Hubble Tension Part 2: Baryon Acoustic Oscillations
There is an introduction to the nature of the “Hubble tension” in the first part of this article, which covers measurements based on the distance ladder (see https://physbang.com/2026/07/28/hubble-tension-part-1-the-distance-ladder/). This article looks at how the Cosmic Microwave Background (CMB) can be used to calculate the expansion of the Universe – and therefore the Hubble constant. But first it is useful to…
Read moreHubble Tension Part 1: The Distance Ladder
The term “Hubble tension” refers to discrepancies in the value of the Hubble constant, which in turn indicates the rate of expansion of the Universe. In particular, the “tension” arises because two different techniques for calculating the constant give significantly different values. For a brief introduction to the Hubble constant, see https://physbang.com/2026/04/26/red-shift-and-the-age-of-the-universe/ or NASA’s summary at https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/hubble-cosmological-redshift/. Although the constant…
Read moreExponential changes
Imagine an empty tube train (metro, if you prefer) pulling into a crowded station. When the doors open, people surge forward and the carriage starts to fill very quickly. As the number of people in the carriage increases, the number of remaining spaces decreases and the rate at which further people can board also decreases. After a while, the carriage…
Read moreHow do electric cells generate a current?
We take for granted the fact that an electric cell (or battery) will cause a current to flow through an external circuit. The current is often discussed in terms of a flow of electrons (like water through a pipe) or energy transferred between adjacent electrons (like a row of dominoes falling onto each other). It might even be explained in…
Read moreAnswers to some of physics’ biggest mysteries
Exam season is over so this seems like a good time to admit that physicists don’t know all the answers – and don’t even always agree on which of the available answers is best. The two biggest areas of disagreement are cosmology and quantum mechanics. For example; Everybody is entitled to a view on such matters but to determine the…
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