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I am currently reading "Our Mathematical Universe" by Max Tegmark. From the book I learned a couple of things I find startling:
1. The event horizon, beyond which galaxies run away from us faster than light and hence cannot be seen by us, is about 14 billion light years away.
2. Our universe is about 14 billion years old, and hence at the distance of 14 billion light years, we can only "see", with microwaves, the plasma of the Big Bang.
Now, isn't it a strange coincidence that it is 14 billion years / light years in both cases? I see no reason that these figures should be the same.
Also, wouldn't one the following alternatives occur, assuming that the rate of expansion is constant (actually, we now know that it is accelerating, but let us forget that for the sake of argument):
A. The distance to the event horizon (in light years) is greater than the age of our universe (in years). In this case, we cannot see galaxies run away from us with near light speed, even in principle with infrared radiation, because not enough time has elapsed since the Big Bang for galaxies visible to us to obtain such speeds relative to us.
B. The age of our universe (in years) is greater than the distance to the event horizon (in light years). In this case, we cannot "see" the background microwave radiation caused by the Big Bang, becuse the plasma emitting the radiation is beyond the event horizon and hence cannot be seen by us, even as microwaves.
So, we cannot both detect the background radiation and "see" galaxies run away from us by near light speed.
How is this changed if we (correctly) assume that the expansion is accelerating?
1. The event horizon, beyond which galaxies run away from us faster than light and hence cannot be seen by us, is about 14 billion light years away.
2. Our universe is about 14 billion years old, and hence at the distance of 14 billion light years, we can only "see", with microwaves, the plasma of the Big Bang.
Now, isn't it a strange coincidence that it is 14 billion years / light years in both cases? I see no reason that these figures should be the same.
Also, wouldn't one the following alternatives occur, assuming that the rate of expansion is constant (actually, we now know that it is accelerating, but let us forget that for the sake of argument):
A. The distance to the event horizon (in light years) is greater than the age of our universe (in years). In this case, we cannot see galaxies run away from us with near light speed, even in principle with infrared radiation, because not enough time has elapsed since the Big Bang for galaxies visible to us to obtain such speeds relative to us.
B. The age of our universe (in years) is greater than the distance to the event horizon (in light years). In this case, we cannot "see" the background microwave radiation caused by the Big Bang, becuse the plasma emitting the radiation is beyond the event horizon and hence cannot be seen by us, even as microwaves.
So, we cannot both detect the background radiation and "see" galaxies run away from us by near light speed.
How is this changed if we (correctly) assume that the expansion is accelerating?