A What is the biggest problem to be solved in Quantum Physics in 2023?

[ohwilleke]

In terms of problems that could actually be solved in 2023, I think that the most plausible would be for there to be some sort of breakthrough in how to calculate the path integrals that are used to quantify the predictions of quantum mechanics, perhaps in some way to utilizes quantum computing.

In the area of quantum gravity, it would be a long shot, but it isn't inconceivable that experimental evidence of gravitationally induced decoherence could be discovered.

 

[vanhees71]

It looks as if the reactor-neutrino problem is (close to be) resolved:

https://physics.aps.org/articles/v16/s10

 

[Meir Achuz]

I don't understand what you mean. Also after the redefinition of the SI the relation $c=1/\sqrt{\epsilon_0 \mu_0}$ still holds exactly, and $c$ is the value fixed already in 1983 within the SI. What's right is that now $\mu_0$ has to be measured. It's no longer $4 \pi 10^{-7} \text{N}/\text{A}^2$ as in the old SI but has to be measured since not the elementary charged is defined by a fixed value within the new SI.

The best thing about SI units is that you don't have to use them unless you teach elementary physics or want to sell a book. Rather than try to remember muzero, try to remember $\mu_0/4\pi$, which is easier. You just have to know how many nines there. I think the reason they didn't use the parallel wire force to define the ampere, is that they still don't understand electromagnetism.

 

[PeterDonis]

I think the reason they didn't use the parallel wire force to define the ampere, is that they still don't understand electromagnetism.

What are you basing this on?

 

[Meir Achuz]

If something has been $10^{-7}$ for so many years, why change it?
SI shows 'they' don't understand electromagnetism.

 

[vanhees71]

The best thing about SI units is that you don't have to use them unless you teach elementary physics or want to sell a book. Rather than try to remember muzero, try to remember $\mu_0/4\pi$, which is easier. You just have to know how many nines there. I think the reason they didn't use the parallel wire force to define the ampere, is that they still don't understand electromagnetism.

When teaching elementary physics, of course I use Heaviside Lorentz or even natural units :-).

 

[PeterDonis]

If something has been $10^{-7}$ for so many years, why change it?

Because of improvements in measurement technologies, that make it more accurate to fix the values of other constants.

SI shows 'they' don't understand electromagnetism.

No, it shows that you don't understand the rationales underlying the SI system of units.

 

[Meir Achuz]

Because of improvements in measurement technologies, that make it more accurate to fix the values of other constants.No, it shows that you don't understand the rationales underlying the SI system of units.

You are right.

 

[Meir Achuz]

You are right.

The definition of a unit does not have to be the most accurate way to measure it.

 

[Frabjous]

The definition of a unit does not have to be the most accurate way to measure it.

Why wouldn’t you choose the most accurate way?

 

[Meir Achuz]

Then the definition would change as a more accurate way was determined.
The definition of the ampere instead of the coulomb would just change the number for the coulomb as more experimental accuracy were obtained instead of changing $$\mu_0/4\pi##.

 

[PeterDonis]

Then the definition would change as a more accurate way was determined.

Yes, which is what happens with most systems of units, including SI units.

You still have not stated what, exactly, the problem is with this. The fact that you don't appear to like it is not a problem for anyone but you.

 

[Conn_coord]

The SI uses trial and error.
And that's very true!
Fixation, light speeds, electric charge values are direct hits.
Boltzmann's constant tightly binds temperature to energy.

However, it is not correct to fix changing values - this is an error.
But the error is correctable.
Such "constants" early - electric and magnetic, now - Planck , Stefan-Boltzmann "constant".
The accuracy of measuring such "constants" has already reached the desired level.
It is well known that the system of natural units (c, h, e, ... ) is not closed. And it does not close with G, the gravitational constant, (although G is the true constant)
But there is an opportunity to close it.
This solves the basic problem of quantum metrology.

 

[vanhees71]

The definition of a unit does not have to be the most accurate way to measure it.

Why, do you think, did it take so long to redefine the SI? Of course, it's important that the redefinition doesn't change the units more than necessary, and that's why the now fixed values of the fundamental constants (as well as $\Delta \nu_{\text{Cs}}$) are chosen such as to make the new definition of the Ampere and the other basic units as accurately as possible the same as given by the older one.

 

[Demystifier]

How did the discussion of the biggest problems turned into a discussion of units?

 

[Vanadium 50]

How did the discussion of the biggest problems turned into a discussion of units?

This is PF, where we take any opportunity to detour into metrology.

 

[Demystifier]

Finished!
https://arxiv.org/abs/2301.04448

It's now accepted for publication.

 

[Fra]

It's now accepted for publication.

I know you don't have the full answer, but in section 6 you sketch and emergence for 4D diff but a perturbation around a flat metric, like in perturbative string theory? My question is - in your own thinking that is - is your "vision" that you also want to explain the emergence of spacetime dimenstionality (ie. why 4D?) or do you picture this 4D structure as given, and it's just the general metric that is emergence?

/Fredrik

 

[Demystifier]

I know you don't have the full answer, but in section 6 you sketch and emergence for 4D diff but a perturbation around a flat metric, like in perturbative string theory? My question is - in your own thinking that is - is your "vision" that you also want to explain the emergence of spacetime dimenstionality (ie. why 4D?) or do you picture this 4D structure as given, and it's just the general metric that is emergence?

/Fredrik

No, I have no idea how to explain the 4-dimensionality.