories,

That is a bit of a surprise to me. You mean these  candidate theories can be developed without mathematical underpinning and then wait for mathematics to catch up?

 

What kind of methods are used when mathematics  can not be used ?

 

Strange that someone as poor at maths (and deductive skills)  as I am should be asking this question.Can maths be seen as the skeleton within the flesh of creative reasoning?                             

[studiot]

48 minutes ago, geordief said:

That is a bit of a surprise to me. You mean these  candidate theories can be developed without mathematical underpinning and then wait for mathematics to catch up?

Yes, of course. That is how Einstein's relativity was born.

But that does not mean anything goes just because someone fancies pink unicorns.

Nor is this to say the Einstein was a mathematical dunce.

 

Proper scientific reasoning hand-in-hand with observation is more important than mathematics in my opinion.

Here is a really superb example

Quote

Swinnerton

In the solid rock itself it was those crystals that began to grow first that were free to take on the proper regular shapes. Those that began later had to be content to fill up the space that was left, so could not assume their proper crystalline form. From what is seen in a piece of granite it is clear that felspar crystallized out before the quartz. Quite often you will find small crystals of mica inside the large crystal of felspar, and they must therefore have been formed first.

 

Watch my hands - no mathematics at all but we have discovered the order of melting points of these minerals.

Edited June 23, 2018 by studiot

[StringJunky]

20 minutes ago, studiot said:

Yes, of course. That is how Einstein's relativity was born.

But that does not mean anything goes just because someone fancies pink unicorns.

Nor is this to say the Einstein was a mathematical dunce.

 

Proper scientific reasoning hand-in-hand with observation is more important than mathematics in my opinion.

Here is a really superb example

 

Watch my hands - no mathematics at all but we have discovered the order of melting points of these minerals.

Maths describes the answer, It is not the source of the answer itself. Apparently, Einstein made that mistake later in life; thinking that the answer was in the maths. One can go too far the  other way from neglecting intuition, imagination etc.

Edited June 23, 2018 by StringJunky

[Markus Hanke]

2 hours ago, geordief said:

You mean these  candidate theories can be developed without mathematical underpinning and then wait for mathematics to catch up?

The problem is akin to having a mathematical formalism, but not being able to extract specific predictions from it, because the mathematical tools are missing to work with that formalism. For example, you can know the Einstein field equations, but if you haven’t got a clue how to go about solving them, then you can’t extract any of the physics. So it’s a matter of developing mathematical tools as you go along, and that takes time - which is why String theory appears to have stagnated of late. Actually there is continuous progress, but it’s mostly very technical stuff, and the progress is slow.

This issue partly persists even with well-studied models. For example, a complete classification of all possible solutions of the Einstein equations is (to the best of my limited knowledge) still an outstanding problem. Another example is QCD (the strong force) - the field equations are so complex that no closed analytical treatment is possible; we largely rely on numerical simulations as well as simplified approximations.

2 hours ago, geordief said:

What kind of methods are used when mathematics  can not be used ?

I don’t think there is an alternative to maths when it comes to QG. Of course, it all starts with ideas and approaches, but then these need to be fleshed out with a proper formalism, or else no one will ever know what these models actually say, in physical terms.

Edited June 23, 2018 by Markus Hanke

[studiot]

2 hours ago, Markus Hanke said:

Of course, it all starts with ideas and approaches, but then these need to be fleshed out with a proper formalism, or else no one will ever know what these models actually say, in physical terms.

I agree but the link between the formalism and what the modle says about physical reality is often not clear to readers.

For example what do the following famous formalisms tell us is happening in Physical reality.

[math]{\nabla ^2}\varphi  = 0[/math]

 

[math]{\left( {\int {fgdx} } \right)^2} \le \left( {\int {{f^2}dx} } \right)\left( {\int {{g^2}dx} } \right)[/math]

 

The latter is, of course one of the foundation statements of the quantum theory.

[Markus Hanke]

The former means that the divergence of the gradient of your function vanishes everywhere, so there are no sources or sinks of any gradient (not field) flow. In physical terms, this means that, if you consider a small region centered around some point, the average value of your function in that region must be equal to the value of your function at that point. If the relationship holds everywhere, then you are dealing with a harmonic function, which is physically often a wave field of some sort.

Your latter example is a particular form of the Cauchy-Schwarz inequality - it physically means that the inner product of f and g can never be larger than either of these taken in isolation. So in other words, a projection is never larger than either of the vectors/states/functions that are involved in the projection. 

Both of the above are just common sense, and really quite simple - but you are absolutely right, actually extracting this information from the formalism is a non-trivial task. And that was precisely my point - we can have models of QG that give us a more or less straightforward mathematical statement, and yet we may be unable to physically interpret it. For example, without the entire theory of differential equations, you could not easily extract any physics out of Laplace’s equation, because you would have no way of solving them.

[geordief]

19 hours ago, studiot said:

 

Proper scientific reasoning hand-in-hand with observation is more important than mathematics in my opinion.

Here is a really superb example

quote from Swinnerton

"In the solid rock itself it was those crystals that began to grow first that were free to take on the proper regular shapes. Those that began later had to be content to fill up the space that was left, so could not assume their proper crystalline form. From what is seen in a piece of granite it is clear that felspar crystallized out before the quartz. Quite often you will find small crystals of mica inside the large crystal of felspar, and they must therefore have been formed first."

 

Watch my hands - no mathematics at all but we have discovered the order of melting points of these minerals.

Another superb example of observation is Temple Grandin (I caught the docu on BBC a few days back..) and her "huge box".  . unbelievable but true

 

https://en.wikipedia.org/wiki/Temple_Grandin

 

Yes observation  really is  a praiseworthy skill and aptitude.  

Edited June 24, 2018 by geordief

[studiot]

5 hours ago, Markus Hanke said:

The former means that the divergence of the gradient of your function vanishes everywhere, so there are no sources or sinks of any gradient (not field) flow. In physical terms, this means that, if you consider a small region centered around some point, the average value of your function in that region must be equal to the value of your function at that point. If the relationship holds everywhere, then you are dealing with a harmonic function, which is physically often a wave field of some sort.

Your latter example is a particular form of the Cauchy-Schwarz inequality - it physically means that the inner product of f and g can never be larger than either of these taken in isolation. So in other words, a projection is never larger than either of the vectors/states/functions that are involved in the projection. 

Both of the above are just common sense, and really quite simple - but you are absolutely right, actually extracting this information from the formalism is a non-trivial task. And that was precisely my point - we can have models of QG that give us a more or less straightforward mathematical statement, and yet we may be unable to physically interpret it. For example, without the entire theory of differential equations, you could not easily extract any physics out of Laplace’s equation, because you would have no way of solving them.

 

You know this and I know this but but does the dog in the doorway know this?

(Have you come across that old saw?)

IOW how do you get from (1) to the difference between electric and magnetic fields or (2) from C-S to Heisenberg?

You need some physical reasoning and observation.

[Markus Hanke]

3 hours ago, studiot said:

You know this and I know this but but does the dog in the doorway know this?

Indeed - that’s pretty much the point I am trying to make.

3 hours ago, studiot said:

You need some physical reasoning and observation.

Yes, I do not deny the importance of physical reasoning. What I am attempting to say is that this will be very difficult in the case of QG, because there is no direct observational data available (just yet), and we also do not know what such a model is even supposed to look like, so physical reasoning is hard. In the case of M-Theory the situation is worse still, because we don’t even have a complete formalism yet, let alone a physical interpretation of it.

[studiot]

6 minutes ago, Markus Hanke said:

In the case of M-Theory the situation is worse still, because we don’t even have a complete formalism yet, let alone a physical interpretation of it.

So strictly in accordance with the rules of ScienceForums they are not theories they are speculations.

Small wonder the dog thinks its a pussy cat.

[Markus Hanke]

7 minutes ago, studiot said:

So strictly in accordance with the rules of ScienceForums they are not theories they are speculations.

Strictly speaking I think one might be able to make that argument. But then the same could be said for any QG model, since technologically speaking we are very far away from being able to experimentally test such models, so even a fully worked out and understood QG model is likely to remain speculation for some time to come.

But it should be pointed out that not all speculations are created equal - some are speculative extensions or generalisations of already established models, while others are not rooted in established physics at all.

[Sensei]

Quote

Is quantum physics too small to interact with gravity?

Maybe you would like to rephrase it to "does quantum physics in lab operate on too large energies to be able to detect so subtle things like gravity?"..

 

Edited June 24, 2018 by Sensei

[Higg’s White Hole]

On 6/23/2018 at 1:54 AM, AviSchiffmann said:

Hi so I don't know too much, but I was watching a video and it talked about how scientists have trouble unifying gravity with quantum physics. So I was wondering, maybe we have to take gravity out of the question because all these super tiny things are just too small for gravity to have an affect?

I don't know much but just a random thought...

The idea that I understand is that space is too small to fit quantum mass. The original curvatures that could be generated by space could only house photons. Space needed to dilate to fit the quantum, but being comprised of the original measure, is still too small to house quantum mass, this nullifying gravity except loop quantum gravity which occurs when space is forced back to 0 overcoming the dilated quantum measure of space.

[beecee]

1 hour ago, Higg’s White Hole said:

 The original curvatures that could be generated by space could only house photons. 

?? Spacetime curvature [that is gravity] is "generated" actually caused by mass/energy. Photons traverse spacetime in geodesic paths.

Quote

Space needed to dilate to fit the quantum, but being comprised of the original measure, is still too small to house quantum mass, this nullifying gravity except loop quantum gravity which occurs when space is forced back to 0 overcoming the dilated quantum measure of space.

https://www.youtube.com/watch?v=4gr77sPBjS4

 

[Strange]

10 hours ago, Higg’s White Hole said:

The idea that I understand is that space is too small to fit quantum mass.

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." Douglas Adams, The Hitchhiker's Guide to the Galaxy

I don't what you mean by space being too small. And what is "quantum mass"?

Quote

The original curvatures that could be generated by space could only house photons. 

What are "the original curvatures"?

And why do you think they could only "house" photons? 

10 hours ago, Higg’s White Hole said:

Space needed to dilate to fit the quantum

What does "to fit the quantum" mean? Quantum of what? And how big is it?

10 hours ago, Higg’s White Hole said:

this nullifying gravity

Really? There is no gravity? Wow.

Please don't post this drivel in the science sections of the forum. 

[swansont]

On 6/23/2018 at 4:54 AM, AviSchiffmann said:

So I was wondering, maybe we have to take gravity out of the question because all these super tiny things are just too small for gravity to have an affect?

I was reminded yesterday that thinking about QM as applying only on small scales is a mistake. QM applies on larger scales, but the "weird" effects tend to cancel out, and we are left with classical behavior.