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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

#111

Post by urinotherapist »

AdamH12113 wrote: post #106
dangond wrote: post #86

Earlier quoted context omitted.

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…

I've found it's easier to think about this stuff in two dimensions. The surface of a sphere (or the Earth!) has non-Euclidean geometry. Imagine two people standing some distance apart from each other at the equator. They both begin walking in straight-line paths due south. At first, their paths are parallel. But as they move toward the south pole, they begin to drift closer to each other, as though their paths were c…

If two people are in parallel, they will make two parallel circles. If two people aimed at a singe point, they are not in parallel.

Space-time is 4d array: array of framebuffers. You can stretch your mathematical model all day long, but you knowledge must be mapped to reality somehow. In model we have space-time, while in real world we have "physical vaccum" ("something nothing" or "phaccuum", for short). I prefer to name that thing "ether", because I like that word.

Re: Monster gravitational waves spotted for first time

#112

Post by criddell »

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.

> the faster you go, the slower your proper time appears to an external observer

From my perspective, it takes about 8 minutes for a photon from the sun to hit my eye. From the perspective of the photon, a little time has passed, no? Doesn't the atmosphere and passing through my glasses slow it down a wee bit? Can the photon "know" that its position has changed between emission and absorption? From the photons point of view, I must be very, very close to the sun, right?

Re: Monster gravitational waves spotted for first time

#113

Post by ben_w »

criddell wrote: post #112
alfiopuglisi wrote: post #100

Earlier quoted context omitted.

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.

> the faster you go, the slower your proper time appears to an external observer From my perspective, it takes about 8 minutes for a photon from the sun to hit my eye. From the perspective of the photon, a little time has passed, no? Doesn't the atmosphere and passing through my glasses slow it down a wee bit? Can the photon "know" that its position has changed between emission and absorption? From the photons point…

Light does slow in a medium, the statement presumes the light is in a vacuum.

From the point of view of the photon, "forwards" is, like time, a null[0] dimension.

[0] I may be using that word imprecisely, but I can't think of a better one.

Re: Monster gravitational waves spotted for first time

#114

Post by derefr »

criddell wrote: post #112
alfiopuglisi wrote: post #100

Earlier quoted context omitted.

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.

> the faster you go, the slower your proper time appears to an external observer From my perspective, it takes about 8 minutes for a photon from the sun to hit my eye. From the perspective of the photon, a little time has passed, no? Doesn't the atmosphere and passing through my glasses slow it down a wee bit? Can the photon "know" that its position has changed between emission and absorption? From the photons point…

It takes time for a photon to move in your reference frame, but time within the photon's own reference frame is not advancing at all during that. Within the photon's reference frame, the photon exists instantaneously, simultaneously, at its emitter and absorber. Its whole existence "brings together" the spacetime it was emitted from and the spacetime it is absorbed into, at a single 4D pinch-point. It's like the whole universe is squished flat into two hyperplanes of "everything behind the photon at time of emission" and "everything ahead of the photon at time of absorption", and those two hyperplanes have no distance between them.

> Doesn't the atmosphere and passing through my glasses slow it down a wee bit?

When a photon is travelling through anything other than vacuum, it's not "slowed down." It's repeatedly being absorbed and re-emitted. (Or rather, it's being absorbed, and new photons that happen to be mostly equivalent are being emitted.) The refractive index of a material is effectively a measurement of the likelihood of absorption, times the average per-particle time-delay between absorption and re-emission.

Re: Monster gravitational waves spotted for first time

#115

Post by AdamH12113 »

urinotherapist wrote: post #111
AdamH12113 wrote: post #106

Earlier quoted context omitted.

I've found it's easier to think about this stuff in two dimensions. The surface of a sphere (or the Earth!) has non-Euclidean geometry. Imagine two people standing some distance apart from each other at the equator. They both begin walking in straight-line paths due south. At first, their paths are parallel. But as they move toward the south pole, they begin to drift closer to each other, as though their paths were c…

If two people are in parallel, they will make two parallel circles. If two people aimed at a singe point, they are not in parallel. Space-time is 4d array: array of framebuffers. You can stretch your mathematical model all day long, but you knowledge must be mapped to reality somehow. In model we have space-time, while in real world we have "physical vaccum" ("something nothing" or "phaccuum", for short). I prefer to…

> If two people are in parallel, they will make two parallel circles. If two people aimed at a singe point, they are not in parallel.

In spherical geometry, the equivalent of a straight line is a great circle. There are no parallel great circles. That's why I used the phrase "initially parallel" -- at the starting point, both people's paths are at a 90-degree angle to the great circle connecting their locations.

I didn't want to get into "locally flat" vs. "globally curved" in something that started as an ELI5 thread.

Re: Monster gravitational waves spotted for first time

#116

Post by zzzeek »

automatic6131 wrote: post #7
sidcool wrote: post #4

Earlier quoted context omitted.

Theoretically it's impossible to travel through space at or more than speed of light. But space itself can move faster than light speed, and a warp drive would help something similar that you mentioned. That is possible theoretically. But the amount of energy or mass it needs is very high and no current technology (or in foreseeable future) can achieve it. So FTL remains a dream. My hunch based on nothing is that we…

It's fun to imagine the species in x-hundred years. My college physics professor once told us that in 500 years, physics professors will still teach Maxwell's equations in the format he was showing us. And honestly, I think he's right. Somethings we will do the same way for hundreds of years, like the wheelbarrow will still exist in 500 years as it has for likely the previous 5,000. Otoh, I doubt we will be going fas…

there will be "physics professors" in 500 years, I see we are being optimistic about humanity

Re: Monster gravitational waves spotted for first time

#117

Post by nyrikki »

criddell wrote: post #112
alfiopuglisi wrote: post #100

Earlier quoted context omitted.

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.

> the faster you go, the slower your proper time appears to an external observer From my perspective, it takes about 8 minutes for a photon from the sun to hit my eye. From the perspective of the photon, a little time has passed, no? Doesn't the atmosphere and passing through my glasses slow it down a wee bit? Can the photon "know" that its position has changed between emission and absorption? From the photons point…

No. From the photons perspective, there is no concept of time. Phase speed, group speed, shadows going faster than the speed of light, etc.. will all complicate using the concepts used to teach diffraction

Massless particles being required to travel at the speed of light is perhaps a lens to think about it.

Re: Monster gravitational waves spotted for first time

#118

Post by amelius »

DexesTTP wrote: post #19
amelius wrote: post #11

Earlier quoted context omitted.

How would someone _inside_ space make use of FTL movement of space itself?

To simplify, the same way that a surfer on the sea can use the movement of the sea itself (waves) to surf! An Alcubierre drive (they're theoretical) would basically constantly compress the time curve of spacetime in front of the craft, allowing the craft to "ride" this compression as it moves forward, which means that the local speed of light of the craft is faster than the speed of light of an external observer. Not…

Sorry, I don't get it.

Imagine you are on a rubber ruler. You can move at most 1 mark per second on the ruler. This is true regardless of how much the ruler is stretched or compressed.

So to move from mark 1 to mark 100 will always take the same time at top speed, regardless of any stretching/compression.

Re: Monster gravitational waves spotted for first time

#119

Post by photochemsyn »

Astronomy Picture of the Day has a nice graphic of this:

https://apod.nasa.gov/apod/ap230629.html

Spacetime is incredibly resistant to deformation, hence the tiny displacements and the need for long-baseline laser interferometry to detect these waves.

https://blogs.scientificamerican.com/life-unbounded/just-how...

Re: Monster gravitational waves spotted for first time

#120

Post by abecedarius »

AdamH12113 wrote: post #106
dangond wrote: post #86

Earlier quoted context omitted.

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…

I've found it's easier to think about this stuff in two dimensions. The surface of a sphere (or the Earth!) has non-Euclidean geometry. Imagine two people standing some distance apart from each other at the equator. They both begin walking in straight-line paths due south. At first, their paths are parallel. But as they move toward the south pole, they begin to drift closer to each other, as though their paths were c…

Maybe it's worth adding that in this way of thinking (intrinsic geometry of the surface), great-circle paths have exactly the property the GP brought up about straight lines: neighboring paths aren't shorter on one side and longer on the other. (If you think of them as 3-d paths then there's a shorter path below vs. longer above, but that's not part of the intrinsic geometry.)
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