and how do they differentiate between a different rate of expansion and the rate of expansion just changing?
In: Physics
We have different ways of measuring the same quantity.
Some come from using something called the “distance ladder” where we measure different objects at different distances and can calibrate our rulers from that. This can then be used in conjunction with measuring the redshift to get the expansion rate. These give larger values.
Others come from using the “CMB” or Cosmic Microwave Background, where we take some information we have from that early universe and can translate that into a value for the expansion of the universe. These give smaller values.
It’s unclear why they are different at this moment. It’s only been in the last 5-10 years that we were able to be precise enough to know that they were different in the first place. Before that, we’ve been able to just ignore it. This is *the question* in modern Cosmology. Some people believe that it’s coming from issues with our measurements of the CMB temperature, but it’s not certain yet. Others think there’s some unknown bias in the distance ladder, so neither method is immune to scrutiny.
This is actually my area of research at the moment, and I’ve just spent a good year and a half getting simulations to show that one proposed solution won’t work.
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