Depending on where we look, the universe is expanding at different rates. Now, scientists using the James Webb and Hubble space telescopes have confirmed that the observation is not down to a measurement error.
As I understand it, there are two measures of cosmic distance/expansion rate in which we are pretty confident.
One is using supernovas as a measure. Since one kind of supernova has very particular characteristics, it is easy to calculate the distance. It is like knowing that everyone has the same kind of candle, if you see a bunch of lights around you, you could make certain assumptions about how far they are from you by how bright they are. Also, with more precise measurements, we can use the doppler effect to know how fast they are moving. We have observed the area around or Galaxy and have come up with a very precise measurement for how fast the universe is expanding.
The other measurement is by looking at the cosmic wave background. This is the “first” thing we are able to see after the big bang. I don’t really understand the details of this one, but scientists have also been able to calculate the expansion rate of the universe very accurately with this radiation.
As we have done more experiments to measure these two numbers, instead of converging on the same number, the results are actually diverging. Recent results have even made it so the error bars no longer overlap.
So, we have some big questions -
Are our measurements wrong? There are no strong candidates for alternative understandings of how we measure things, so we don’t really know how.
Are the expansion rates at the beginning of the universe and current times different? Maybe, but again, we don’t have any theories for why.
Does the Universe expand at different rates in different places? Maybe, but again, we don’t have any strong candidates that we can test.
All of this is called the Hubble Tension. It is probably one of the biggest questions in cosmology currently.
As I understand it, there are two measures of cosmic distance/expansion rate in which we are pretty confident.
One is using supernovas as a measure. Since one kind of supernova has very particular characteristics, it is easy to calculate the distance. It is like knowing that everyone has the same kind of candle, if you see a bunch of lights around you, you could make certain assumptions about how far they are from you by how bright they are. Also, with more precise measurements, we can use the doppler effect to know how fast they are moving. We have observed the area around or Galaxy and have come up with a very precise measurement for how fast the universe is expanding.
The other measurement is by looking at the cosmic wave background. This is the “first” thing we are able to see after the big bang. I don’t really understand the details of this one, but scientists have also been able to calculate the expansion rate of the universe very accurately with this radiation.
As we have done more experiments to measure these two numbers, instead of converging on the same number, the results are actually diverging. Recent results have even made it so the error bars no longer overlap.
So, we have some big questions -
All of this is called the Hubble Tension. It is probably one of the biggest questions in cosmology currently.
Thanks this is both an uncomfortable and exciting thing to read.