TheBleachDoctor
Secretly a Cat
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How close are we to gravity control now?
Gravity waves finally detected, Einstein proven right
- Thread starter TURBODERP
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- astronomy physics relativity
FaeGlade Plural
Semper Legens
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- Land of Bureaucracy
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Define "control".
Is detecting something a measure of control? Producing it? Redirecting it? Only being able to redirect or produce it under certain circumstances?
Because hey, I am producing gravity right now. Of course, it's an utterly miniscule amount. I guess you didn't mean that.
So, pick a definition of "gravity control".
In all instances, the answer is most likely "still so far away that we can't tell how far away we are, or if it will ever be practically possible."
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- The Netherlands
Well, we know that gravitoelectromagnetism is a thing. Certain effects that work for electromagnetism have equivalents in gravity. For example, if you get a really heavy ring and spin it at relativistic speeds the frame dragging causes artificial gravity down the throat of the ring.
So all we really need for gravity control is a gravity equivalent of superconductivity (So we can move mass without pesky inertia). Once we figure that out we can start to build gravity controlling structures that don't require unobtanium to stay together.
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RRoan
Technogaianist
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- 'round a far, distant star
We modify gravity all the time. It's not hard, you just move heavy things around. Easy.
Vorpal
Neither a dandy nor a clown
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It's because of the principle of relativity. If the instantaneous signal is possible in one inertial frame, then instantaneous signaling must be possible in any other inertial frame. Thus (green signal is possible)⇒(yellow signals are possible). Of course, if you throw out the principle of relativity, you could keep causality by e.g. insisting that there is a global reference frame in which the signaling is instantaneous and no other FTL speeds are allowed.
In general, a Lorentz boost on a Minkowski plane acts like a rotation along hyperbolas with lightlike paths as their asymptotes, so you can boost any superluminal speed (including faster-than-infinite, i.e. directed below the spatial axis) into any other superluminal speed. So the principle of relativity would imply that any superluminal speed being possible implies that all of them are.
I think the biggest practical news here is that this measurement scheme even works. Before learning about LIGO, if someone told me that they're going to measure length changes to nearly one part in 1023 against the myriad sources of noise, I'd have thought them delusional. Just wow.
Thing is, in the GEM formalism, you don't even need the heavy ring. If you're just spinning around, then the gravitoelectric fields will be G = ω×(r×ω) and the gravitomagnetic field H = 2ω, thus essentially being centrifugal and Coriolis forces. You can always define the GEM fields given a congruence of observers just by taking the geodesic equation and grouping the connection coefficients in a certain way; you always get a gravitoelectric part, and gravitomagnetic part, and a some leftover tensor that depends on the time-derivatives of the spatial metric, which have no electromagnetic counterpart.
Morally speaking, there's a reason why Einstein insisted that the connection coefficients, rather than the Riemann curvature, be interpreted as the components of the gravitational field—because then the connection between gravitational field and inertia is conceptually direct: gravitational freefall is inertial motion. And since the centrifugal and Coriolis forces are just about the ur-examples inertial forces, there's it makes sense to consider them to be gravitational fields too. (That's not to say that the opposite view regarding curvature doesn't have its pros.)
The unobtanium is more realistic, tbh.
My only dissapointment is that this was so close to being a plausible scenario for a naked singularity to form but it whiffed. A naked singularity would have been SuperHappyFunTimes!tm for physics
edit: come to think of it "boom big enough to outshine the rest of the universe" sounds about right, so maybe it didn't whiff.
edit: come to think of it "boom big enough to outshine the rest of the universe" sounds about right, so maybe it didn't whiff.
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magic9mushroom
BEST END.
Gravitational waves. Not gravity waves.
Well, it would for some subsets of observers, as I understand it. Not for all of them - that's true time travel (going into your past instead of your elsewhere) and therefore must be slower than light in its (negative) speed. Although true time travel of information is demonstrably possible given the ability to utilise tachyonic signals.
Well, it would for some subsets of observers, as I understand it. Not for all of them - that's true time travel (going into your past instead of your elsewhere) and therefore must be slower than light in its (negative) speed. Although true time travel of information is demonstrably possible given the ability to utilise tachyonic signals.
NonSequtur
a body
This is the kind of thing I made this smiley for. Though strictly speaking, it's not much of a smiley...
magic9mushroom
BEST END.
This is the kind of thing I made this smiley for. Though strictly speaking, it's not much of a smiley...
Firefossil posted an image of it on the last page, and Vorpal explained it on this one. Relativity says that if you can go at any superluminal speed, you can theoretically go at any other superluminal speed (including negative ones) assuming that your tachyons hold for all subluminal reference frames (like how you personally can have any particular subluminal velocity by picking reference frames; it's just that your house will be moving at that same velocity). You can construct subluminal trips from summations of superluminal trips (e.g. go to Mars in one Earth-relative second and come back in another Earth-relative second), and those trips can, therefore, lead back into the past.
Or, looking at it another way, if you're travelling FTL between Earth and Mars, some observers will see you take off from Earth and go to Mars and some will see you take off from Mars and go to Earth (specifically, if from A's point of view you take off from Earth and travel FTL to Mars, there exists a B from whose point of view a superluminal you going FTL from Mars to Earth and a subluminal you spontaneously appear on Mars, and then the superluminal you annihilates with a subluminal you on Earth). Supposing you make the round trip, it is possible to arrange your velocities such that in all reference frames you "arrive" back on Earth before you "take off" (though either two or all four of your transition points through lightspeed will be of the "spontaneous generation/annihilation" sort, from any reference frame, hence the scare quotes).
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Richardson
CAN YOU HEAR THE PEOPLE SING?
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Once more, I still find this 'paradox' and/or time travel silliness to be constructed bullshit. If you can go superluminal, you've established a new maximum frame of reference point, and established a new speed limit. Going faster than C just means you've established that C is not the fastest frame of reference in the universe. It doesn't necessarily follow that you've invalidated causality, or that the constants that we can see are invalid. It just means that we can't see faster than C things because of our current frame of reference.
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This is why nobody should try to 'understand' relativity without actually comprehending the mathematics and theory behind it.
"Frame of reference" means a thing. It doesn't mean... whatever you're trying to stretch it to mean.
Also, the "constructed bullshit" is the idea of having causality in a world where faster-than-light travel is demonstrably possible. The universe is under absolutely zero obligation to be comprehensible to merely human minds.
Let me tell you why relativity is called relativity.
It is called relativity because Einstein's postulate was not that there is some sort of "frame of reference" involving C. It is called relativity because there is no single objective frame of reference. In fact, all frames of reference are correct.
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cB557
voOOP
No, these are made up words. I refuse to believe otherwise.
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Basically, magnets are fucking magical.
NonSequtur
a body
*blinks*
You... seem to be assuming that superluminal things are a possibility.
That's quite the assumption.
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Not unless we have some major breakthroughs in physics. Can't outshine the entire universe without breaking some solar masses worth of energy. We can make much weaker waves by swinging very heavy items around really quickly, but why would you bother?
Creating gravitational waves? Practically useless until we're a type 3 on the kardashev scale. At that point you could use them to superheat the core of a star, causing it to go nova much faster. Or other ridiculous tricks.
Detecting them is insanely useful because we can use it to figure out how physics works in extreme conditions. Maybe we'll finally figure out how to combine relativity with quantum mechanics.
Shimrod
.303 Bookworm
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- Fryslân
Well, you're correct. Those words are made up.
The concepts they describe on the other hand...
Vindictus
XENO
- Location
- Texas
They are made up!
By scientists.
Because they need new words to describe the fucking crazy shit they find.
EDIT- And, I mean, Superluminal for one is obviously the technical term for FTL
Here's the simple way of looking at it: the time distortion of travelling at c is such that from the perspective of light no time passes. In light's frame of reference it simply teleports from interaction point A to interaction point B
So in order to go faster than light you have to arrive before you leave. Because the speed of light is the speed of teleportation.
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Black Noise
Curious
- Location
- About 1AU from Sol
No. You need to understand that space is really really rigid, in the sense that it takes something as ridiculous as black holes or neutron stars orbiting each other or colliding to even get a noticeable signal. Even then, the noticing part requires absolutely ludicrous amounts of effort required to get sensitive enough instruments; the limiting factors are things like "shot noise" where the random nature of the laser photons hitting the detector adds a background signal level.
One reason gravity waves are so weak is because of conservation of linear momentum makes the dipole-moment vanish, so on top of an additional 1/c^2 factor and gravity being generally weaker,
Edit: corrected due to comment below, wave amplitude falls of with 1/r and energy with 1/r², as per conservation of energy for any waves carrying it from the origin system.
The really exciting thing about this result is that it validates the whole concept of gravitational observatories and marks an era of gravitational astronomy. This is important because for the first ~380,000 years things were everything was plasma nothing was transparent enough for light, but much like neutrinos, gravity doesn't care about things like "there's a galaxy in the way", and brings with itself information much closer to the beginning of things.
*incidentally, this is why you need GR for GPS to work, the effect turns out to be of a similar magnitude to the "different frames of references moving relative to each other" part with the satellites going a few km/sec.
Edit: There's a good reason why the effects are of similar magnitude; the whole 'thing' with GR is that acceleration and inertia is equivalent to gravity, so if the centrifugal acceleration balances out the gravitational potential, you would expect similar effects for other relativity-related things.
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I wonder (and will doubtlessly go on wondering for a very long time due to the quantum disconnect) how this functions on a micro-scale. If anything that moves generates (infinitesimal) gravity waves then anything that moves (very slowly) bleeds energy. For instance if the heat death of the universe is a misnomer because heat (being motion) will (very very) slowly degrade into gravity waves.
Vorpal
Neither a dandy nor a clown
- Location
- 76 Totter's Lane, Shoreditch, London, EC1 5EG
Regardless of whether you're kidding or not... it's actually a pretty simple thing if one remembers a bit of high-school coordinate geometry. In the Euclidean case, the curves of constant distance-squared from the origin are circles x²+y² = r². A rotation about the origin keeps this constant:
As a result, you can rotate any angle into any other angle—or another way to put it, any slope into any other slope. The latter is a more immediately useful because the usual slope m = Δx/Δy on an (x,y)-plane will turn into v = Δx/Δt on a (t,x)-plane: speed is a slope in spacetime.
In special relativity, the curves of constant interval-squared from the origin are hyperbolas -t²+y² = ±s². A rotation looks like this instead:
As a result, you can rotate any sublimunal speed into any other subluminal speed, and any superluminal speed into any other superluminal speed.
For people that remember how complex numbers work, a Euclidean rotation about the origin by an angle φ acts like (x',y') = eiφ(x+iy) with i² = -1, a Galilean transformation as (t',x') = eεφ(t+εx) with ε² = 0, and a Lorentzian transformation as (t',x') = ejφ(t+jx) with j² = +1. These correspond to complex numbers, dual numbers, and split-complex numbers, respectively, and though this connection isn't particularly useful in physics, it nicely illustrates that {Euclidean,Galilean,Lorentzian} cases form, in some sense, a trifecta of the simplest possible geometries. Given the empirical evidence of 'time is a thing', spacetime can't be Euclidean, so there's only two simple possibilities left.
A more physics-based approach can be found here, establishing that the Galilean and Lorentzian cases are the only possibilities consistent with the principle of relativity, under modest assumptions of isotropy of space and homogeneity of space and time.
A more physics-based approach can be found here, establishing that the Galilean and Lorentzian cases are the only possibilities consistent with the principle of relativity, under modest assumptions of isotropy of space and homogeneity of space and time.
Uh... c is a speed, not any kind of frame of reference. Anyway, if you have an inertial frame at some speed w, then speed w can't be invariant unless w = 0 (because the inertial frame trivially has zero speed relative to itself), and zero speed being invariant would mean that no pair of inertial frames can move relative to one another. But if speed w is not invariant, then it can't be the speed limit either.
Sorry, I don't understand what you're trying to say. But if it helps, nowhere in the FTL construction above is it assumed that the superluminal signals have an inertial frame. Obviously, we can communicate at the speed of light, and there is no inertial frame travelling at the speed of light either.
One thing you might be missing is that in relativity, c is not fundamentally the speed of light, but rather the invariant speed across inertial frames. It's only incidentally the speed of light because light happens to be massless, but it's completely consistent with relativity to have light be massive and travel slower than c. In that case, all it would mean is that the historical vocabulary to describe these things was really poorly chosen, but as as far as we can tell, light really is massless, so calling it such is harmless (or in any case photon mass is experimentally bounded by a ridiculuously tiny amount, no more than 10-24 of an electron mass or so).
To be fair, magic9mushroom explicitly said so: "given the ability to utilise tachyonic signals." It's a pretty hefty given, but it's a typical turn of phrase to introduce an assumption. Perhaps more common in mathematical contexts than others.
This has no connection to the latter problem, because the situation is overwhelmingly classical, and the news that general relativity is confirmed again changes absolutely nothing about the assumptions of competent people in quantum gravity. That GTR is correct is what they already knew anyway.
For black holes of this size, we can expect quantum corrections on the order of ℏc/(GM²) ~ 10-80. Abandon all hope, ye who enter here, because LIGO's already ludicriously high sensitivity would have to have been 80 orders of magnitude higher, to combine to about roughly one part in a googolplex.
Rather, what this does outside the immediate is provide good evidence that gravitational wave projects like eLISA would work. Because of terrestrial noise and comparatively short interferometer arms, LIGO can't detect gravitational waves at frequencies below about 10 Hz, but the space-based eLISA would have no such problems. As a result, it might even be possible to detect gravitational waves from the very early universe (that's part of what eLISA wants to do, anyway), but even if not, at least a much wider range of astronomical sources.
While it's true that gravitational radiation requires a changing quadrupole moment rather a dipole moment as electromagnetic radiation does, and this definitely affects how hard it is to produce strong waves, the gravitational wave energy is still ∝1/r² and amplitude ∝1/r as usual. The latter is what's important here, as it's directly related to the strain observed by LIGO.
Well said. This whole thing is an experimental triumph. I'm making a note here: huge success.