Just been on a space video kick lately and am pretty ignorant about most of it.
One thing I see a lot of these videos saying is that the expansion of the universe seemed to be slowing down until around 5 billion years ago.
How can we tell that it was slowing down 5 billion years ago if it started speeding up afterwords? Like how do they map out the universe and say “yeah it was slowing down until this time.”
Is it just a theory or is this something commonly accepted as fact? Appreciate any info and thanks! 🙂
In: 5
We can do this by looking at the light of distant stars and the characteristics of that light. Scientists can measure the red shift caused by universal expansion and the spectra of the light from given stars and calculate the speed with which the appear to be moving away from us. We know the characteristics of different stars based on other observation, hydrogen and helium emit in different ranges of EM. When redshifted they will appear at different wavelengths than they would if you measured them closer to the source so we can calculate the shift. Other related measurements help give us more information.
But it’s not just the observations that neuter, we also have models based on physics that tell us what we should expect to see. When the observations match those we can be more confident the models are right and those models also show various phases of expansion.
So we predict behavior based on models, confirm or refine the models based on observation, wash rinse and repeat, getting more and more accurate understanding of cosmology over time.
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