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Measuring the expansion of the universe -

Measuring the expansion of the universe –

As astronomer Phil Plait points out in his blog bad astronomerEverything seems to indicate that galaxies are moving away from us. Scientists also noticed that the further away they were, the faster they went. By dividing the speed at which a galaxy is moving away from us, we can also measure the Hubble constant, which tells us how fast the universe is expanding.

Two methods allow calculating this constant. The first is to look at the ends of the universe by studying cosmic background radiation Which corresponds to the electromagnetic radiation emitted by the Big Bang. The second is more interested in objects close to us, galaxies.

The advantage of having two methods is that one measures what was happening in the early universe while the other tells us about the more recent expansion. Problem: The value of the Hubble constant varies depending on the method used.

galaxies and earth

However, measuring the distance of galaxies is not easy. In general, astronomers trust some existing stars whose brilliance is well known. The Cephedes Especially useful because its brightness varies very regularly. Since the brightness of a star decreases as one moves away from it, one can infer its distance from Earth by comparing the intensity of the observed light with that expected.

According to the University of Chicago astronomer, Wendy FriedmanHowever, this method will not be as accurate as thinking. I came to this conclusion by comparing it to another method that uses a different type of star, red giants.

According to his findings, these two very similar methods give somewhat similar results for the velocities of galaxies near Earth, but the data diverge for distant galaxies. Thus, these two methods will not be developed and will not give a fair idea of ​​the Hubble constant, according to the researcher’s estimates.

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Physics question?

The discrepancies between the measurements of the Hubble constant are a major problem for astronomers. In fact, they should be able to determine whether it is the result of a technical error or a real physical phenomenon. Indeed, in the latter case, it could mean that the expansion of the universe is accelerating and that the current laws of physics must be reconsidered.

However, according to Wendy Freedman, before we get to that, it’s best to make sure we can trust our measuring tools. The astronomer also asserts that cosmic radiation measurements are much more accurate than those obtained by measuring the distances of galaxies. So it will be important to refine these methods before jumping to conclusions.

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