How do we know that the universe's expansion is accelerating?

[pilot00]

As the subject reads: How do we know that the universe\'s expansion is accelerating?

I mean we all know that it is expanding but how can we know that it is accelerating?

Thanks! //Pilot00

[Agamemnon]

iirc, redshift/doppler effect

[Kryten]

Due to the finite speed of light, the further we look into the universe, the further we look into the past. Objects further away from us (and therefore further in the past) appear to move away from us less rapidly compared to their distance than closer objects do, and the best explanation we have for that is that the expansion of the universe is accelerating.

[vexx32]

Aye, but the limitation of that is that we can only base this assumption on things a fair way back in the past as compared to other things even further back. So, the universe could have stopped expanding (or the rate could have stabilised)last year, for all we know, or anytime over the last few years, or perhaps even further back, and we would not even know.

[bandit4910]

Aye, but the limitation of that is that we can only base this assumption on things a fair way back in the past as compared to other things even further back. So, the universe could have stopped expanding (or the rate could have stabilised)last year, for all we know, or anytime over the last few years, or perhaps even further back, and we would not even know.

This is true.

The speed of light is only 299,792,458 m/s if, the universes expansion rate was dropped we have no way of telling. If the speed of light was infinite then we would probably see everything in the universe.

(Due to Albert Einsteins theory of relativity it is impossible to break this speed, we can send particles 99% of the speed of light but not fully there.)

[what-the]

I personally don\'t believe the expansion is accelerating. If you imagine the universe with just one direction and time with just a handful of particles all at one point. There\'s an explosion and each particle randomly gets different amounts of energy (velocity) then to any particle all the other particles can look like their accelerating but there not.

lets say

x is going 10m/s

y is going 30m/s

z is going 40m/s

a is going 70m/s

b is going 200m/s

Lets say you are z and you look at the other particles at the 5th second relative to z. (Like what we are doing but on an even bigger scale)

50 150 200 350 1000

x <---- y <---- z ----> a ----> b

-100 -50 0 150 650

Your redshift would be (Not an actual measurement)

30 10 30 130

With a random sample it can appear to be accelerating. As the universe is mostly random then it will appear like it\'s accelerating. We have not been observing the universe for long enough to draw an accurate conclusion.

[Ydoow]

From what I understood, they measured the distance between quasars (or some type of star) which have very regular luminescence.

They can use the received luminescence to figure how far away they are from Earth, and the further away we look out, the more distant these quasars get between each other.

[Kryten]

I personally don\'t believe the expansion is accelerating. If you imagine the universe with just one direction and time with just a handful of particles all at one point...

That would only apply if we\'d only measured a \'handful\' of objects; when you have sample sizes in the thousands or tens of thousands, this kind of random distribution doesn\'t affect the overall result much, if at all.