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What Is Space?

nautil.us

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Re: What Is Space?

#21

Post by plaguuuuuu »

ingenuous2 wrote: post #20
obastani wrote: post #19

Earlier quoted context omitted.

A sibling post talked about special relativity, but you don't need special relativity to answer this question, just Galilean relativity. The answer is that you can measure velocity in any inertial reference frame you want. If you are in an inertial reference frame, you can say your own speed is 0 km/hr, or you can consider an inertial reference frame of the galaxy, which is some ungodly number, or you can measure you…

That is to say, everything is in an inertial reference frame, so there is no absolute center. Just like we can only mark a distance traveled as from a starting point.

Easiest way to think about it: Picture two satellites crashing into each other. It looks exactly the same if both satellites are doing 100 m/s, or one satellite is stationary and the other is doing 200 m/s.

>1. When does this stop? What is the most supreme center in the universe?

Is one of the above satellites the centre? The other? It doesn't change anything about the impact force. There's no physical difference. So we can choose either satellite to be the centre (0 km/h) or neither (100 + 100, 50 + 150, whatever)

>2. Just as the child could roll down his window, and have instant access to the outside, is there a way we can do the same?

The problem with the earth is that it's really big/heavy and gravity prevents stuff just sort of "hanging in the air" at human-height, relative to the rotation of the earth... speaking in practical terms, I mean.. so it's harder to visualise. But at the same time, sure. If you're on the earth, sitting in your chair, doing 0 m/s relative to the ground, and a satellite hanging around at head height that ISN'T rotating along with the earth hits you in the face, you just successfully accessed an intertial reference frame that's outside the earth :D

Re: What Is Space?

#22

Post by graycat »

Do we know enough yet to have some good guesses about

(1) the purpose of the universe,

https://news.ycombinator.com/item?id=14570170

(2) the end of the universe, (A) big expansion and cool down to nothing, (B) no more expansion and cool down to nothing, (C) contraction back to another big bang, (D) something else very different?

Re: What Is Space?

#23

Post by lgas »

worldsayshi wrote: post #18
gizmo686 wrote: post #5

Earlier quoted context omitted.

The biggest issue I see with the goo metaphor, is that it seems to suggest some sort of stationary ether that we move through as we move through space. That is to say, the mathaphor suggests that it makes sense to differentiate between stationary objects and moving objects in an objective sense. However, the core insight of relativity is that there is no such distinction.

This seems like a inevitable issue with any metaphor. It will always supply unwanted associations.

Yes, but its still worth being intentional about which ones you allow/support and which ones you don't.

Re: What Is Space?

#24

Post by lwansbrough »

Great read. What intrigues me - based on the description offered by the author - is that the leading theory seems to more or less try to side-step the existential problem of space. The author referred to this as "super space" -- but is it really? Or is it possible that in attempting to simplify the model - or worse - fit it to a prior assumption, we've actually taken a wrong turn in our understanding of the universe?

I'm not trying to say that the theories surrounding our current understanding of the universe are wrong. But they do seem to conveniently leave out one of the most vexing aspects of the entire problem. Where did it all come from? What's beyond "super-space"? Or, what's its container?

Re: What Is Space?

#25

Post by cyphar »

narrator wrote: post #14

One thing about space that I didn't see mentioned in the article is that even in a complete vacuum billions of miles away from anywhere there is still inertia. If something spins around it will still experience centrifugal force, so this is an absolute property of space and the universe that isn't caused by interaction with another body.

That's because rotation is a form of acceleration, and you can measure the acceleration (or if you prefer, the gravity) of a non-intertial (accelerating) reference frame. Galilean relativity only applies to inertial reference frames.

Re: What Is Space?

#26

Post by jacobolus »

Razengan wrote: post #16

Some related questions that I don't know where, or how, to ask: - Is there a “quantum” of space? Where/how is location stored? - If electromagnetic repulsion is what makes matter “take space”, and if virtually all macroscopic phenomena are governed by electromagnetism and gravity, then could this reality be said to be “gravelectromagnetic”, and might there be other “dimensions” governed by other forces, like “cones”…

From what I understand nobody knows the answer to your first question, but there’s been speculation both ways.

As for your second question, you might want to start with something like Feynman’s book QED.

Re: What Is Space?

#29

Post by ChuckMcM »

This continues to be one of my favorite questions.

In high school we were creating a vacuum in a bell jar to do the 'drop a feather and drop a weight' experiment and my physics teacher asked it. "So if we didn't have our apparatus in there, and we sucked it dry, what would be in there?"

It makes a great interview question because it helps identify people who have a hard time holding an unknown concept in their head and working with it.

I asked that of one of the folks I interviewed for Google when I was there and we spiraled off into a discussion of branes and multi-dimensional manifolds and quantum wave equations[1].

[1] Fun interview and they got the job :-)

Re: What Is Space?

#30

Post by cyphar »

graycat wrote: post #22

Do we know enough yet to have some good guesses about (1) the purpose of the universe, https://news.ycombinator.com/item?id=14570170 (2) the end of the universe, (A) big expansion and cool down to nothing, (B) no more expansion and cool down to nothing, (C) contraction back to another big bang, (D) something else very different?

> (1) the purpose of the universe,

This question is far more philisophical than anything. Personally I subscribe to Camus' Absurdism[1] -- that our yearning for meaning and purpose is ironic given how uncaring and lacking in meaning our universe is.

> (2) the end of the universe

There are several theories[2], but from my understanding we need to better understand "dark matter" and "dark energy" (scare quotes because those names are really silly, since we know effectively nothing about either).

In particular, it appears that we live in a flat universe but the evolution of the universe becomes more complicated with the cosmological constant terms in the evolution equations (believed to correspond to dark energy). Effectively, the cosmological constant can be seen as an energy density that remains constant throughout the universe which means that the amount of dark energy increases as the universe expands. I believe we discussed the current theories in my second-year cosmology course, but I can't recall the conclusion (it wasn't taught very well).

[1]: https://en.wikipedia.org/wiki/Absurdism [2]: https://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe

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