DanishDynamite

2007-Sep-11, 07:57 PM

I've just realized a very strange coincidence after reading a few threads here. The coincidence is so strange that I'm quite certain it is no coincidence and that I just haven't understood how certain concepts depend on each other.

Here's the coincidence:

The Hubble constant is a measure of the expansion rate of our Universe. It assumes that the further away something is from something else (cosmologically speaking), the faster they will move apart from each other and do so in a linear fashion. I.e if the Hubble constant was around 70 km/s/megaparsec (which it is) this would mean that something 1 megaparsec away from us would be moving away from us at about 70 km/s. And something 2 megaparsecs away from us would be moving away from us at about 140 km/s. Etc.

Fine.

Now, it would seem to me that any estimates of the value of this constant would not necessarily make use of the age of the Universe as part of the calculation of this value nor as part of the method of obtaining this value. Perhaps this is wrong, but I don't see how.

This is observation no. 1.

The age of the Universe is another interesting bit of knowledge. I'm not sure what evidence exists for this age, but I presume at least some of it is not dependent on the value of the Hubble constant. Is this correct?

This is observation no. 2.

If this is correct, then there is the very odd coincidence which I mentioned at the beginning. And the coincidence is this:

If the age of the Universe is around 14 billion years, then any photon we detect today could at most have traveled for 14 billion years, and hence at most have traveled 14 billion light-years or around 4,300 megaparsecs. Assuming a Hubble constant of 70 km/s/megaparsec, how fast would something be traveling away from us (according to Hubble) at this distance of 4,300 megaparsecs? Well, it would be traveling away from us at around 70 km/s/megaparsec X 4,300 megaparsecs = 301,000 km/s.

Anyone recognize that number?

That's the speed of light!

Surely this is not a coincidence?

Here's the coincidence:

The Hubble constant is a measure of the expansion rate of our Universe. It assumes that the further away something is from something else (cosmologically speaking), the faster they will move apart from each other and do so in a linear fashion. I.e if the Hubble constant was around 70 km/s/megaparsec (which it is) this would mean that something 1 megaparsec away from us would be moving away from us at about 70 km/s. And something 2 megaparsecs away from us would be moving away from us at about 140 km/s. Etc.

Fine.

Now, it would seem to me that any estimates of the value of this constant would not necessarily make use of the age of the Universe as part of the calculation of this value nor as part of the method of obtaining this value. Perhaps this is wrong, but I don't see how.

This is observation no. 1.

The age of the Universe is another interesting bit of knowledge. I'm not sure what evidence exists for this age, but I presume at least some of it is not dependent on the value of the Hubble constant. Is this correct?

This is observation no. 2.

If this is correct, then there is the very odd coincidence which I mentioned at the beginning. And the coincidence is this:

If the age of the Universe is around 14 billion years, then any photon we detect today could at most have traveled for 14 billion years, and hence at most have traveled 14 billion light-years or around 4,300 megaparsecs. Assuming a Hubble constant of 70 km/s/megaparsec, how fast would something be traveling away from us (according to Hubble) at this distance of 4,300 megaparsecs? Well, it would be traveling away from us at around 70 km/s/megaparsec X 4,300 megaparsecs = 301,000 km/s.

Anyone recognize that number?

That's the speed of light!

Surely this is not a coincidence?