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Alternate Theories for the Expansion of the Universe

-- | November 15, 2015

Question(s): I have three related questions:

The redshift of objects indicates that the farther away they are, the faster they’re moving, but wasn’t the observed light emitted millions of years ago, when the object wasn’t so far away? How do we know what velocity it’s moving at now, or if it’s even there? Have we measured the velocities of known objects over ‘long’ periods of time to see if their velocities are changing, either speeding up or slowing down?
Rather than a ‘big bang’ with the Universe being created and expanding into nothing, isn’t it possible that it was a ‘big bubble’ similar to nucleate boiling, and that we are surrounded by ‘stuff’ into which we’re expanding?
If we are expanding into stuff, couldn’t the cosmic background radiation be coming at us from outside the boundaries of our Universe? Could ‘dark’ energy and matter be external also? — Larry

Answer(s):

You are correct in that the light emitted from distant objects that we observe today was emitted from the distant object in the past, its speed in getting to us limited by the speed of light. We do not have a way to measure an object’s velocity “now”, but we can measure the velocities of objects at a range of distances from us. This allows us to sample the expansion rate of the universe at a range of distances, and therefore measure the speed-up or slow-down of the universe’s expansion.
The suggestion that the universe is expanding into other “stuff”, like any alternate theory of the expansion of the universe, requires a way to test its observables. This is the problem with most alternate theories. How would you measure the “stuff” into which our universe is expanding? I don’t believe that it is possible to measure the material into which we might be expanding, so this alternate theory really is not viable.
I am not aware of any observations which would allow for the cosmic microwave background and dark energy to be derived from an external body of matter. At this point, this would be a theory which lacks observations to support it.

Jeff Mangum

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