Recent content by Jaime Rudas

As a curious fact, it seems that Hubble never actually called it that. The earliest appearances of the term 'Hubble constant' that I have found are from 1952 in Hermann Bondi's book Cosmology.

Yes, the Hubble constant ##H_0## is constant in space, not in time.

Actually, that constant wasn't just 'invented' 100 years ago; it's a direct consequence of applying general relativity to a homogeneous and isotropic universe, as Lemaître demonstrated in 1927. Not 'insisting' on it would imply not insisting on general relativity, or not insisting on the...

Yes, when we talk about cosmological distances, we generally refer to space-like separations between comoving objects.

Another way to visualize what 70 km/s/Mpc is equivalent to is to show that something expanding at that rate will double its size in about 14 billion years.

Yes, but to measure the Hubble constant, you need to know the distances.

Redshift tells you the distance only if you already know the rate at which the universe is expanding.

If the Earth were expanding at the same rate as the current expansion of the universe, then two cities 1000 kilometers apart (Paris and Madrid, for example) would move 7 millimeters apart every 100 years, while two cities 2000 kilometers apart (Budapest and Madrid, for example) would move 14...

I believe that for a model of reality to be predictive, its fundamental principles must correspond to reality and its mathematical development must be correct. However, simply having correct mathematical development will not make a model predictive if its foundations don't correspond to reality.

Frenkel says (4:32): "Mathematics does not come to us from physical reality." Is there really anything that could not come from physical reality?

I only joined the forum recently, so I couldn't say if it's more or less moderate than in the past. However, I believe that strict moderation is one of the keys to PF's success. That said, I also think that some aspects of moderation can be frustrating, such as the limited opportunity to discuss...

The word 'ether' has had several meanings throughout the history of science. For example, regarding your question, look at what Einstein wrote in his book 'Sidelights on Relativity' (1920):

Sound doesn't propagate through the unobtainium.

Perhaps one of the first to analyze this situation was Paul Ehrenfest in his 1909 paper "Uniform rotation of rigid bodies and the theory of relativity" which is why it is now called the Ehrenfest paradox.

Yes, but that's what happens with all unsolved problems in science (inflation is one of them). The way science advances is precisely by devising hypotheses about their solution and testing them experimentally. Since these are still unresolved problems, it is perfectly logical that there is no...