Skip to content

Tag Archives: cosmology

But what is the Universe expanding into? [Q&A]

It is probably the most common question astronomers encounter: “Fine, you say that the Universe is expanding. OK, I buy that. But what is it expanding into?” There is really no good way to answer this because the correct answer, that it is not expanding into anything, that there is no outside to the Universe, […]

superluminal expansion [Q&A]

Atul of Canara College asks, is it true that the Universe is expanding at a speed greater than light speed? And if so, does that not conflict with Relativity? Yes, but no. And no. Yes, the Universe is expanding, but there is no single speed that characterizes that expansion. However, two objects separated by a […]

H0 [news]

The latest measurement of Hubble’s Constant (Riess et al., 2011, ApJ, 730, 119, 2011; arxiv:1103.2976) — H0 = 73.8 ± 2.4 km s-1 Mpc-1

Dark Energy [Q&A]

Karthik asks, what is Dark Energy? To put it succinctly: I don’t know. At this point, it is just a name given to something that we don’t really understand. We know from looking at the brightness of Type Ia supernovae (which have very predictable intensities, so their apparent brightness is a good tracker of distance) […]

Is Dark Matter matter? [Q&A]

Karthik asks, if we convert some Dark Matter to energy, will that be energy as we know it, or Something Else™? The history of astronomy has been a series of shocks to the ego of mankind, as the importance of our place in the Universe keeps shrinking. First it turned out that the Earth was […]

residue of stars [Q&A]

Vibha (Poornaprajna PU College) and Tilak (SDM College) ask, there is a lot of stuff in the Universe, especially Hydrogen, where did they all come from? How did they form? Hydrogen is easy (well, in a manner of speaking). It is just an electron paired with a proton. A lot of these were produced during […]

Comoving Distance [Q&A]

Atul of Canara College asks, how is it possible that we can see quasars that are 28 billion light years away, when the Universe itself is only 13.7 billions years old? How can light have traveled farther than the Universe has existed? This can happen because the Universe is expanding. Distances to quasars and similar […]

the observable Universe [Q&A]

Supriya of Poornaprajna College asks, what does the Universe look like beyond the limits to our visible Universe? It is a good point to make that the Universe is actually bigger than what we can see. According to the standard cosmological model, in the early stages of the Big Bang, the Universe underwent a rapid […]

little green men [Q&A]

By far the most common question I get asked on astronomy outreach visits is: are there aliens like us somewhere else in the Universe? There are ten billion stars in our Galaxy, and a hundred billion galaxies in the Universe that we can see, and the Universe itself is apparently a couple of hundred times […]

Universal rotation [Q&A]

This question came from a group — why is it that everything we know of seems to rotate, is it because the Universe as a whole is rotating? Can we infer anything about the Universe’s rotation from the fact that everything seems to rotate? Not really. Suppose you begin with a Universe that is filled […]