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Monster gravitational waves spotted for first time

nature.com

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Re: Monster gravitational waves spotted for first time

#201

Post by jessriedel »

Solvency wrote: post #197
jessriedel wrote: post #53

Earlier quoted context omitted.

Yes, that's basically right. The gravitational way has a direction (say, z) in which its propagating. Within the plane perpendicular to that direction (x-y), a circular ring of particles will at at one moment experience squeezing in one direction (x) and stretching the perpendicular direction (y). As the wave passes through and you move from the peak of the wave to the trough, the directions reverse, so the first dir…

"However, spacetime is incredibly stiff, and I think all the known real-world sources produce pretty smooth waves." In English, why does stiffness correlate to smooth waves? What does stiff spacetime mean? I'd have thought a square wave would be "stiff" as it's quite the opposite of smooth.

Imagine using a flick of your wrist to create a traveling transverse square wave in a string vs. in a long metal dowel. It's actually not so hard to create a smooth sinusoidal wave in a metal dowel. (It will be long wavelength, but it will be easily visible if you put your eye near one end and look down it.) But it would be impossible for you to make a square wave.

Re: Monster gravitational waves spotted for first time

#202

Post by derefr »

Solvency wrote: post #197
jessriedel wrote: post #53

Earlier quoted context omitted.

Yes, that's basically right. The gravitational way has a direction (say, z) in which its propagating. Within the plane perpendicular to that direction (x-y), a circular ring of particles will at at one moment experience squeezing in one direction (x) and stretching the perpendicular direction (y). As the wave passes through and you move from the peak of the wave to the trough, the directions reverse, so the first dir…

"However, spacetime is incredibly stiff, and I think all the known real-world sources produce pretty smooth waves." In English, why does stiffness correlate to smooth waves? What does stiff spacetime mean? I'd have thought a square wave would be "stiff" as it's quite the opposite of smooth.

I think what the GP was stating here were two independent reasons why we would find it hard to know what would happen if a gravitational square-ish wave interacted with spacetime: 1. spacetime is "stiff", and 2. there are no gravitational square-ish wave generators around to observe.

The two things are kind of related, though. One "natural" way to create a square wave in nature, is to "interrupt" a material transmitting a sinusoid wave, at the peak of its transmittance. And one way to do that, is to break through the modulus of elasticity of the material transmitting the wave, such that it switches from the elastic-deformation domain (transmitting the wave) to the plastic-deformation domain (ripping apart.)

Imagine a speaker cone tearing at the peak of a high-amplitude drum beat. The cone pushes "out" — and then doesn't push back "in", because instead the air behind it rips forward through it. The air created by the speaker cone wants to rush back "in", but now there's no longer a speaker cone acting as a waveguide for the inward flow, so the natural turbulence cancels out much of the "falling" energy of the wave, making it look much more like a square-wave drop.

I believe that the GP is saying that, because spacetime has such a high effective "modulus of elasticity", we haven't yet observed any practical way to perturb so as to create the conditions that would generate a gravitational square wave.

Re: Monster gravitational waves spotted for first time

#203

Post by sliken »

zeven7 wrote: post #136
xattt wrote: post #134

Earlier quoted context omitted.

I was thinking more along the lines of a chemical or nuclear reaction (or some yet-to-be-conceptualized space-time reaction) at near an initiation point, but not quite there. I assume the gravity wave could push the reaction to initiate by warping a subatomic element (like an electron orbital) into an otherwise impossible configuration on a scale of picometers for a split second.

These gravity waves aren't strong enough to pull us off Earth. Everything on Earth is already subjected to gravity, and it doesn't cause nuclear reactions. Gravity waves won't cause impossible configurations to become possible.

Well it depends. How big a wave are we talking about? The ones so far have been very distant. But when to 100 solar mass black holes merge and form a 90 solar mass black hole they release 10 solar mass of energy (E=mc^2 strikes again). Being close to such a merge would be lethal.

However there's nothing that we know of that could happen close by, so the risk is near zero. Apparently the black hole at the center of the milky way is going to merge with another super massive blackhole in Andromeda in 4.5 billion years or so.

Re: Monster gravitational waves spotted for first time

#204

Post by jayjader »

cyberax wrote: post #159
staunton wrote: post #124

Earlier quoted context omitted.

> If all of that energy could be harnessed; it would be sufficient to power a small toaster oven. Do you have a source? Sounds like an interesting calculation.

The formula for the power of gravitational radiation for two orbiting objects is: W = 32 * G^4 / (5*c^5*r^5) * (M1*M2)^2 * (M1 + M2). "r" is the orbital radius, "G" is the Newton's constant, "M1" and "M2" are the masses of the orbiting objects. It's actually kinda amazing that once you substitute in all the values and do the math, all the scary large powers just somehow cancel out to leave a small macroscopic number…

Agreed; it's very serendipitous that you can basically light up a room with the gravitational energy that the sun/earth pair radiate out into space.

Light up 1 room with an incandescent bulb, or your entire flat with LED bulbs nowadays. I would be very interested in seeing some napkin math, based on power efficiency progress and "rate of technological innovation", that attempted to project when we could feasibly run the equivalent of our present-day human civilization purely off of gravitational waves/radiation.

Re: Monster gravitational waves spotted for first time

#205

Post by tremon »

Solvency wrote: post #197
jessriedel wrote: post #53

Earlier quoted context omitted.

Yes, that's basically right. The gravitational way has a direction (say, z) in which its propagating. Within the plane perpendicular to that direction (x-y), a circular ring of particles will at at one moment experience squeezing in one direction (x) and stretching the perpendicular direction (y). As the wave passes through and you move from the peak of the wave to the trough, the directions reverse, so the first dir…

"However, spacetime is incredibly stiff, and I think all the known real-world sources produce pretty smooth waves." In English, why does stiffness correlate to smooth waves? What does stiff spacetime mean? I'd have thought a square wave would be "stiff" as it's quite the opposite of smooth.

In order for a square wave to travel through a material, it would need to allow for infinitely high frequencies (see the animation on wikipedia[0] for a visual demonstation). The lower the maximum frequency possible, the more every wave will resemble a sine wave because it's the most basic shape: any non-smooth wave has higher-frequency components to give it its shape. Filter out those higher frequencies, and you're left with the basic smooth sine wave again.

A stiff material tends to dampen high frequencies, simply because it cannot deform fast enough to follow the wave's shape. In a way, the medium acts as a low-pass filter; compare, fow example, how fast you can clap your hands in air vs in water: the stiffness of water slows down your movements so you cannot reach high clapping frequencies.

[0] https://en.wikipedia.org/wiki/Square_wave?useskin=timeless#C...

Re: Monster gravitational waves spotted for first time

#206

Post by raattgift »

cyberax wrote: post #159
staunton wrote: post #124

Earlier quoted context omitted.

> If all of that energy could be harnessed; it would be sufficient to power a small toaster oven. Do you have a source? Sounds like an interesting calculation.

The formula for the power of gravitational radiation for two orbiting objects is: W = 32 * G^4 / (5*c^5*r^5) * (M1*M2)^2 * (M1 + M2). "r" is the orbital radius, "G" is the Newton's constant, "M1" and "M2" are the masses of the orbiting objects. It's actually kinda amazing that once you substitute in all the values and do the math, all the scary large powers just somehow cancel out to leave a small macroscopic number…

Can I ask how you got there? G^4/c^5 makes sense, but the rest loses me.

(Eventually after all the typing below I think that I traced the 32/5 and (M1*M2)^2 * (M1 + M2) to (eqn 16) in Peters & Matthews 1963 maybe? (e=0, a->r) https://doi.org/10.1103/PhysRev.131.435 (stick sci-hub.se in front of that if you need to). The authors take an approach comparable to the textbooks below.)

Super-quick textbook review. Practically all of them start with the quadrupole moment and try to justify an energy which is quadratic in derivatives of that while still within a linear theory. Carroll and Mathtias Blau take slightly different-from-each-other paths through the transverse-traceless TT-gauge to P = dE/dt = -2/5 \frac{G^4 M^5}{r^5} (c=1) for a circular equal-mass soft binary. Wald uses the radiation gauge and so eqn 4.4.58 looks fairly different, and comes with the amusing Waldian line "A lengthy calculation (where many terms which integrate to zero are dropped) yields the final result,". Sigh. Blau's development looks a lot like MTW, but the latter gives us .... Exercise 36.6 ("Apply the full formalism ... to a binary star system with circular orbits. Calculate ... the total power radiated; the total angular momentum radiated ..."). Gee, thanks thick textbook. FWIW, 90 seconds of that (mostly trying to make sure both sides have the same dimension rather than extracting a power in watts because bad/lazy reasons and anyway I always think you had about the right order of magnitude) doesn't take me to anything like the form of your calculation.

Rather than flip through other textbooks, let me rely on my maybe-shaky memory and say that most of them, at least the modern editions, follow the TT gauge approach and come up with an equation in a form similar to Carroll.

What stands out here is that Earth-sun has a large mass ratio and noncircular orbit, and it's not really a binary system anyway, and so will defy these textbook schemes. Secondly all of these take P in the far field, because linearization. (Compare that with your edit).

I also got way off into the weeds wanting to work with chirp mass (rather than q=m_1/m_2) which is what GW obs data analyses use because extracting the individual masses is hard. I also know a bit about EMRI BHBs (extreme mass-ratio inspiral) and in those dissipation is dealt with differently from textbooks even for soft binaries (e.g. soft->hard roughly PN & perturbative methods, EOB, GSF, numrel) absolutely none of which is of immediate practical use here.

So that's some of what motivates my question about the origin of your calculation.

ETA: I think most of what happened here is that my brain reads equations as words, and I simply forgot that I could actually rearrange teh ltteres! TGIF :-)

Re: Monster gravitational waves spotted for first time

#207

Post by zackmorris »

AprilArcus wrote: post #94
zackmorris wrote: post #80

Earlier quoted context omitted.

This video might help understand where mass comes from and how to potentially modulate it, because mass can be thought of as bound energy creating voids in the gluon field: https://m.youtube.com/watch?v=Ztc6QPNUqls The Higgs mechanism affects electrons, not quarks, and is only responsible for about 1% of matter's mass. Most mass comes from the binding energy between quarks, which creates flux tubes between quark-anti…

>The Higgs mechanism affects electrons, not quarks It effects both. The LHC produces Higgs particles through the annihilation of top-antitop pairs, which works because the top quark couples strongly to the Higgs field.

Thank you, that sent me down a Wikipedia crawl which connects the Higgs field to superconductivity:

https://en.wikipedia.org/wiki/Higgs_mechanism#Simple_explana...

This is a terrible analogy, I apologize in advance because I don't fully understand it yet, but:

We think of empty space as empty because its symmetry isn't broken, so it looks transparent to our matter as we move through it. Similarly to how electrons pair up to form cooper pairs, which act like bosons and pass through the atoms of a superconductor without interacting:

https://physics.stackexchange.com/questions/171132/what-is-t...

https://physics.stackexchange.com/a/273894

But the Higgs field permeates space, so if we could pick and choose where to interact with it, we could "grab" it and propel ourselves. This would be analogous to a magnet levitating on a superconducting ring, just like this video but imagine that the track is the superconductor and the puck is the magnet:

https://www.youtube.com/watch?v=AWojYBhvfjM

If we built a puck with two electromagnets, we could power up one of them above the critical field of the superconductor and form a resistive section which the other magnet would be drawn to or repulsed from:

https://en.wikipedia.org/wiki/Critical_field

By alternating the strength of the two magnets, the track would stop behaving as empty space, and the puck could accelerate along it like a maglev train. A similar technique should work with the Higgs field.

I don't know how much the Higgs field "weighs", so I don't know how much of a reactive force we would get for the force applied. My guess is that it either wouldn't be higher than light pressure, or that the probability of an interaction would stay beneath what's required to beat light pressure. As in, this may be tied to how often a photon splits into an electron-positron pair, with the remaining energy bleeding off as heat or entropy. But it would be a fun experiment to run.

I just want to add that physics terminology and notation is too big to fit in the human mind, like trying to memorize a 100 digit phone number. The same problem exists in functional programming, where stuff like monads and y combinators just won't stick in a mind trained on imperative programming. So there's a very real limit to what we can understand. No matter how long we study this stuff, we can never connect all of the dots, or see faint relationships between distant concepts. IMHO this problem is getting worse with time, despite the advances in stuff like the Standard Model.

But AI doesn't have that problem. Within 10-20 years, it will infer how to modulate stuff like the weak force and gravity with electromagnetism in a practical way. If the aliens can do it we can do it! Or we can at least build machines to tackle the problem faster than we ever could. And if that's true, then why bother keeping research secret? It's gonna all come out eventually.

Edit: added the Higgs mechanism derivation from superconductivity. Also wanted to add that axions (if they exist) only interact with gravity and electromagnetism, making them a potential bridge between the two:

https://en.wikipedia.org/wiki/Axion

Re: Monster gravitational waves spotted for first time

#208

Post by zackmorris »

UncleSlacky wrote: post #110
zackmorris wrote: post #80

Earlier quoted context omitted.

This video might help understand where mass comes from and how to potentially modulate it, because mass can be thought of as bound energy creating voids in the gluon field: https://m.youtube.com/watch?v=Ztc6QPNUqls The Higgs mechanism affects electrons, not quarks, and is only responsible for about 1% of matter's mass. Most mass comes from the binding energy between quarks, which creates flux tubes between quark-anti…

You should join us at APEC: https://www.altpropulsion.com/

Cool!

Re: Monster gravitational waves spotted for first time

#209

Post by euroderf »

alfiopuglisi wrote: post #100
sunshinerag wrote: post #97

Earlier quoted context omitted.

what does "photos don't experience time themselves.." mean? why not?

Photons travel at the speed of light, and at that speed, any "subjective" time is zero. In Einstein's theory of special relativity, the faster you go, the slower your proper time appears to an external observer. At the speed of light, this effect reaches infinity.

Okay, so what does a photon observe when it partakes of Cherenkov radiation ?

Re: Monster gravitational waves spotted for first time

#210

Post by euroderf »

ithkuil wrote: post #123
criddell wrote: post #121

Earlier quoted context omitted.

So from the photon's point of view, the entire universe is a single point?

No because a single photon doesn't *experience" the whole universe but only the points where it's emitted and absorbed and you could say all the points in between along the geodesic between the emission and absorption events

So if it is never absorbed, flying on thru the vast emptiness of space, does it experience the sum total of the existence of the universe ? (along that geodesic, of course)
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