It could be possible to transfer data through gravitational waves (2018)
universal-sci.com
universal-sci.com
I learned a ton of math and physics in the process of asking whether you could turn CERN or the superconducting supercollider into a gravitational wave generator, the most interesting being that conventional laboratory proposals for rotating bar gravitational wave generators and high frequency accelerator based gravitational wave generators are both in the end limited by the same quantity, the physical strength of materials. If you try to spin a bar faster than the point where its tip velocity is moving at roughly the speed of sound in the material, the bar will be ripped apart because the centrifugal force exceeds the tensile strength of the material, and if you try to increase the number of electrons or protons too high in the bundle being accelerated in your accelerator, you are similarly ultimately limited by the physical strength of the magnets responsible for bending the path of the particles into a circle.
The other interesting observation is that the rotating bar obviously has a much higher mass (technically quadrature moment) than you can get circulating in an accelerator, but the angular velocity of the accelerator is so much higher and the exponent on the angular velocity term in the gravitational wave strain calculation is so high (fifth power? I forget, it's been many years) that the magnitudes of the strain producable in a laboratory setting by a rotating bar and by an accelerator are actually very close (and both, unfortunately, are too small to be of interest).
When I went to grad school, my explicit interest was to build a tiny detector to look for high frequency gravitational waves on the grounds that if you wanted to communicate over Inter stellar or larger distances high frequency gravity waves were the best choice for avoiding the dispersion, scattering, and noise background that makes the the E/M spectrum a hard place to talk on long distances (essentially a variant on the SETI "watering hole" frequency choice but pushed into a different medium). I never had a design for a generator, but the idea was to build a table-top size Weber bar or laser interferometer tuned for the kind of high frequency waves you'd want to use for a communication system, and see if anybody happened to be talking on those channels.
The series Three Body Problems goes into many similar points; and the solution described there to the problem of material tensile strength is to use a new type of material, where the primary intermolecular force is strong nuclear force rather than our conventional ones. Using this material; one could construct a long bars capable of gravity wave transmission and reception.
I am excitedly optimistic about humanity finding intelligent extrasolar signals on the gravity wave spectrum.
The book takes place in the context of the Cold War, when it was written. But it’s still amazing today, and holds a lot of water.
Questions addressed: how would we know a signal was intelligent? How many ways could we attempt to interpret it? Is it meant to be interpreted? Why would somebody emit such a thing? Where did it come from? What do we do with what we’ve learned?
EDIT: I couldn't find anything published yet. It's still a work in progress last I heard (from a presentation by the group leader last year), but watch this space.
Now on the topic discussed, using gravitational waves for data transfer instantly reminded me of UVB-76. A similar system but with global reach would be extremely useful for a lot of agencies...
I think the word "Mathematicians" here is pretty important. :-) No physicist doubts that gravitational waves can transfer information, but we all doubt that it will ever be practically possible to generate gravitational waves of an amplitude that we can also detect.
For what it's worth, here is the paper that this press release is touting: https://iopscience.iop.org/article/10.1088/1361-6382/aace79
The abstract:
"A definition of an affine-metric space of the plane wave type is given using the analogy with the properties of plane electromagnetic waves in Minkowski space. The action of the Lie derivative on the 40 components of the nonmetricity 1-form in the 4-dimensional affine-metric space leads to the conclusion that the nonmetricity of a plane wave type is determined by five arbitrary functions of delayed time. A theorem is proved that parts of the nonmetricity 1-form irreducible with respect to the Lorentz transformations of the tangent space, such as the Weyl 1-form, the trace 1-form, and the spin 3 1-form, are defined by one arbitrary function each, and the spin 2 1-form is defined by two arbitrary functions. This proves the possibility of transmitting information with the help of nonmetricity waves."
Next: What do you propose is going through the double slit experiment here? The gravitational wave? Matter is transparent to gravitational waves, so it would be difficult to build such a double slit experiment. As another poster here mused, you could probably make some kind of interesting meta-material analogous to a crystal lattice and get some interesting gravitational-wave diffraction pattern. But I'm not sure if this is what you're getting at. The point of the famous double slit experiment for photons is that it shows the dual wave/particle nature of photons (or other elementary particles like electrons). Since we don't have a quantum theory of gravity I suppose it's an open question what the outcome of such an experiment with gravitational waves would be.
In the two black holes example, the gravitational wave oscillates at 50 Hz. Its spatial speed is irrelevant. This means that the distance between the two micro-slits would be modulated at 50 Hz with the micro-amplitude of that gravitational wave.
Let's say the distance between the two slits is L, it's modulated in the L0.9..L1.1 range at 50 Hz, the screen that captures the interference image is at 100L distance, to magnify the pattern 100x. This won't work if the modulation amplitude is L1e-60 or something on that scale, as we can't magnify the image 10^60 times.
That you can detect a modulation on a wave, and thus transfer information, is something of a tautology, the tricky bit is modulating gravity. If you can do that we're in a whole different ball game and sending data is probably the least amazing thing you can do with that capability :-)
It's almost like human nature. If anything can be used to send data, we will send data, no matter how inefficient. We will send an entire ICBM with a thermonuclear warhead to send the rather low-entropy message, "Do as I say, or else."
A similar thing could be said about the prospect of sending messages using neutrinos.
But it is only just now barely possible to detect the loudest gravitational wave signals with extreme difficulty and machines costing on the order of a billion dollars. It will remain impossible for humans to generate gravitational wave signals of a detectable amplitude for the foreseeable future.
Source: PhD in gravitational wave detectors.
In a continuous medium like air, water, or a solid, you could describe a "displacement field" d(x) that tells you how far the piece of material that used to be at position x is displaced from its equilibrium position. This is governed by the equations of physical acoustics, which also have wave-like solutions: sound.
The Riemmann curvature tensor R is a function R(x) of spacetime coordinates x, which tells you the curvature of spacetime at location x. Einstein's equations tell you how R evolves, and it also turns out to have wave-like solutions: gravitational waves.
In radio, it's F (or E and B) that's waving. In gravitational waves, it's R.
What's confusing is that R also tells you "the shape of space," and you need to use it to figure out "where" the coordinate x corresponds to.
No, they are completely independent.
Here's another analogous example. Suppose you have a two-dimensional rubber sheet. You put a coordinate system on it, so any position on the rubber sheet can be identified by coordinates (x, y). You deform the rubber sheet so it has a curvy shape - anything you want.
You can have a tensor R(x,y) that tells you the curvature of the rubber sheet as a function of position (x,y). And a scalar T(x,y) that tells you the temperature of the rubber sheet at (x,y). These are completely independent quantities. Different fields.
I'm trying to look at R and F from the signal processing point of view: if we apply Fourier transform to both, we'd see that R is described by low frequency band (planetary scale distortions), while F would be ideally described by a high frequency band.
https://en.wikipedia.org/wiki/Einstein_ring#:~:text=An%20Ein....
It's possible that you could observe a kind of "shimmer" in the position of background stars as a gravitational wave passes between you and them. In fact there is an attempt to detect gravitational waves this way through pulsar timing:
I get that it's an analogy, but I don't think they would be completely independent quantities here. There is likely going to be some correlation with temperature and curvature of the rubber sheet. It would likely pale in comparison to almost everything else though, but on the topic of discussion that might be a large enough correlation.
Also, don't high energy photons curve spacetime?
Yeah, that's a failure of my analogy. Deforming a rubber sheet does create heat, but deforming spacetime does not create light.
[0] https://en.wikipedia.org/wiki/CERN_Neutrinos_to_Gran_Sasso
Metamaterials with special properties under the gravitational interaction would break this. On the other hand, violations of the Equivalence Principle could point into ways of achieving it.
Flying 100s of huge dudes across the country for a football game isn't a particular efficient use of energy, neither is a Quidditch game with blackholes, all of galaxy tunes in with their gravity wave receivers for the games.
This legit made me laugh. Thanks for this.
Yes, only scored thirty points too.
In a distant future, just before the human started the largest, continent-scale particle accelerator (capable of reaching 10^20 GeV) to collect the final data for the Theory of Everything (ToE), an alien agent Risk Eliminator intervened at the last second and dismantled the accelerator, transforming it into a bunch of trees and grass. The alien told humans that the experimental verification of Theory of Everything was extremely dangerous - This was the experiment that triggered the Vacuum Decay [0] event and destroyed all galaxies in the previous universe. Despite the existential risk that was clearly known prior to the experiment, all civilizations in that universe believed discovering ToE was the ultimate peruse of intelligent life (evolution took a different path), it was allowed to proceed and destroyed the universe. As their brain was the ultimate supercomputer, there were speculations that that civilization found the ToE in the last microsecond before destruction, it was unlikely.
Nevertheless, the experiment was designed to transfer data via powerful gravitational waves as a one-way broadcast, which preserved the history of their existence and the experiment. Being the first scientific civilization of the current universe, the Risk Eliminator's world received the gravitational waves from the previous universe before it was dampened out to undecodable level, successfully reconstructed the data and derived the ToE. Since then, their civilization was known as the Risk Eliminator, and their goal was to silently monitor all intelligent lives, and to destroy all ToE experiments when necessary - evolution took a different path, unlike the previous world, not everyone valued the ToE, such as experiment would be unjust to other civilizations.
The human civilization, or any other civilization, was also forbidden to learn the ToE. First there was the Star Trek-style principle that forbids the transfer of any technical knowledge from a civilization to another, which was well understood. But it's still forbidden even when said civilization already had the capability to derive the ToE experiment via experiment due to practical reasons - it was too risky. The practical applications of ToE would allow a civilization to manipulate an even higher energy level - the energy level reachable by a pre-ToE civilization was already deadly. Also, ToE showed the existence of parallel universes, and that the ToE was only a limited model within an individual universe. The curiosity of the intelligent lives may lead them to start researching super-ToE in experiments with even higher energy level, and this could destroy not one, but multiple universes, which was unacceptable.
Finally, the human physicists and the Risk Eliminator made a deal - similar to how the civilizations in the previous universe may have found the ToE in the last microsecond, the human physicists who saw ToE as the lifetime goal could be allowed to learn it in a lecture, but after they've understood the lecture, they would be killed in a giant plasma fireball. Many prominent physicists agreed. After it was on the news, other researchers, such as some mathematicians who wanted to know the proof of the Goldbach's conjecture, or paleontologists who wished the learn the true reason that caused dinosaur to go extinct, also joined the party.
The last physicists who went to the lecture was Stephen Hawking.
"What is the purpose of the universe?"
"How the heck should I know? You are allowed to leave, Professor."
- Completely bypass any EM shielding / faraday cages designed to stop spies / bugs from transmitting information out of secure facilities
- Transmit information out of underground facilities or caves deep in Afghanistan without worrying about RF attenuation. Indeed, communicate anywhere in the world (or under the sea) without worrying about RF attenuation.
Bypassing the limitations of sending information by RF would be hugely advantageous for the military and intelligence services. The resources of the military industrial complex are staggering. What is the state of the art in unclassified technology regarding generating these waves and modulating them? What would be required to make such transmitters/receivers practical? A breakthrough in materials / fabrication technology? It sounds like the theory is solid, and it's a now an applied science problem?
Theoretically it's very interesting, however.
We can now generate radio waves in a pocket-sized device, without involving celestial objects.
We only just recently managed to detect gravity waves at all, and it took several kilometers of vacuum tubes to do it.
There’s a lot of room for discovery and miniaturization left.
The main problem is how weak gravity is, two electrons have a greater influence on each others movement than two 1 kilogram objects at the same distance has. So unless we figure out a way to decouple gravity from mass we will never solve this problem, and doing that isn't possible with the theoretical physics we have today.
Sure it's theoretically possible, but it doesn't seem very likely any time soon.
As I said in my post you replied to:
> there's going to have to be some significant developments to make this practical.
https://en.wikipedia.org/wiki/The_Hole_Man: "In this story, a team of explorers and scientists on Mars encounter an alien base, in which there is a still-functional communication device. One scientist believes that at the center of the device is a tiny black hole.."
(Niven didn't know yet about Hawking radiation discovered next year..)