universe death

wad · Jul 11th 2017, 05:07 PM

Whether we regard the universe as a expanding sphere or the surface of an expanding balloon, as, starting with the beginning of time, all spherical stellar masses in the universe emit photons (electromagnetic energy) in every direction, more than half of all photons are being irreversibly sent outward beyond the edges of the universe - such edges defined the last radii where masses exist. Does this mean that the universe will die from total dispersion of its energy as photons?

topsquark · Jul 11th 2017, 10:00 PM

Originally Posted by wad

Whether we regard the universe as a expanding sphere or the surface of an expanding balloon, as, starting with the beginning of time, all spherical stellar masses in the universe emit photons (electromagnetic energy) in every direction, more than half of all photons are being irreversibly sent outward beyond the edges of the universe - such edges defined the last radii where masses exist. Does this mean that the universe will die from total dispersion of its energy as photons?

You need to be careful talking about "edges" for the Universe. Due to the speed of light and the generally accepted Big Bang model we can only observe phenomena 13.5 billion light years away. (Actually less than that but that's a topic for another time.) So the Universe may not have a boundary.

Now, if photons are leaving our "bubble" then symmetry would seem to demand that any radiation that might leave us then there will also be photons entering from another bubble. Not much evidence for this though, for or against.

There are a lot of possible stages here. I'll skip over the details as I know them (another topic for another time) and say that, yes, unless we have a Big Crunch the Universe will be filled with a radiation field growing ever colder as the Universe keeps expanding.

-Dan

Woody · Jul 12th 2017, 10:17 AM

extrapolating the universal expansion as currently observed,
we can envision a time when the expansion is moving every subatomic particle away from every other subatomic particle at greater than the speed of light.

ChipB · Jul 12th 2017, 11:15 AM

Originally Posted by Woody

extrapolating the universal expansion as currently observed, we can envision a time when the expansion is moving every subatomic particle away from every other subatomic particle at greater than the speed of light.

How do you figure that? You seem to be assuming that Hubble's Constant is constant over time - but it's not. The inverse of Hubble's constant is a reasonable good indicator of the time since the Big Bang, so as the universe ages Hubble's constant gets smaller. When the universe is twice as old as it is now Hubble's Constant will be about half its current value, and the distance to the furthest objects from Earth will be about twice what it they are now, still receeding from earth at close to the speed of light (but not greater than the speed of light).

wad · Jul 12th 2017, 04:07 PM

To use Hubble's "constant" to approximate the age of the universe implies that HC has been unchanged from the beginning (except for the initial period of inflation). How realistic is it to think the expansion rate up to now has been a single value, and what evidence or theory supports the idea that the rate will be increasing or decreasing in the future?

HallsofIvy · Jul 13th 2017, 05:38 AM

Originally Posted by wad

To use Hubble's "constant" to approximate the age of the universe implies that HC has been unchanged from the beginning (except for the initial period of inflation).

No, it doesn't. You only need to have a rough idea of how it has been changing.

How realistic is it to think the expansion rate up to now has been a single value, and what evidence or theory supports the idea that the rate will be increasing or decreasing in the future?

Pmb · Jul 16th 2017, 06:16 AM

Originally Posted by wad

Whether we regard the universe as a expanding sphere or the surface of an expanding balloon, ...

Who'd regard the universe as either of those? The surface of an expanding balloon is merely an analogy to an expanding spatially closed universe.

Originally Posted by wad

as, starting with the beginning of time, all spherical stellar masses in the universe emit photons (electromagnetic energy) in every direction, more than half of all photons are being irreversibly sent outward beyond the edges of the universe - such edges defined the last radii where masses exist. Does this mean that the universe will die from total dispersion of its energy as photons?

No. Not all matter will be converted into photons. Many stars will eventually collapse into objects such as black holes, neutron stars, white dwarfs etc which will just keep cooling. Eventually all matter will come into thermal equilibrium. That's what heat death of the universe is.