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How would a passing gravitational wave look or feel? (2017)

physics.stackexchange.com

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Re: How would a passing gravitational wave look or feel? (2017)

#21

Post by CGMthrowaway »

spauldo wrote: post #14
maaaaattttt wrote: post #3

On a somewhat related note I'm wondering what the expansion of the universe means for our bodies and matter in general? I think, like the accepted answer suggests, the forces on the atomic level make it so that larger structures get back to a certain equilibrium even if constantly streched equaly in all directions. But I have a hard time imagining what the universe expanding really means on a human/solar system scale…

Matter isn't pinned to the space it's in (source: try walking around). As space expands, the other forces which are orders of magnitude stronger than the expansion of space slide matter along so that distances don't change. You can only detect the expansion of space by measuring the distance between things that are so spread apart that the other forces between them are essentially zero.

That's an interesting point. The expansion of space still impacts matter on an atomic level though. The space between atom core and electrons influences its bonding abilities and other properties

Analogy, take two attracted magnets, or two opposing electrodes, and expand the space between them. Things change

Re: How would a passing gravitational wave look or feel? (2017)

#23

Post by maaaaattttt »

spauldo wrote: post #14
maaaaattttt wrote: post #3

On a somewhat related note I'm wondering what the expansion of the universe means for our bodies and matter in general? I think, like the accepted answer suggests, the forces on the atomic level make it so that larger structures get back to a certain equilibrium even if constantly streched equaly in all directions. But I have a hard time imagining what the universe expanding really means on a human/solar system scale…

Matter isn't pinned to the space it's in (source: try walking around). As space expands, the other forces which are orders of magnitude stronger than the expansion of space slide matter along so that distances don't change. You can only detect the expansion of space by measuring the distance between things that are so spread apart that the other forces between them are essentially zero.

That's what I understood from the explanation on stackexchange. But given what you said, if we take the plank length as the shortest length unit, and we consider two theoretical "objects" placed at one plank length away from each other. Does the universe expanding for these two objects mean: 1. the plank length is becomming bigger, 2. more plank lengths are added in between the two objects, 3. Something else and I'm completely off

Re: How would a passing gravitational wave look or feel? (2017)

#27

Post by NitpickLawyer »

3cats-in-a-coat wrote: post #5

Gravitational waves move at the speed of light, doubtful you can "look" at it. If it's that strong it'll just seem like a shake. Like an earthquake. Except it's the universe that's quaking.

> Gravitational waves move at the speed of light

Do we know if there are mediums (sp? media?) where gravitational waves move slower than the speed of light? Like light does in glass?

Re: How would a passing gravitational wave look or feel? (2017)

#28

Post by eggn00dles »

spauldo wrote: post #14
maaaaattttt wrote: post #3

On a somewhat related note I'm wondering what the expansion of the universe means for our bodies and matter in general? I think, like the accepted answer suggests, the forces on the atomic level make it so that larger structures get back to a certain equilibrium even if constantly streched equaly in all directions. But I have a hard time imagining what the universe expanding really means on a human/solar system scale…

Matter isn't pinned to the space it's in (source: try walking around). As space expands, the other forces which are orders of magnitude stronger than the expansion of space slide matter along so that distances don't change. You can only detect the expansion of space by measuring the distance between things that are so spread apart that the other forces between them are essentially zero.

Matter is very much pinned to the space its in. If the space between two galaxies expands, the distance between the two galaxies grows. If matter wasnt pinned the distance between the two galaxies would remain the same despite the expansion.

Things dont fall to the ground because the earth pulls on them. Earth is pulling in the space around it, and those things come with it. See the river model of general relativity for a more thorough explanation.

Re: How would a passing gravitational wave look or feel? (2017)

#29

Post by kmm »

maaaaattttt wrote: post #3

On a somewhat related note I'm wondering what the expansion of the universe means for our bodies and matter in general? I think, like the accepted answer suggests, the forces on the atomic level make it so that larger structures get back to a certain equilibrium even if constantly streched equaly in all directions. But I have a hard time imagining what the universe expanding really means on a human/solar system scale…

Without taking into account dark energy or a cosmological constant (so on scales smaller than a few hundreds of millions of lightyears), in the usual cosmological model you can see the expansion of the universe simply as a remnant of the initial kick all matter got from the Big Bang. There is no active pushing anymore, it's just matter moving apart, constantly slowing down due to the mutual gravitational attraction.

So for our bodies, planets, solar systems, even galaxies and clusters, because these are bound (either electromagnetically or gravitationally), the influence of the expansion of the universe on them is not just negligible, it's non-existent.

It's a little different when wo do include dark energy and other mechanisms more complicated than a simple matter or light content. For your intuition, you can think of this as a constant omnipresent negative pressure. We have no idea how it works on scales smaller than those of the observable universe, but if we imagine it works the same on every scale, then it's an extremely tiny force constantly pulling your body apart.

Re: How would a passing gravitational wave look or feel? (2017)

#30

Post by spwa4 »

eggn00dles wrote: post #28
spauldo wrote: post #14

Earlier quoted context omitted.

Matter isn't pinned to the space it's in (source: try walking around). As space expands, the other forces which are orders of magnitude stronger than the expansion of space slide matter along so that distances don't change. You can only detect the expansion of space by measuring the distance between things that are so spread apart that the other forces between them are essentially zero.

Matter is very much pinned to the space its in. If the space between two galaxies expands, the distance between the two galaxies grows. If matter wasnt pinned the distance between the two galaxies would remain the same despite the expansion. Things dont fall to the ground because the earth pulls on them. Earth is pulling in the space around it, and those things come with it. See the river model of general relativity…

I think the point is that the force of gravity is so much stronger than the expansion that the (equivalent) force a normal-sized star exerts on your body from the other side of our galaxy is greater than the force expanding space between you and that star. One of them, not all of them together.

All of them together are so much stronger it's not even funny. And that's for the "underdense" region that we are in. Not a void, but about half of our galaxy's environment does count as a void.

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