Using Magnetic Fields to Produce Gravitational Fields

[Nytmare]

http://www.sciencedaily.com/releases/2016/01/160108083918.htm

Wait, what? Anyone here with the appropriate combinations of letters after their name who can go over this in layman's terms for us? Is it just "We've noticed that we can bend light with magnetic fields, so we're going to reeeeeeeeally bend the light with a really powerful magnetic field and see if we accidentally made gravity"?

 

[tomBitonti]

Hi,

Seems pretty unlikely.

You might want to re-post on the AMA forum, on the ask-a-physicist topic.

As far as I'm aware, barring some type of new (and currently unknown) exotic matter, there is no way to create a gravitational field except with mass/energy.

The energy of a magnetic field will have an associated gravitational field, but the field would be too small to be worth considering, except with an extremely intense magnetic field, which I'm thinking we are no-where able to make. I wonder if the very strong field say, around a rotating pulsar, would be strong enough.

Thx!

TomB

 

[Umbran]

As far as I'm aware, barring some type of new (and currently unknown) exotic matter, there is no way to create a gravitational field except with mass/energy.

The energy of a magnetic field will have an associated gravitational field, but the field would be too small to be worth considering, except with an extremely intense magnetic field, which I'm thinking we are no-where able to make.

I haven't seen the math, so I can't comment directly on that.

However, let us be clear about something. It isn't that there's no way to create a gravitational field except with mass/energy. It is that mass/energy has a gravitational field associated with it. ALWAYS. You cannot have mass/energy without there being an associated gravitational field.

So, it isn't a question about whether you can do it. It is a question of how intense a field you can get, and how precise is your gravitational detector.

The real issue I see is that I suspect any field sufficiently strong will start spitting out particles by pair production and shed that energy long before it reaches a level we can detect the associated gravity with current equipment.

Edit: Ah, wait, reading the abstract, ah, I see! He's suggesting using a solenoid, and measuring the gravitational field by looking for red shift in photons that pass through the field. Very interesting.

Edit 2: Ah, now, reading more of the paper - yes, he's using the mass-energy equivalence principle. There's actually no new theory here at all, nothing exotic is going on. In theory, this will work fine. The only questions are the practical ones of "can I build a strong magnetic field" and "are my laser interferometers precise enough to measure the effect".

 

[tomBitonti]

I haven't seen the math, so I can't comment directly on that.

However, let us be clear about something. It isn't that there's no way to create a gravitational field except with mass/energy. It is that mass/energy has a gravitational field associated with it. ALWAYS. You cannot have mass/energy without there being an associated gravitational field.

Doesn't the implication work in both directions? That is, to complete the relationship: You cannot have the field without the presence of mass/energy?

Edit: Ah, wait, reading the abstract, ah, I see! He's suggesting using a solenoid, and measuring the gravitational field by looking for red shift in photons that pass through the field. Very interesting.

Edit 2: Ah, now, reading more of the paper - yes, he's using the mass-energy equivalence principle. There's actually no new theory here at all, nothing exotic is going on. In theory, this will work fine. The only questions are the practical ones of "can I build a strong magnetic field" and "are my laser interferometers precise enough to measure the effect".

One of the pages that describes the idea has:

http://nouvelles.unamur.be/upnews.2016-01-07.3935356861/view (with English text provided by google translate):

In his article, the professor proposes mathematical proof in support, a device that would create weak gravitational fields, but detectable from two superconducting electromagnets several meters in diameter. A device that is based on mature technologies, such as CERN or ITER.

I'm wondering how the field is produced, and why it would be better to create the field in a complicated way (with a magnetic field) rather than by simply adding/removing mass. Could a magnetic field produce a bigger mass/energy density, or somehow create an oscillation or a gradient which would be more useful for creating gravity waves?

But I didn't think that magnetic fields affected photons (http://van.physics.illinois.edu/qa/listing.php?id=2009), so I'm not even understanding how detection would work.

From that link:

Now the disclaimers back on your original question: If your magnetic field is strong enough over a large enough distance, you can have enough energy stored in it to do gravitational lensing, and then refer to the above answer on gravitational lensing. This however is a very difficult way of getting a strong gravitational field. It is much easier just to collect a galaxy’s worth of matter than to collect the equivalent energy in a magnetic field (neither is particularly easy, I admit!)

The second disclaimer is that there is a small expected deviation from linearity of electric and magnetic fields due to quantum mechanics and the ability of electrons to pop out and go away on microscopic time scales. This only becomes noticeable for very very high frequency light colliding with other very very high-frequency light (it wouldn’t be noticeable and may even have exactly zero effect for a static magnetic field and visible light -- I haven’t done any calculations). There are plans to make such a light-light collider, but it requires a many-mile electron accelerator to get the energy of the light high enough.

Thx!
TomB

 

[Umbran]

Doesn't the implication work in both directions? That is, to complete the relationship: You cannot have the field without the presence of mass/energy?

Quite possibly, but that's not really relevant for purposes of this particular topic.

I'm wondering how the field is produced

Well, the deepest of the "how" is probably quantum gravity, which we don't have worked out. "Presence of mass/energy created gravitational field" is sufficient for our purposes.

and why it would be better to create the field in a complicated way (with a magnetic field) rather than by simply adding/removing mass. Could a magnetic field produce a bigger mass/energy density, or somehow create an oscillation or a gradient which would be more useful for creating gravity waves?

Several things:

With normal matter, you have the issue of having to hold it in place, and you can't actually change the amount present very easily ("Hold on, Fred, shut it down! I have to add another grain of sand!"). Also, matter has this annoying tendency to be opaque, as does whatever holds the matter in place, which may make shining a laser through the area difficult.

Meanwhile, with a magnetic field, you get to run a current through some superconducting loops, and some distance away you have a thoroughly transparent region that is still packed with energy/mass in the form of magnetic field. And, by only small changes in the current, you get to play with changes in "mass". Yes, you could even pulse the current to produce changes in mass, and thus waves, but I am not sure that's the actual goal.

But I didn't think that magnetic fields affected photons (http://van.physics.illinois.edu/qa/listing.php?id=2009), so I'm not even understanding how detection would work.

You *want* the magnetic fields to not affect the laser directly - you want the area to be as transparent as possible. But it is actually wave-nature you're looking at, not photons, because we are going to use the same basic concept we use for LIGO or other gravity detectors - interferometry.

Consider - have the current off, shine the laser through, it travels some distance. Turn the current on. That packs a region with energy/mass, and so creates a (small) gravitational field. With that present, you shine the laser, and its path *bends* just slightly, which means it travels a slightly different distance. Compare the path difference with interferometry, and you can detect *very* small differences in path length.

Actually, what you probably do is take a laser beam, and split it. You have two beams travel some distance separately, and recombine them. You tune the apparatus so they're travelling the *exact* same distance (or, some multiple of whole wavelengths, so when they recombine, the waves are in-step, and constructively interfere). Now, on one of the paths, you turn on that magnetic field. The path on that one side bends ever so slightly. When they recombine, the waves will be *slightly* out of synch, and you can see the drop in intensity from destructive interference. Measure that, you have measured the path difference, and thus the strength of the gravitational field.

 

[tomBitonti]

But still, it seems that using simple matter would create much bigger effects. Can a greater mass-energy density really be created with a magnetic field? Or is the finer control sufficient to overcome the lessened size of the fields?

Also, does the summarization misstate the use of magnetic fields in the detector as actual use of magnetic fields to do the detection?

Thx!
TomB

 

[freyar]

But still, it seems that using simple matter would create much bigger effects. Can a greater mass-energy density really be created with a magnetic field? Or is the finer control sufficient to overcome the lessened size of the fields?

The author seems to be after two things in the experimental set up. (1) Testing that the equivalence principle applies to electromagnetic fields. To do that, clearly, you need gravitational effects created by electromagnetic fields. (2) Fine control over gravity. It's just hard to control large amounts of mass that precisely.

I can't say I'm optimistic about the experiment, though, because (despite claims in the article), it looks too hard to do. To get a measurable phase shift, the article says you need to have a light wave bouncing around in the interferometer for 200 days (coherently). I'm skeptical that we can do that. In particular, the detector would basically have to be something as sensitive as a LIGO detector, so I don't see how a passing gravitational wave (created by, say, 2 colliding black holes a few galaxies away) wouldn't constitute an irreducible floor for the background. That means a lot more work. I also don't really expect any big push to do this experiment (though I'm just a theorist and don't always understand the motivations of experimentalists). It just seems that, if you are going to go to the trouble to make a detector like this, there are bigger fish to fry --- like gravitational wave astronomy. The total apparent lack of interest from the scientific community since this paper first appeared in April is also somewhat telling.

The paper does have a nice numerical calculation of the joint solution for a magnetic field, the gravitational effects it produces, and how that gravity in turn affects the magnetic field.

Also, does the summarization misstate the use of magnetic fields in the detector as actual use of magnetic fields to do the detection?

I don't quite follow this question, but I'll happily try to answer it if you can rephrase it.

 

[tomBitonti]

Also, does the summarization misstate the use of magnetic fields in the detector as actual use of magnetic fields to do the detection?

I don't quite follow this question, but I'll happily try to answer it if you can rephrase it.

The science news summary has this text:

Produce and detect gravitational fields at will using magnetic fields, control them for studying them, work with them to produce new technologies -- it sounds daring, but one physicist has proposed just that in a new article. If followed, this proposal could transform physics and shake up Einstein's theory of general relativity.

Bold added by me for emphasis. I'm trying to understand how the magnetic fields are or could be used in the detector.

Thx!
TomB

 

[Umbran]

I think that's just a misstatement.

 

[tomBitonti]

I think that's just a misstatement.

Yeah, that's what I was thinking.

The summary seems quite misleading:

Produce and detect gravitational fields at will using magnetic fields, control them for studying them, work with them to produce new technologies -- it sounds daring, but one physicist has proposed just that in a new article. If followed, this proposal could transform physics and shake up Einstein's theory of general relativity.

Then: "Produce and control gravitational fields using magnetic fields. Confirm the production of gravitational fields from the mass/energy of magnetic fields."

The "transform physics and shake up Einstein's theory" part seems just wrong. This would provide a confirmation of a suspected result. Nice to have, but unless the result is not the expected one, I don't see how any current theory would be shaken.

The implication for new technologies seems overstated. I can see new technology arising from the very high technical requirements of the detection apparatus, but not anything arising from the confirmation result itself.

Thx!

TomB