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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

#151

Post by mtlmtlmtlmtl »

Modern physics(and engineering) is kind of absurd. And I mean that in a good way. LIGO? I didn't believe at all that it would ever work. Even when they got detections I kinda thought they were chasing their own tails. Now the evidence is pretty much rock solid that the data is real(multiple facilities, correlations with light observations for neutron star mergers, etc). Then I heard about LISA, which essentially is building this thing in fucking space(different geometry, but same basic concept), with probes somehow orbiting in unison and firing lasers at eachother over ridiculous distances(2.5 million kilometers!). I thought they were raving mad. But pathfinder, the POC, seemed to work, and now they're building the thing. Planned for 2037, but still.

When I heard about this project in a spacetime video a few years ago IIRC, again I thought okay, this is too far. It's never gonna work, there'll be too much noise yadda yadda. And it now it looks they might have done it.

At this point, if physicists say something is possible, I listen no matter how impossible it sounds.

Re: Monster gravitational waves spotted for first time

#152

Post by samstave »

dangond wrote: post #86
pantulis wrote: post #72

Earlier quoted context omitted.

Space itself means the metric of spacetime: how you measure distances. Locally, if there was no gravity, you could think of space as a plain reticule where distances would be calculated through eucledian geometry: that means cartesian distances, parallel lines would be parallel and the angles of a triangle would sum 180, and the shortest path between two points is the straight line. General Relativity successfully es…

Out of curiosity, from someone who has never worked with non-euclidean geometry, what does it mean for a path to be curved in non-Euclidean space? My outsider understanding of curvature is that the inside of a curve is shorter than the outside of the curve, whereas a line has the same length on either side (assuming we give these curves and lines some thickness). But, if the shortest path can be curved, what do we me…

Distance from center as described by the path - so if the distance to center is held, but the trajectory is changed, the line will be expressed as a curve around a tehtered point to the center.

If the 'tether' is a gravitational link (meaning that the teather, is a constant pull against the trajectory, regardless of the trajectory, the object will continue to curve around center.

Re: Monster gravitational waves spotted for first time

#154

Post by mcpackieh »

Probably a stupid question, but could you theoretically surf on gravitational waves? Obviously not on earth, but maybe near a binary black hole or something. If I imagine waves in a rubber-sheet mental model of gravity warping spacetime, it seems like surfing should be possible.

Re: Monster gravitational waves spotted for first time

#155

Post by jcarreiro »

mcpackieh wrote: post #154

Probably a stupid question, but could you theoretically surf on gravitational waves? Obviously not on earth, but maybe near a binary black hole or something. If I imagine waves in a rubber-sheet mental model of gravity warping spacetime, it seems like surfing should be possible.

Sadly, this is not possible, at least AFAIK. The basic problem is that a gravitational wave won't push against you, like a water wave would; the wave will pass through you.

See https://worldbuilding.stackexchange.com/questions/36113/woul... for a more detailed explanation.

Re: Monster gravitational waves spotted for first time

#156

Post by defrost »

mtlmtlmtlmtl wrote: post #151

Modern physics(and engineering) is kind of absurd. And I mean that in a good way. LIGO? I didn't believe at all that it would ever work. Even when they got detections I kinda thought they were chasing their own tails. Now the evidence is pretty much rock solid that the data is real(multiple facilities, correlations with light observations for neutron star mergers, etc). Then I heard about LISA, which essentially is b…

It takes a while to build these things.

My physics professor, David Blair, sketched out the design for LIGO and other detectors back ~1980 and the kinds of technology that would first need to be created in order to get there.

The big money and the big builds tend to be in the US (for now, at least, but empires always shift centres over the long time periods) but the ideas come from all over the world.

https://www.uwa.edu.au/Profile/David-Blair

Re: Monster gravitational waves spotted for first time

#157

Post by [deleted] »

Lichtso wrote: post #147
sam_goody wrote: post #139

Can someone please ELI5: I was taught that all items fall at the same speed, due to the gravitational constant. With these waves, does that mean that items will fall at ever so slightly differing speeds, as depending on the size of the wave there is a pull in the other direction, and the constant is slightly off? And OT, but related: Since every item has a gravitational pull related to its mass, would a bigger item f…

Well in both your questions it depends on how you define speed. It is commonly understood to be the first derivative of position, or the quotient of distance divided by a time-span. But how do you define and measure distance and time-spans? Which reference frame do you use? Also, the things falling in a vacuum at the same speed thing is a common misconception. The two arguments usually are that the mass of one body c…

[deleted]

Re: Monster gravitational waves spotted for first time

#158

Post by plewd »

Lichtso wrote: post #147
sam_goody wrote: post #139

Can someone please ELI5: I was taught that all items fall at the same speed, due to the gravitational constant. With these waves, does that mean that items will fall at ever so slightly differing speeds, as depending on the size of the wave there is a pull in the other direction, and the constant is slightly off? And OT, but related: Since every item has a gravitational pull related to its mass, would a bigger item f…

Well in both your questions it depends on how you define speed. It is commonly understood to be the first derivative of position, or the quotient of distance divided by a time-span. But how do you define and measure distance and time-spans? Which reference frame do you use? Also, the things falling in a vacuum at the same speed thing is a common misconception. The two arguments usually are that the mass of one body c…

> heavy and light bodies do experience the same acceleration, but a heavy body will collide sooner than a light body.

I still don't understand, why would the heavy body collide sooner if they have the same acceleration (and starting at rest)?

Re: Monster gravitational waves spotted for first time

#159

Post by cyberax »

staunton wrote: post #124
treeman79 wrote: post #89

Earlier quoted context omitted.

The earth going around the sun produces gravitational waves, and some of the energy is lost. If all of that energy could be harnessed; it would be sufficient to power a small toaster oven.

> 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 (I remember getting around 60 watts).

Edit: note, that both objects radiate. So it's 60 watts for both the Earth and the Sun, around 120W in total.

Re: Monster gravitational waves spotted for first time

#160

Post by roywiggins »

derefr wrote: post #61
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…

Acoustic waves propagate through what are essentially elastic deformations of the material they travel through. Can gravitational waves be thought of as propagating by elastically deforming spacetime? If this analogy holds, then can it be taken further? Acoustic waves dissipate their energy insofar as they trigger plastic deformation in a material. Could gravitational waves plastically deform... spacetime itself? Or…

They are predicted to leave permanent distortions in spacetime, though I think it's a more complicated mechanism.

https://www.quantamagazine.org/gravitational-waves-should-pe...

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