Comments
moonsoundsonsnow t1_ix70bsg wrote
but what is the reference point for which the velocity of the expansion of space is measured?
triffid_hunter t1_ix70n30 wrote
Doesn't matter.
Cosmic expansion behaves like new empty space is being injected everywhere all at once, not like some sort of border moving away from a specific point - ie more like bread rising in the oven than a spreading puddle.
Thus, the expansion of space looks pretty much the same from all locations.
This_Username_42 t1_ix74byy wrote
I went to undergrad for physics and took some (not many) Astronomy courses and I do not think I knew this. Thanks
IronSmithFE t1_ix7273z wrote
space is chaos, it doesn't move nor can it do anything else. it is the nothingness between matter.
Street-Badger t1_ix734ya wrote
Space itself is expanding everywhere we look, flinging distant objects away from us faster and faster. This is called the Hubble constant. Physicists have no idea why, so they call it ‘dark energy’.
Some of what you see in the night sky is already beyond our reach forever, even if we could travel towards it at 1.0c, because the objects have accelerated away from us in the interval since the light was emitted.
pineapplecooqie t1_ix73zsr wrote
space absolutely expands, and that expansion happens at a measurable rate. I've no idea what you think you're talking about.
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iwoodificood t1_ix6ze7u wrote
Upon boot-up the universe instantly poofed to an incredible size, after which the poofing slowed to a steady yet increasing pace.
This is pretty good explanation https://youtu.be/QhM5zAVvOI4
Loathsome_Dog t1_ix7jz2d wrote
Yes for evidence of this you only need to look at the cosmic background poofings
Elbynerual t1_ix6yec8 wrote
13 billion years of everything in the universe moving away in different directions
IronSmithFE t1_ix72xbi wrote
that would, at best, mean the universe is 26 billion lightyears in diameter. not 83.
magnamed t1_ix769qn wrote
How so. Nothing says that the space only doubled in that time.
Ooops2278 t1_ix7805x wrote
The original question is about a perceived contradiction. Or actually two...
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How can the universe have expanded faster than light? Then the answer that it expanded in different direction at the same time is not helpful as that indeed would limit it to 2 times lightspeed in opposing directions.
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How can we observe something 83 billion years away when the light did not have time to reach us in only 13 billion years? Which leads to the exact same problem when we assume light speed to be a cap. When we observe it now it must have been 13 billion light years away back then but moved (relative to our position) another 70 billion light years away since then.
So any answer about the expansion of the universe without addressing light speed is not helpful.
mrbrendanblack t1_ix714v0 wrote
It all started with a curry made with too much cabbage…
simcoder t1_ix6yhc3 wrote
There was a period of time where everything everywhere expanded in every direction. So there was some compounding going on.
See also: inflation
tmphaedrus13 t1_ix714y6 wrote
Inflation has even hit outer space?? Dammit, Biden! 😉
bkupron t1_ix6zh5s wrote
Inflation is still going on. It is just more noticeable when looking far away.
simcoder t1_ix70qid wrote
My theory is that mass holds space together on the local scale and it's mostly the space in between masses that's still expanding. Masses in this cases being galaxies and what not.
tigojones t1_ix6zqc9 wrote
The universe is expanding, and this expansion isn't bound by the "nothing can travel faster than light", because that only applies to things inside the universe, not the universe itself.
Ooops2278 t1_ix78h92 wrote
>and this expansion isn't bound by the "nothing can travel faster than light", because that only applies to things inside the universe
But what about the light inside the universe? How did it reach us from 83 billion light years away in under 13 billion years since the big bang?
IronSmithFE t1_ix72zt3 wrote
i don't understand this. the universe is defined by everything within it.
glieseg t1_ix75gzd wrote
Imagine you have a balloon. Paint some dots on it and blow some air in it. All the dots move away from each other because the balloon (the universe) is expanding, despite the dots not moving physically on the balloon.
The surface of the balloon itself is curved 2 dimensions, but the analogy works for the universe, too.
Kiezeus t1_ix7523g wrote
Long story short i) >>c expansion (hyperinflation) at the beginning of universe and ii) space between matter in the universe is expanding constantly that causes faster-than-light expansion (new-born empty space also expanses so the expansion is exponential and not limited by the speed of light). So again, new emerging space between the objects or the universe cause the universe to expand faster than light, although all objects in that space are not able to move faster than light in relation to each other.
IronSmithFE t1_ix9tv1v wrote
> space between matter in the universe is expanding constantly that causes faster-than-light expansion
at best you'd only get 2x the speed of light in expansion assuming objects were traveling in exactly opposite directions at the speed of light. since nothing but photons and gravity waves are traveling at the speed of light and neither are observable parts of the universe as they travel outwards the universe could not have expanded nearly 80 billion lightyears. at best it could have expanded to a diameter of 26 billion lighyears and that would not be nearly true because no matter what we can observe from our vantage point travels nearly the speed of light.
so, if the observable universe is indeed more than 80billion lightyears in diameter the initial hyperinflation would need have been the vast majority of the expansion of the universe and must continue to be the majority of the expansion for the next 27 billion years. now, because i have no idea how or why matter could have expanded faster than the speed of light your "short story" makes no sense to me.
perhaps you could tell me how matter or protomater could have expanded a great deal faster than the speed of light before you expect me to believe your short story.
Kiezeus t1_ixb96pw wrote
There is new empty space emerging from nothingness, and this is different thing that two objects travelling from each other. Think it like this: you and I are located still 1 lightyear from each other, and suddenly 10 light-years worth of new space emerges between us. It would endeed SEEM to us that we would have broken law of relativity, but actually we have not moved faster than light (or in this case, ww havent moved at all!) - there just have becomw more empty space between us. (Edit: accidentally posted too early)
IronSmithFE t1_ixbdi8t wrote
> There is new empty space
prove it.
the best you can say for sure is that distant massive bodies are accelerating away from each other. there are a few flimsy theories as to why it is happening, one of which is that there is some kind of dark matter between normal matter which is pushing normal matter around. even if that were the case, the motivation of normal matter would never exceed the speed of light.
Kiezeus t1_ixbit9y wrote
Hi, most accepted Dark Energy theory is not based on material/dark particles pushing objects away from each other, you may mix it with Dark Matter theory (explaining "missing" mass of galaxies etc). However, I see that this thread was to explain the issue that universe is larger than light speed would allow, and for this purpose explaining the topic on the currently accepted hypothesis/theories is logical to keep the answers simple. Discussing proving of the dark energy theory and especially doscussiong alternative theories for sure deserve their own thread.
ElliosRile t1_ix75hdg wrote
Imagine you have a balloon, and you have a bunch of dots on it. Things can travel along the surface of the balloon up to a certain speed in any direction. You can define the balloon based on where all the dots are and the surface in between them. However, if someone starts inflating the balloon, then everything is going to spread out and the surface is going to stretch. Since the expansion of the balloon isn’t travel along the surface of the balloon, it’s not subject to the same speed limit, so your dots can move away from each other faster then things can travel along the surface if the balloon.
IronSmithFE t1_ix9sa75 wrote
k, but the stars don't and can't move at near the speed of light and even if they did and two stars were traveling in opposite directions the furthest they could have expanded from each other in the fastest scenario assuming they did each move at the speed of light would still only be 26 billion lightyears. in your balloon scenario, they wouldn't move near the speed of light except in relation to each other and even then they would be unlikely to reach the speed of light in relation to each other.
ElliosRile t1_ixa069r wrote
I want to clarify, this isn’t “my scenario”, it’s a non-mathematical explanation of what we actually observe right now. When we measure the speed of galaxies far away from us, they’re receding at faster then the speed of light. You have to keep in mind that we are not talking about movement “within” the universe, where stars and matter don’t move anywhere near the speeds of light, we’re talking about reality itself expanding in all directions. We can actually observe the light emitted from those distant galaxies change its color, as the expansion of space causes the actually wavelength of light to expand.
glisteningdinkus t1_ix707hr wrote
The universe, meaning the particles and space and time were created in the Big Bang. The distances aren't just about the speed of galaxies and stars moving. It's about space itself expanding.
Ooops2278 t1_ix788pq wrote
That only answers one problem. Even if space itselfs expands much faster, how do we observe something 83 billion light years away if there are no 83 billion years for the light to travel?
glisteningdinkus t1_ix78j2r wrote
I just did a search and the farthest observed object is 13.3 billion light years away. Where did you get your number?
Ooops2278 t1_ix8ia58 wrote
From OPs question you answered?
His numbers and the premise of his question simply being wrong is indeed an answer.
triffid_hunter t1_ix70f1v wrote
hestalorian t1_ix79xn3 wrote
Here's Tom with the weather.
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Griasgott t1_ix76voj wrote
I am no physicist, so bear with ne here. It has to so with the expansion if space. One thing to note here is that space expands faster than light travels. How? Well, basically nothing IN the universe can move faster than light, but the universe itself can.
If space did not expand faster than light, then the size of the observable would indeed be equal to approx 27 billion ly end to end.
Imagine you are walking at a constant speed and whichever distance you cover is the observable universe. Now imagine that the ground you are walking on suddenly stretches forward several times faster than you are walking. You have covered the entire distance, but you have not moved any faster.
Or imagine a being in a jet. You yourself move at 0 km/h but your body covers the same distance as the jet.
Ape_Togetha_Strong t1_ix7cts0 wrote
The actual answer is that the starting distances are nonzero, and with nonzero starting distances, you can get any size with the right rate of expansion. The "initial singularity" with infinitely small size is a mathematical anomaly, a result of naively running things back in time further than we know how to.
No rate of expansion, when multiplied by 0, gives you a positive distance. Something with infinite density cannot expand to something with finite density. The initial state of the universe as far as we are able to talk about it is hot, dense, and low-entropy, but it is not infinitely small.
So, any answer that involves some rate of expansion as the reason is incomplete, because without nonzero initial distances, you just get zero expansion.
Now, with all that out of the way, the answer to "how can the universe be 93 billion lightyears across if light has only had 13.7 billion years to travel" is just that the way we talk about the size of the observable universe is about how far apart those things would be from us now, at this moment in cosmic time (their comoving/proper distance). The majority of the observable universe is already unobservable, if by "unobervable" you mean "light emitted from it right now will never reach us". But we can see their past, and thus they're part of the "observable universe".
8amflex t1_ix7i52m wrote
This article:
https://bigthink.com/starts-with-a-bang/see-back-space-time/
Does a really good job at explaining this phenomenon in layman's terms so even people like me can get a vague understanding of it.
space-ModTeam t1_ix7jibx wrote
Hello u/novacks0001, your submission "Someone tell me how the Big Bang began 13 billion years ago, yet the observable universe is 83 billion light years apart?" has been removed from r/space because:
- Such questions should be asked in the "All space questions" thread stickied at the top of the sub.
Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.
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CBeisbol t1_ix6zymh wrote
(60 * 2) + (60 * 2) = 240
So
13 + 13 = 83
Err...wait
Czl2 t1_ix71ioi wrote
> Someone tell me how my friend and I began driving in opposite directions at 60 miles per hour two hours ago, yet now we’re 240 miles apart?
You are driving away from each other on the surface of a rapidly inflating balloon. Your velocity from each other needs to be added how fast the balloon surface is stretching / growing. Even if you both stop your cars you will continue moving apart due to continuing inflation.
Ooops2278 t1_ix799i0 wrote
But if the universe's "surface" is expanding faster than light how do I observer something?
Czl2 t1_ix7f4y6 wrote
> But if the universe's "surface" is expanding faster than light how do I observer something?
Those parts of the universe are not visible as they are now. However light travels at a finite speed and what you're looking at today is what happened when the light you see today long ago started traveling towards you.
Ooops2278 t1_ix8hxgk wrote
Still doesn't work. If the observable parts expanded with the universe then the whole distance the light had to travel expanded. Either that expansion happens with less than light speed and the distance is impossible or it expands faster and the light wouldn't reach us.
Czl2 t1_ix8ze2e wrote
> Either that expansion happens with less than light speed and the distance is impossible or it expands faster and the light wouldn't reach us.
You raise a good point which shows me you are starting to understand.
Consider that the rate of expansion is not constant but accelerating.
As time passes things that are ever closer to us will start to move away from us at the speed of light and what was once visible will no longer be.
The horizon at which the rate of expansion is at light speed is getting closer and closer to us:
https://www.space.com/einstein-gravity-variations-dark-energy
Your happy thought for today is that all you see and know will not end in a 'big crunch' but instead may be torn apart at the fundamental particle level in a 'big rip':
https://en.m.wikipedia.org/wiki/Big_Rip
Do not panic! This is not yet certain as 'heat death' may happen first. I believe only the 'big crunch' ending has been ruled so at least you can be happy about that.
https://en.m.wikipedia.org/wiki/Ultimate_fate_of_the_universe
Hrambert t1_ix74xl9 wrote
Two ants are walking on a rubber band away from each other at the speed of 10 steps per second. So how far apart are they after 10 second? Much more then expected because I was pulling that band.
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redphoenix932 t1_ix6zo82 wrote
Because for awhile the universe inflated faster than light. Space can move as fast as it wants, it’s only things “in” space that have to follow laws.