Expansion of the Universe

[Mordeth]

Hi All,

I am trying to understand how we can show that the expansion of the universe is accelerating.  I understand that one way is to use data taken from observing Type 1a supernovae due to their standard intrinsic luminosity.   This then allows us to calculate luminosity distance and redshift, and from there calculate a ratio that apparently shows it to be non-linear over many samples taken at large distances.  Wouldn't this just show that the expansion rate is changing?  How do we specifically know it is accelerating?  Have we ever observed a ratio that suggests the opposite?

What I also do not understand is how we can know what the size of the universe was at the time the light was emitted.  Does the redshift itself that we observe give us a clue as to the size of the universe at the time the light was emitted?

And also, is there a possibility that the effect we are seeing is simply an illusion due to relative movement?  Or could space be accelerating in some areas and not accelerating in others?

Thanks for any insight.  

[beecee]

8 hours ago, Mordeth said:

Hi All,

I am trying to understand how we can show that the expansion of the universe is accelerating.  I understand that one way is to use data taken from observing Type 1a supernovae due to their standard intrinsic luminosity.   This then allows us to calculate luminosity distance and redshift, and from there calculate a ratio that apparently shows it to be non-linear over many samples taken at large distances.  Wouldn't this just show that the expansion rate is changing?  How do we specifically know it is accelerating?  Have we ever observed a ratio that suggests the opposite?

What I also do not understand is how we can know what the size of the universe was at the time the light was emitted.  Does the redshift itself that we observe give us a clue as to the size of the universe at the time the light was emitted?

https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe

 

Quote

 

nd also, is there a possibility that the effect we are seeing is simply an illusion due to relative movement?  Or could space be accelerating in some areas and not accelerating in others?

Thanks for any insight.

 

The Universe is only seen to be accelerating in its expansion rate over larger scales.....Over smaller scales [our local group of galaxies and even beyond] gravity overcomes the expansion rate.

Edited November 2, 2018 by beecee

[Conjurer]

On 11/1/2018 at 6:18 PM, Mordeth said:

 Wouldn't this just show that the expansion rate is changing?  How do we specifically know it is accelerating?  Have we ever observed a ratio that suggests the opposite?

The amount of red-shift increases the further out the galaxies are from where it is coming from.  The type 1a supernova is assumed to emit the same wavelength of light, so then they can know the distance the star is away from us from how much that light is red-shifted from what they think it should be from that explosion. 

The further out the supernova in the galaxy is away from us, the faster it would have had to go to be at that further distance.  When they assume everything use to be in one location at the start of the Big Bang by trying to rewind the clock on their movement, they find that everything would have had always have been accelerating in order for it to be in the location it is now from that type of event.  Then it would have always had to have been accelerating at an exponential speed which would look the same as a parabolic curve.  Then this rate of acceleration has not always fit this type of graph exactly, and there had to be slight increases more recently and at the time of half of the age of the universe in order for it to come out right to what they observe in the sky.

On 11/1/2018 at 6:18 PM, Mordeth said:

What I also do not understand is how we can know what the size of the universe was at the time the light was emitted.  Does the redshift itself that we observe give us a clue as to the size of the universe at the time the light was emitted?

 The distance stars are calculated to be away from us is measured in light years, and one light year is the time it takes for light to travel in one year.  Then the distance it is away from us is the same as where it was that many years ago.  Then how many light years it is away from us is calculated from the amount of red-shift the light has from it.

 

On 11/1/2018 at 6:18 PM, Mordeth said:

And also, is there a possibility that the effect we are seeing is simply an illusion due to relative movement?  Or could space be accelerating in some areas and not accelerating in others?

It is believed that the amount of red-shift is caused by spacetime itself actually stretching out between galaxies.  Then the waves of the light gets stretched out and red-shifted as it travels through that space which is stretching out.  The amount of expansion is really uniform in all directions, and it is more uniform than any other type of explosion known to exist on a total scale.

Edited November 7, 2018 by Conjurer