
Mathematicians confirm the possibility of data transfer via gravitational waves - craftyguy
https://phys.org/news/2018-10-mathematicians-possibility-gravitational.html
======
pdonis
"The discovery could lead to a new means of data transfer in space, e.g.,
between space stations."

Sure, we'll be building space stations with gravitational wave transmitters as
soon as we can figure out how to wiggle stars and planets in a controlled
fashion to produce them. That should happen Real Soon Now.

~~~
0xFFFE
C'mon, we can already transmit data across different dimensions using a wrist
watch & morse code. Yeah, bandwidth isn't that great but hey, we could use a
wall clock.

~~~
devgutt
I know you are joking, but transmit information through dimensions using
gravity is one interesting conjecture why gravitational force is so much
weaker than the other forces. It leaks through dimensions. And maybe this type
of communication will be necessary when we have to leave this dimension to
hyperspace because of the entropy [1].

[1]
[http://www.multivax.com/last_question.html](http://www.multivax.com/last_question.html)

~~~
Twisol
For what it’s worth, evidence has come out (explained well by this PBS Space
Time episode [1]) that makes the “gravity propagates over more than three
spatial dimensions” theory a bit less likely.

[1] [https://youtu.be/3HYw6vPR9qU](https://youtu.be/3HYw6vPR9qU)

~~~
devgutt
Interesting video, so it is possible that there is no leak after all, but I
think this does not prove that there are no extra dimensions, as the video
tries to portrait.

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pdonis
From the title of the actual paper:

"gravitational waves of nonmetricity"

It looks like these "gravitational waves" aren't the kind that LIGO has been
detecting, but a hypothetical kind in a hypothetical theory of gravity that is
not the same as General Relativity (there are no "gravitational waves of
nonmetricity" in GR). So for this to be even possible in principle this
hypothetical theory of gravity would have to turn out to be correct (and we
have no evidence to suggest that GR is wrong and some other theory of gravity
is correct).

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eximius
This doesn't seem surprising or particularly exciting. It still propogates at
the speed of light and it is hard to produce/detect. The benefit is... Stuff
can be in the way?

~~~
robkop
Not a scientist in this field at all but could it possibly have less
interference from mediums such as the atmosphere? Hence less signal loss over
transmission?

~~~
pizza
imo it seems like data transfer would be difficult to use gravitational waves
for. LIGO had to measure very tiny compressions occurring due to very very big
things happening faraway in the universe (though I guess being distant isn't a
prereq):

> On January 4th, 2017, LIGO detected two black holes merging into one. One of
> the black holes was 32 times the mass of the Sun (32 M⊙, where M denotes
> mass and ⊙ is a symbol for the Sun) while the other was 19 times the mass of
> the Sun. When they merged, they created a black hole 49 times the mass of
> the Sun. The coalescence instantly converted 2 solar masses of black hole
> mass into the energy that rattled spacetime enough to generate the
> gravitational waves we detected almost 3 billion years after it occurred.
> (Caltech/MIT/LIGO Lab)

> Despite the stupendous energy released by colliding black holes, detecting
> gravitational waves is excessively difficult since the effects they have on
> LIGO’s instruments are incomprehensibly small. This latest wave caused the
> spacetime occupied by LIGO’s arms to stretch and shrink by
> 0.000,000,000,000,000,001 (or 1×10-18) meters (a.k.a. an “attometer”).
> That’s 1000 times smaller than a proton!

[0]
[https://www.ligo.caltech.edu/news/ligo20170601](https://www.ligo.caltech.edu/news/ligo20170601)

~~~
ThePhysicist
It surely is science fiction today but from a physics point of view there's
nothing that would make it impossible. So as a physicist I'd say it's merely
an engineering problem ;)

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tempodox
Any wave that can be modulated and detected lends itself to data transfer, in
principle. The question would be how practical it is.

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YaxelPerez
Is it possible that alien civilizations are using gravitational waves to
communicate? Maybe that's why we've literally had "radio silence" so far.

~~~
rmbeard
Exactly what I was thinking, given we are beginning to go dark (in terms of
radio transmission) as well, perhaps SETI are looking at the wrong type of
information transmission to detect our neighbours. A hypothetical alien
civilization could be using an entirely different type of technology to
transmit information to what we have previously assumed, maybe gravity waves
maybe something else, that we haven't even thought of yet.

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juancampa
If you like hard sci-fi, the amazing trilogy by Liu Cixin The Three Body
Problem uses gravitational wave communication as an important part of the
plot.

~~~
pq0ak2nnd
Long membrane communication.

~~~
juancampa
Such a great chapter. It amazes me how the author can take a huge step back
and get into the mind of this curious character

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datenwolf
Not to sound condescending, but…

You can transmit data by modulating in on top of something that propagates
through space? Well, big deal, who'd thought? /s

In all seriousness, the big problem is, how to create gravitational waves in a
controlled manner in the first place. Because the fact remains, that gravity
is, by several orders of magnitude, the weakest force in our universe and it
takes stooopid amounts of energy (and I means that in an all-encompassing way,
referring to anything that goes into the metric tensor) to create an even
noticeable ripple in spacetime. If we break down spectrally, its easiest to
detect stuff close to DC, I mean, people did it 200 years ago, so to speak,
but only over short distances, and really long integration times
([https://en.wikipedia.org/wiki/Cavendish_experiment](https://en.wikipedia.org/wiki/Cavendish_experiment)).

But anything meaningful for data transmission would require to operate at
significant high frequencies. It's hard enough to wiggle around some
"condensed energy", i.e. mass in the milligram scale at high frequencies,
although in the lasers I build, the end facets of the optical filter are
thrown around with accelerations on the order of 10e6 g-ees, at ~500kHz, but
the gravitational waves created by that wouldn't register at LIGO even if
several thousand of these, running in phase were placed right next to the test
masses.

To make any sensible use of gravitational waves, we'd need to invent some form
of gravitational …aser (light: laser / microwaves: maser), i.e. a gwaser.
Gravitational Wave Amplification by Stimulated Emission of Radiation. Okay, I
admit it, this is one of these gedankenexperiments I play through in my head
from time to time, trying to come up with some technological setup, that could
do it. If I had to make a bet, I'd say whatever it'd be, it'd be similar to a
free electron laser.

But it's foolish to even go further than rough speculation, what components it
possibly may involve, because to really make headway in that direction, we'd
need a workable quantum theory of gravity. And last time I've checked, that's
still an open problem.

On the uphand, should we ever figure out, if one can, and if so how to build a
gwaser, this would open up possibilities far beyond new modes of
communication. I'm talking propulsion that uses gravitational radiation as
"reaction mass" (that'd be a no brainer, since gravitational waves to carry
momentum, that's why the orbits of binary black hole systems decay in the
first place). But maybe even stuff that's really outlandish science fiction,
maybe even not causality breaking (not all timelike curves do violate
causaility; go ahead, draw a few Minkowsky diagrams, to see what I mean) FTL
travel.

And given that, I'd put this mathematical result into the same category of
applicability as the Alcubierre metric: A nice consequence of mathematical
rigor, but without further understanding of fundamental physics of little
practical interest, so far.

~~~
kopo
What does "close to DC" mean?

And "end facets of the optical filter"? What is being thrown around?

~~~
xelxebar
"close to DC"

I assume he's meaphorically using the term "direct current", so the low
frequency stuff. As far as I know, LIGO effectively bandpasses gravitational
waves in the range 7 to 30 Hz, or so.

Calling the Cavendish experiment a measure of gravitational waves, though, is
sorta like saying Newton discovered an early theory of relativity. Not wrong,
in the most pedantic sense, but definitely a bit disingenuous.

I'm not quite sure about the laser facets comment, though.

~~~
datenwolf
> Calling the Cavendish experiment a measure of gravitational waves, though,
> is sorta like saying Newton discovered an early theory of relativity. Not
> wrong, in the most pedantic sense, but definitely a bit disingenuous.

I didn't see the need for sarcasm tags. But then again, if you're honest about
it LIGO is not that much different in _basic principle_ from the Cavendish
experiment (measure the displacement of test masses), only that the
sensitivity of the displacement detector is a lot of orders of magnitude
higher.

And remember that a core step in the Cavendish experiment is to "flip" around
the position of the big masses, so there's some kind of gravitational
transient pulse event, which, if you're honest about translates into a very
broadband spectrum, when compared to the integration time of the experiment.

~~~
xelxebar
First off, thanks for engaging in a bit of debate. I came off a bit needly
when I was trying to allude to a technical point.

I'm guessing that we're talking about different things. If you think of
gravitational waves as any non-zero Fourier transform of some gravitational
potential, then you and I agree, but that's not what we typically mean by
"gravitational waves" which are, formally, metrics admitting a covariantly
null vector field.

One reason for the distinction is that in a GR analysis of the 2-body problem,
the radial potential energy contains an extra term not in a Newtonian
analysis. This is interpreted as energy carried away by gravitational
radiation. Even in a classical case, an external observer witnesses a periodic
gravitational potential, but only in GR do the waves carry energy and cause
Mercury to precess.

The error bars on the early Cavendish experiments were way bigger than any GR
correction to Newtonian gravity. As such, we can safely analyze it within the
realm of Newtonian mechanics which only admits DC offset "gravitational
waves". That was the intent of my original comment.

Actually, as far as I understand it, the Cavendish experiment is simply a
static equilibrium analysis. We measure the deflection of a torsion pendulum
with and without the test masses present. I'm not sure what you are referring
to with the "flipping" procedure, but I'd guess it's more about homogonizing
erros rather than generating "force pulses".

~~~
datenwolf
> First off, thanks for engaging in a bit of debate. I came off a bit needly
> when I was trying to allude to a technical point.

Totally got that, no worries. And yes, I do see where you're coming from. But
I base my argument not on the concept of the quasi-static potentials of a
field theory with infinite speed of potential propagation (i.e. Newton).

> Even in a classical case, an external observer witnesses a periodic
> gravitational potential

But this assumes instantaneous propagation of the potential.

In every field theory in which changes (i.e. disturbances) of the field
propagate with limited speed any accelerating movement of the generating
sources of the field will create waves in that field.

Wiggle around some electric charge and you get EM waves carrying away energy.
Einstein's first (and failed) attempt toward a relativistic theory of gravity
was to apply the concept of retarded potentials. Didn't work out, something
was missing. But even in such a retarted gravitational potentials theory,
gravitational waves do show up.

> and cause Mercury to precess.

Isn't the precession of Mercury an effect of contraction of space by mass and
that at the radii of perihel and apehel the metric of space is different?

Even the tiniest spec of dust moving at Mercury's orbit should experience the
same precession, yet will radiate much less energy away through gravitational
waves, as far as I understand it.

> but that's not what we typically mean by "gravitational waves" which are,
> formally, metrics admitting a covariantly null vector field.

Yes I know, GR permits for additional wave modes, that you don't have in e.g.
electrodynamics in the vacuum. But I think it's dishonest to dismis the more
"mundane" modes to be not gravitational waves.

As far as I see it, in any field with limited propagation delay, any
disturbation propagating through the field is a true wave in a its right in
that field. If you want to reach a fundamental theory which can be applied
universally without the requirement of a-priori choices being made on the
system modelled, all aspects of the theory must be "enabled" all the time.

> As such, we can safely analyze it within the realm of Newtonian mechanics
> which only admits DC offset "gravitational waves"

… which is what I was saying by having long integration times. And as far as
nature goes, in any real system there is no true DC offset, because that would
require integration from -inf to +inf. Yes, I did mention "DC", but in a
practical sense DC just means "frequency which interval is an order of
mangitude longer than the integration time of the observation".

Here's a little food for thought: Say you have an mechanical shutter and shine
some long coherene (= narrow bandwidth) laser through it. Then you quickly
close and open the shutter. How does the spectrum of the light look like after
the shutter? Integrating over the spectrum before and after the shutter does
the power change? If so where did the delta in energy go / come from?

This is some practical wave dynamics engineering we laser guys do on a regular
base and solely rests on the fact that in a universe of finite age there is no
such thing as a true DC component; you can get infinitesimally close to DC,
but never reach true DC in the first place. So for example we use (fast)
modulators to create spectral sidebands and even do things like carrier and
single sideband suppression to shape the light to our bidding; becomes really
interesting if you throw nonlinear effects into the mix that allow to all
sorts of up-/downconversion.

> I'm not sure what you are referring to with the "flipping" procedure, but
> I'd guess it's more about homogonizing erros rather than generating "force
> pulses".

You're remembering right. What you do in the Cavendish experiment is to rotate
the big masses by 90° so that the torsion pendulum is twised in the opposite
direction, so that offsets in the pendulum cancel out. However consider this:
Instead of moving the big masses at descrete times, let them (slowly)
oscillate, maybe at the resonance frequency of the pendulum. If the pendulum
has a high Q factor it will eventually reach quite the significant oscillation
amplitude.

So what is this? I'd say this is energy transfer through gravitational waves
in the near field.

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Falkvinge
Hurra: yet another way for the NSA to exfiltrate data from my keyboard.

~~~
electrograv
Do you have fingers forged from the core of a neutron star? :D

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fsiefken
So what in what scenario would it be more practical to send a letter through
gravitational waves rather then light?

~~~
jobigoud
Maybe if there is a medium between the emitter and receiver that scatters
light, like an atmosphere.

Or if you don't have line of sight because there is an occluding object like a
planet or star in the way.

Or you have line of sight but it's really close to a super bright object so
you can't see anything.

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babuloseo
would be great for a doctor who episode, I dunno

