Is our observable universe "shrinking"? Because the universe's expansion is exponential...

Well according to special relativity, the speed of light is absolute - something about the faster something travels, the more massive it gets and the more time slows, until you reach the speed of light - and time stops altogether.

I didn't say, "faster than the speed of light."

If that's the case shouldn't objects move closer towards our field of vision?

it's "shrinking" because everything is accelerating away from everything else; which means at a certain point light won't be able to reach us as things appear to be moving away from each other 'faster than the speed of light'

this acceleration is caused by spacetime expanding, which is what has always been happening since the big bang; a rapid expansion

>I didn't say, "faster than the speed of light."
>at the speed of light
it doesn't make a difference which you said

What about in the meaintime?

What? The universe IS expanding 'at the speed of light... Look it up

imif it's like that then yes, observable universe would be shrinking
i see. is dark matter stuff (sorry for crude terms) possibly making any changes in those theories? since it's still to be studied and stuff
gayest question now: light has mass? it's a wave? if so, a wave of what?

also if universe is expanding at speed of light, and nothing can go faster than speed of light, how can it be accelerating?

what do you mean?

Photons (quanta [particles] of light) have no mass. It's actually called a 'wavicle', because it exhibits properties of both a particle and a wave.

Yeah. How?

My real questions is: if the universe has been expanding at the speed of light since the beginning, how is it we have been able to see galaxies almost as old as the universe itself (roughly 13.7 billion years).

Then how can anything travel?

idk im the brainlet
intriguing. i guess there's still lot do discover about light?

I think when they say the universe is expanding 'exponentially', it means things are getting further and further away because it happens all over the universe, i.e. 1-2-3, 1--2--3, 1---2---3?

As I said, everything is flying away from everything else at an increasing rate as spacetime expands; this means that relative to other places on the other side of the observable universe, they will appear to be moving away from us at faster than the speed of light. "At the speed of light" is a bizarrely specific and arbitrary speed.

I can't really say much about dark matter

In terms of light though, en.wikipedia.org/wiki/Wave–particle_duality
is what you're referring to
gl understanding it

Nothing with matter can reach the speed of light per special relativity, which is kind of a local ordeal

but when we talk about things accelerating away from eachother faster than light, it's referring to general relativity and spacetime expansion -- which is kind of a cheat way, and not really any sort of violation of the universal speed limit

Yeah. Although, most mysterious is gravity. We still don't know exactly what it is, there is no 'quantum theory of gravity' - it doesn't fit the standard model.

What do you mean? If you're confused about how everything can be appearing to move away from each other, it's simply because everything is accelerating "outward"; which gives the effect of everything moving away from everything else. The key word is accelerate, which is an increasing rate of velocity aka not constant

I don't know. But I read just now that the 'hubble horizon' is travelling away from us at the speed of light.

Yeah, apparently the website was inaccurate anyway. The approximate rate of expansion is 68km/s per megaparsec.

Meaning, if you look at a galaxy 1 megaparsec away, it will appear to be receding away from us at 68 km/s. If you look at a galaxy 2 megaparsec away, it recedes at 136 km/s. Three megaparsec away? You got it! 204 km/s. Et cetera

it hasn't been expanding "at the speed of light" since the beginning, it's not like that at all

places that are close to us aren't moving anywhere near the speed of light away from us; things much much farther away are, because things farther away have a larger acceleration "outward"

im not sure if i understand the second part, but if that makes sense then you should be able to piece it together

Refer to

ahh you triggered an old question of mine
does gravity has "effect" faster than light? i mean, if some object where to change mass or direction or whatever that can change his effect toward the rest, would this act immediatly or be like dead stars still lighting since it takes time to light to travel?
sorry for poor exposition

ahh the hubble horizon is the theoretical sphere (i assume it's a sphere-ish) around us in which the light stops being able to reach us -- i worded that weirdly, but it's the point where something starts accelerating from slower to faster than the speed of light

but that doesn't mean everywhere is, of course places closer to us are slower, and places much farther from us will be appearing to go faster than the speed of light

The speed of light is a constant right?
For light it takes a given amount of time to travel between two points on a light beam. Even when the length of the beam is expanding along with the universe... even when the two points are moving further away from each other... it takes the same time for the light to travel.
In case these assertion are accepted...

how can anything travel when the universe is expanding at the speed of light? The two points would stretch appart at the speed of light, how could a beam pass them?

general relativity calls for gravitational waves to travel the speed of light

en.wikipedia.org/wiki/Speed_of_gravity

>how can anything travel when the universe is expanding at the speed of light
see:

also you should look up the universe expansion rate

Physics 202, electricity and magnetism student here. I answer every question the teacher asks and pose questions that I know the answer to because the brainlets behind me will glean some use out of the answer. On tests I go beyond answering trivial questions and give detailed explanations and proofs for my work. Haven't lost a point yet. Face it: those "annoying kids" in class are more intelligent than you.

So my understand is that the universe is expanding at a constant rate of about 68 km/s per megaparsec, so it only appears as though it is travelling at the speed of light at the edges of the observable universe - but it is in fact, at an exponential rate, relative to the observer.

> the brainlets behind me will glean some use out of the answer
if that's how you want to rationalize it

Are you planning on going to grad school?

It's usually pretty obvious where their confusion is. I ask the questions they don't know they should ask.

I am a CS student. This is the last class I am taking before transferring. I enjoy physics though, so I might double major in it and see where I go from there.

close enough, im sure there's an actual astrophysicist here that can explain the expansion of the universe more clearly

i mean, the expansion isn't actually constant; it's expanding at an increasing rate -- which is why i say everything is accelerating away from everything else -- which is why things closer to us appear to be going slower than things farther from us

also, it only appears to be "traveling at the speed of light" at the hubble horizon .. which is the very specific "horizon" around us. you need to drop the whole " at the speed of light " thing because it's just confusing you

yes there is a place in every direction where this happens, but it's a specific place and has nothing to do with the overall expansion of the universe

I know that. But since the rate of expansion is essentially infinite, it appears to be travelling at the speed of light near the horizon, relative to the observer (i.e. wherever they are in the universe.

brainlet here
keep doing it, we need your help

So, how "fast" are things moving away from us, at the extreme range our our vision?

No.

The amount of matter in the observable universe increases because the speed of light is faster than the expansion. Over time we will get to see more and more of the universe and light from further away reaches us.

>edge of the universe

No such thing, kid.

how about edgelord of the universe

i think that question is a bit more complicated than it seems, since at the extreme range of our vision things are obviously appearing to be far into "the past" so to speak

also, someone can correct me if im wrong, but i imagine that data from that far away is pretty unreliable

i haven't read this all the way through since i have major add right now but this seems to be relevant to what you're looking for perhaps: blogs.discovermagazine.com/badastronomy/2009/05/07/the-universe-is-expanding-at-742-kmsecmpc/#.WKruPm8rKJA

True but not entirely true
>galaxies at a distance of 4,740 megaparsecs and redshift of 1.69 that are just now reaching the critical point, while galaxies at a redshift of 1.4 are still emitting light that will eventually reach us.

...

>But since the rate of expansion is essentially infinite, it appears to be travelling at the speed of light near the horizon
No. The rate of expansion depends on the distance from the observer. At the hubble horizon, the rate of expansion is equal to the speed of light. Past the hubble horizon, the expansion rate is faster than the speed of light. We can actually see objects that are past the hubble horizon, because they released their light before they passed the hubble horizon and so their light still has time to reach us. So even though we can't technically observe anything moving faster than the speed of light, we can infer that they are moving faster than the speed of light because of the redshift in the light.

Emitted light will eventually reach us regardless of the status of the origin of that light and whether or not it even exists by that time.

this

thank you i couldn't articulate or imagine that as well as you could which is why i never responded to him

This video might help explain why the hubble sphere is not the same as the edge of the observable universe.
youtube.com/watch?v=XBr4GkRnY04

No because the space between us and the approaching light particle is expanding faster then the speed of light.

That's exactly what I said. I don't know why people keep deliberately misunderstanding me. I said the 'rate of expansion is essentially infinite' because it appears to be getting faster and faster the further you look, because it has a compound effect (68 km/s per megaparsec - so 10 megaparsecs away it will 'appear' to being expanding at 680 km/s) towards the hubble horizon.

quora.com/Is-the-observable-universe-shrinking

I watched a video the other day, a famous physicist (can't remember who - think it was Brian Cox) said we will not be able to see anything past the current 'edge' of the universe, because the expansion is too quick and the light from stars outside the observable universe will never reach us.

I'd like to see that drawing done more accurately. It's essentially just a radial, logarithmic plot but with too many inaccuracies.

We have decent logarithmic maps of the whole universe, pic related.

Someone just take this map, convert to polar coordinates, add accurate color. Do it for the good of Veeky Forums, anons.

I only used it because it showed clear boundaries for the observed universe (making my point clearer).