The universe got its start billions of years ago in the Big Bang. Since then, it has been continuously expanding. These concepts are generally accepted by virtually all scientists.
The question, however, is just how fast the universe is expanding. The rate at which this occurs is known as the Hubble constant, but when measurements are taken in various ways, the results are not actually constant. This means that either the measurements are wrong, or our understanding of the universe is wrong, or both.
There are two main options when figuring out what the rate of expansion for the universe actually is. First, measurements of the cosmic microwave background (CMB) can be taken. The next option is to measure the distances between galaxies and some time later, take the measurements again. This can give you the distance that they traveled away from each other, and therefore the rate of expansion.
If you use the first option, the results will show that the universe is expanding at 67.45 kilometers per second per megaparsec. If you use the second method, however, the result is that the universe is expanding at 72.8 kilometers per second per megaparsec.
Of course, there is a margin of error for both of these methods. Unfortunately, that margin is not large enough, even when combined, to generate an overlap.
The Hubble Space Telescope had long been used to get relatively precise measurements of galaxies, and that is how much of the data was gathered for the second measurement method.
A team led by Nobel laureate Adam Riess has started using measurements from the James Webb Space Telescope to see if they were more accurate and would help to solve this ‘Hubble Tension.’
Unfortunately, that was not the case. The measurements with the JWST show that the universe is expanding at 72.6 kilometers per second per megaparsec, which is just slightly less than what was found with the Hubble Telescope.
Professor Riess talked about this discrepancy in a statement, saying:
“The discrepancy between the observed expansion rate of the universe and the predictions of the standard model suggests that our understanding of the universe may be incomplete. With two NASA flagship telescopes now confirming each other’s findings, we must take this [Hubble tension] problem very seriously—it’s a challenge but also an incredible opportunity to learn more about our universe.”
Clearly more data points are needed and more research on the topic will hopefully find ways to get a more accurate understanding of the expansion of our universe.
The Hubble Constant isn’t as constant as it seems.
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