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Is the universe expanding? How could you tell? The attempt to answer these questions has tripped up everybody since Hubble and Einstein.

gpderetta 7y ago
Hum, the universe is both predicted and observed to expand.
- BoiledCabbage 7y ago
  > Hum, the universe is both predicted and observed to expand. Or the universe may not be expanding and time could be contracting.
  - ben_w 7y ago
    What does “time contracting” mean?
    - jerf 7y ago
      While I understand the similarity to what BoiledCabbage is saying to whackjob theories, BoiledCabbage is actually referencing real physics discussions that have occured in the past. Specifically, there is the problem of measuring the universe when you don't have anything not in the universe itself to do the measuring with. What if, for instance, the three dimensions aren't all the same size as it seems, but actually, x is five times larger than y or z and everything time things rotate, including all of your measurement apparatus, they actually grow and shrink? How would you detect such a thing? What if as you look out into the universe, all the constants actually shift in a way that time ends up running at a different speed, so instead of an expanding universe and light taking a long time to get to us, instead there is some sense in which the external universe "really is" younger, and the reason we witness ourselves in a bubble of old universe is simply the anthropic principle? These were all very serious questions around the time of relativity being nailed down, especially since one of the implications of relativity is precisely that you don't have any absolute rulers anymore. While overall the scientific consensus is the scientific consensus, the problem still remains to a lesser degree even today. There's a recent paper questioning whether or not the universe's acceleration rate is actually expanding, because they posit a systematic error in our understanding of the standard candle supernovas used to measure it. What if the "standard candle" turns out to be more dependent on the chemical makeup of the stars than was previously understood, which as the universe gets older the stars have more non-hydrogen in them, so as you look to the younger parts of the universe you misjudge how far away they are systematically? Your ruler was bent in a way you didn't realize, so the distances don't work, so it looks like the universe's expansion has been expanding and there must be this "dark energy" that ends up making the majority of the universe, when it could just be a chimera of our inability to reference absolute measurements.

gpderetta 7y ago

Hum, the universe is both predicted and observed to expand.

BoiledCabbage 7y ago
> Hum, the universe is both predicted and observed to expand. Or the universe may not be expanding and time could be contracting.
- ben_w 7y ago
  What does “time contracting” mean?
  - jerf 7y ago
    While I understand the similarity to what BoiledCabbage is saying to whackjob theories, BoiledCabbage is actually referencing real physics discussions that have occured in the past. Specifically, there is the problem of measuring the universe when you don't have anything not in the universe itself to do the measuring with. What if, for instance, the three dimensions aren't all the same size as it seems, but actually, x is five times larger than y or z and everything time things rotate, including all of your measurement apparatus, they actually grow and shrink? How would you detect such a thing? What if as you look out into the universe, all the constants actually shift in a way that time ends up running at a different speed, so instead of an expanding universe and light taking a long time to get to us, instead there is some sense in which the external universe "really is" younger, and the reason we witness ourselves in a bubble of old universe is simply the anthropic principle? These were all very serious questions around the time of relativity being nailed down, especially since one of the implications of relativity is precisely that you don't have any absolute rulers anymore. While overall the scientific consensus is the scientific consensus, the problem still remains to a lesser degree even today. There's a recent paper questioning whether or not the universe's acceleration rate is actually expanding, because they posit a systematic error in our understanding of the standard candle supernovas used to measure it. What if the "standard candle" turns out to be more dependent on the chemical makeup of the stars than was previously understood, which as the universe gets older the stars have more non-hydrogen in them, so as you look to the younger parts of the universe you misjudge how far away they are systematically? Your ruler was bent in a way you didn't realize, so the distances don't work, so it looks like the universe's expansion has been expanding and there must be this "dark energy" that ends up making the majority of the universe, when it could just be a chimera of our inability to reference absolute measurements.