Is new space(time?) being created as the Universe expands, or does the existing spacetime just get stretched?
If it just gets stretched, why do galaxies move along with the expansion instead of just getting smeared (like a drawing on an inflatable balloon)?
Answer
Since the second part of your question is a duplicate I'll address just the first part. however I suspect you're going to be disappointed because my answer is that your question doesn't have an answer.
The problem is that spacetime isn't an object and isn't being stretched. We're all used to seeing spacetime modelled as a rubber sheet, but while this can be a useful analogy for beginners it's misleading if you stretch it too far. In general relativity spacetime is a mathematical structure not a physical object. It's a combination of a manifold and a metric. At the risk of oversimplifying, the manifold determines the dimensionality and the topology, and the metric allows us to calculate distances.
We normally approximate our universe with the FLRW metric, and one of the features of this metric is that it's time dependant. Specifically, if we use the metric to calculate the distance between two comoving points we find that the distance we calculate increases with time. This is why we say the universe is expanding. However nothing is being stretched or created in anything like the usual meaning of those words.
No comments:
Post a Comment