heehaw wrote:It looks very much as if the Universe is infinite in size, from the microwave background results. If that is so, there are infinitely many Earth-like planets, including infinitely many on which there is a US election underway at the moment. If the Universe is BIG but is not infinite, then we don't know how many Earth-like planets there are bearing life.
How does the nature of the microwave background argue for an infinite sized universe? As we lack any observations outside the observable universe, and our cosmological theory is very incomplete in some respects, I'd suggest that we really have no idea at all beyond speculation whether the Universe itself is finite or infinite.
The way I understand it, Chris, the microwave background argues for a flat, ever-expanding, Lambda Cold Dark Matter universe. Such a universe is at least "expanding into" infinity. I also think it has not absolutely been proven that the universe is actually open and ever-expanding. A universe that is "just" closed is not so different, geometrically speaking, from an open, flat one. Of course, with the acceleration of the universe, it becomes much harder to argue that the universe might be closed.
So the universe is probably open and expanding into infinity. But that in itself doesn't mean that it must contain an infinite number of galaxies, solar systems or Earths. Such an idea belongs to the Steady State theory of the universe, which indeed requires that the amount of matter, and therefore probably also the number of objects in the universe, must grow as the universe grows bigger. But the Steady State model proposes that the universe remains unchanging forever, except that it keeps growing in size, and that idea is not accepted by the overwhelming majority of today's astronomers.
heehaw wrote:It looks very much as if the Universe is infinite in size, from the microwave background results. If that is so, there are infinitely many Earth-like planets, including infinitely many on which there is a US election underway at the moment. If the Universe is BIG but is not infinite, then we don't know how many Earth-like planets there are bearing life.
How does the nature of the microwave background argue for an infinite sized universe? As we lack any observations outside the observable universe, and our cosmological theory is very incomplete in some respects, I'd suggest that we really have no idea at all beyond speculation whether the Universe itself is finite or infinite.
The way I understand it, Chris, the microwave background argues for a flat, ever-expanding, Lambda Cold Dark Matter universe. Such a universe is at least "expanding into" infinity.
Yes, flat. Yes, ever-expanding. But such a universe need not be infinite, and there's no concept in the LCDM model of anything the Universe is "expanding into". To be clear, a flat universe does not imply an infinite universe for all possible topologies (and the actual topology is unknown).
In the APOD illustration, there are streamers blasting away from the planet in the opposite direction of Rho Cancri.
If you were present on the surface of the planet, and on the dark side, it would probably appear in every direction you looked that there was a wall of glowing gas extending up from the horizon.
This probably gives the "Flat Cancri 55 e" advocates a much stronger argument than their counterparts on Earth!
The person who created the featured video, Robert Hurt, has now identified himself. I have therefore added his name and affiliation to the credits. - RJN
