Viswanathan K's Thoughts

Remember the basis for coming up with the idea of dark energy? It was the accelerating universe. And how did Perlmutter and Riess come to the conclusion that the expansion is accelerating? Physicist Sabine Hossenfelder explains . There’s a certain class of supernovae, the type Ia, for which we know the energy emitted over time. The farther away it is, the dimmer is appears. Thus, from its brightness, one can infer the distance. In addition, the farther away it is, the longer it took to reach us. So indirectly, from its brightness, one can calculate how long back it occurred. At the same time, one can determine its color. Just as the sound of a moving ambulance get shriller as it comes closer, the observed color of the supernova changes since it (and space itself) are moving away from us. The color can thus be used to infer the rate at which space is moving away. Combine the above two points (time of the supernova v/s rate of expansion) for multiple supernovae at differen...

Dark matter. Dark energy. They are supposed to make up most of the universe (20% and 75% respectively), leaving just a tiny 5% to the “normal” matter and energy we humans are made of and deal with on a day-to-day basis. But what are dark matter and dark energy? Physicist Sabine Hossenfelder answers . Let’s take “dark matter” first. Based on the amount of matter we can see either visually or via our detectors that use signals other than visible light, the stars on the edges of all spinning galaxies should get thrown into outer space. On a bigger scale, galaxies should never have formed in the first place. So what is this force that keeps stars and galaxies from flying off? The answer: gravity. Wait a minute, didn’t we just say that there isn’t enough perceivable matter to produce the needed gravitational force? Yes, but the key word is “perceivable”. The objects producing the “missing” gravity are not perceivable, so they’re called “dark matter”. Not “dark” as in sucking up ligh...