Effects of magnetism on spacetime curvature, and implications

[jaketodd]

Quotes from Cosmic magnetism, curvature and the expansion dynamics:

"Most interestingly, the coupling between magnetism and geometry implies that even weak fields have a significant impact if the curvature contribution is strong."

"The energy scales involved vary from ∼ 100 MeV at the QCD phase transition, to ∼ 100 GeV in the case of electro-weak (EW) physics and closer to the Planck energy scale for inflation or string cosmology."

The LHC does 13 TeV.

"The tension of the field lines means that the magneto-curvature coupling tends to accelerate positively curved regions..."

A quote from A positively curved visualization of gravity?:

"If one imagines a basketball pressed against the rubber sheet, the portion of the sheet in contact with the ball would be positively curved, but the rest would (as before) be negatively curved, one assumes."

So, accelerating positive curvature, as I understand it, would be like amplifying gravity.

Could this phenomenon ever be used for traveling through space? Or, am I completely misunderstanding this whole topic?

An object accelerating in positive curvature continues to accelerate, as long as the curvature is there. Therefore, there would be no limit to the speed achievable. Reminds me of The warp drive: hyper-fast travel within general relativity. However, in that example, the spacetime, which the spaceship is in, is flat.

Thanks!

 

[PeterDonis]

accelerating positive curvature, as I understand it, would be like amplifying gravity.

Not really, no.

Could this phenomenon ever be used for traveling through space?

No. The paper you linked to, as you will note, says no such thing. It talks about the effects of cosmic magnetic fields on the expansion of the universe. I am skeptical of the claimed magnitude of the effects, but that will be a matter for the cosmology community to work out as it evaluates the paper.

am I completely misunderstanding this whole topic?

Yes.

The "positive curvature" in the PF thread you linked to is spatial curvature, not spacetime curvature. The paper you linked to, OTOH, is talking about the effect of magnetic fields on spacetime curvature. Those are very different things.

 

[jaketodd]

No. The paper you linked to, as you will note, says no such thing. It talks about the effects of cosmic magnetic fields on the expansion of the universe.

If magnetic fields, currently attainable by humans, are much stronger than the ones required for impacting spacetime geometry affecting the expansion of the universe, then why can't we influence much more localized spacetime geometry with magnetism? Thanks

 

[PeterDonis]

If magnetic fields, currently attainable by humans, are much stronger than the ones required for impacting spacetime geometry affecting the expansion of the universe

They aren't. Humans can't create magnetic fields throughout the entire universe, which is what the paper you referenced is discussing. We can only create magnetic fields in an extremely tiny localized region.

why can't we influence much more localized spacetime geometry with magnetism?

Because magnetic fields confined to an extremely tiny localized region are not at all the same thing as magnetic fields throughout the entire universe.

 

[PeterDonis]

The LHC does 13 TeV.

That doesn't mean the LHC creates magnetic fields of that strength. Nor does it mean the LHC creates any significant spacetime curvature. 13 TeV over a large region, say a few billion light-years in size, and lasting for a long time, say a few billion years, would do so; but 13 TeV confined to the LHC's central chamber and lasting for a miniscule fraction of a second, not so much. And even that ignores the fact that the energy the LHC uses does not appear from nowhere; it is already there, because stress-energy is locally conserved. So whatever spacetime curvature you think the LHC is "creating", it isn't--it's already there.

 

[jaketodd]

Because magnetic fields confined to an extremely tiny localized region are not at all the same thing as magnetic fields throughout the entire universe.

But the fabric of the universe is expanding even in tiny localized regions, right, i.e. dark energy? And even without dark energy, isn't the expanding universe also expanding in more localized regions, just not as uniformly as the universe as a whole? (Because all regions are expanding, perhaps from the locus of the universe.) Are you saying dark energy can do it but not magnetism? So why can't we use magnetism to influence spacetime curvature, and maybe expansion in tiny localized regions? What differentiates magnetic fields encompassing the whole universe, from stronger ones that are more localized? And why do the weaker ones fill the whole universe, while stronger ones only affect a tiny localized region?

That doesn't mean the LHC creates magnetic fields of that strength.

Well what is the strength please? Is eV the wrong unit? I tried converting from eV to Tesla, but couldn't figure it out. Is Tesla the correct unit then? Thanks!

 

[PeterDonis]

the fabric of the universe is expanding even in tiny localized regions, right, i.e. dark energy?

Dark energy is present everywhere, at least according to our best current models.

even without dark energy, isn't the expanding universe also expanding in more localized regions, just not as uniformly as the universe as a whole?

No. In the absence of dark energy, the FRW spacetime model is only an approximation valid on large scales, using the average density of matter on those scales. It does not scale down to localized regions, and in particular you can't say that localized regions are expanding. The model is simply not applicable on those scales.

Are you saying dark energy can do it but not magnetism?

I am saying that magnetism created by humans in an extremely tiny localized region is not going to affect the dynamics of the entire universe. Neither would dark energy if it only existed in an extremely tiny localized region. And since the paper you referenced is about the effect of magnetism throughout the entire universe on the dynamics of the entire universe, the kinds of speculations you are making about magnetism in tiny localized regions are simply not supported by the paper you referenced. So unless you have another reference, you are engaging in personal speculation and that is off limits here.

Well what is the strength please?

I don't know what magnetic field strength would correspond to the energies that the LHC creates; there might not even be one since magnetic field strength is not the same thing as energy. What I do know is that the question is irrelevant because (a) the LHC is not creating magnetic fields, and (b) the paper you referenced isn't talking about localized effects anyway, as I said above.

 

[jaketodd]

Ok, sorry.

 

[PeterDonis]

This thread is now closed.