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Please correct me If I'm wrong but does not the BB only refers to our light speed limited observable Universe (OU) from our home position?

Also it is estimated that the Cosmos is minimum 250 times the size of our OU.

Why should our small patch in the cosmos be given a birthday and not being instead part of a much older and already existing cosmos really escapes me?

What is the evidence for such an argument about our OU having a birthday?

Wouldn't it be more logical to seek for a BB date for the Cosmos instead?

Qmechanic
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Markoul11
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1 Answers1

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The evidence for our observable Universe having a birthday are the commonly mentioned ones.

  • Redshift of galaxies vs distance shows the universe is expanding
  • Cosmic Microwave Background matches what we would expect from an early hot universe that has expanded and cooled
  • The observed mixture of elements matches predictions of nucleosynthesis
  • Differences on looking back in time (E.G. quasars) show a steady state universe is unlikely.

There are reasons for thinking the rest of the cosmos shares this birthday.

  • The laws of physics are consistent across the observable universe as far as we can tell. This includes things like General Relativity.
  • It is a reasonable extrapolation to assume they apply to the rest of the universe as well. We certainly see no boundary beyond which we expect the laws to change.
  • As your link points out, from what we see the best bet is that the larger universe is flat. On the largest scales, the universe is uniform. This makes it reasonable that conditions elsewhere are much like conditions here.

On the other hand, there are speculations that things do change beyond what we can see. The Multiverse, Science or Science Fiction? | Sean Carroll

mmesser314
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