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from the expanding-like-a-waistline-on-Thanksgiving dept.
Arthur T Knackerbracket has found the following story:
Reproduceability is key to science. A one-time “eureka!” could be the first step in a paradigm shift — or it could be a fluke. It’s the second, third, and hundredth measurements that put theories to the test.
That’s why recent measurements of the universe’s expansion have piqued interest. Even though astronomers have applied multiple methods relying on completely different physics, they’re still getting similar results: Today’s universe appears to be expanding faster than what’s expected based on measurements of the early universe. Can systematic errors explain this discrepancy? Or are new physics required?
Now Wendy Freedman (University of Chicago) and colleagues have posted a new, "middle-of-the-road" measurement on the astronomy preprint arXiv, adding a twist to the ongoing debate. The study will appear in the Astrophysical Journal.
(Score: 2) by Common Joe on Friday September 20 2019, @10:08AM (3 children)
Actually, you can see that yourself. Google the question "How big is the universe?" It will come back with 93 billion light years in diameter... so 46.5 billion light year radius. (That's the known universe we can see.) Then google "How old is the universe?" It will come back 13.8 billion years. If light travels at... well, the speed of light, then how does star light travel 46.5 / 93 billion light years in 13.8 billion years? I think that's what's meant by the inflationary period went faster than light. (I'm not a physicist.)
(Score: 2) by hendrikboom on Friday September 20 2019, @02:00PM (2 children)
I have always wondered about that. Clearly that remote matter would not be observable, at least, not for another 46.5 billion years.
But I wonder how relativistic distance-dilation is taken into account when calculating the 46.5 billion light-years. Is it indeed taken into account? Or is it compensated for?
I'm often confused when reading a popularization of science, trying to figure out what the original science was before popularization. Translating modern physics into everyday terms is quite misleading, because everyday terminology has assumptions built into it that are quite at odds with the way science has discovered the world really works.
I do know that relativistic velocities don't add linearly, and I have a sneaky suspicion that these "faster than light" claims rest on linear addition of velocities.
Take some far-off galaxy, departing from us at the 90% of the speed of light. Now consider another galaxy, even farther out, that's departing from the far-off galaxy, relative to the far-off galaxy, ad 90% of the speed of light. It's commonly considered that addition of velocities should make the farther-off galaxy recede from us at 180% of the speed of light. But that's not how addition of velocities works. Relativistically, it's nonlinear, not naively additive, resulting in a total velocity that's still lower then the speed of light.
But that's special relativity. But I admit I don't know what measuring velocities at a distance means when using general relativity. For example, the Doppler shift would seem to indicate that photons lose energy when traveling across an expanding cosmos. But I think reality must be more complicated because that would seem to violate conservation of energy.
-- hendrik
(Score: 2) by Common Joe on Friday September 20 2019, @03:58PM (1 child)
Disclaimer: I'm not a physicist. I only pretend to be one from time to time and I do a horrible job at it.
It is compensated for, but how they do it exactly is beyond my knowledge.
My understanding is that mass can be accelerated to velocities up to the speed of light. There are no rules against traveling faster than the speed of light. You just can't accelerate beyond the speed of light. If you can make the jump from one speed to another without going in between (something currently beyond our science), then it is (theoretically) possible to travel faster.
A long time ago, I calculated the relativistic equations. I suck at it, but I did it. It does work, but I can't explain it as well as videos on Youtube. I picked a random one, but it's good enough: https://www.youtube.com/watch?v=rVzDP8SMhPo [youtube.com]
It boils down to this: in your example, time and length are perceived differently by each galaxy. It's that simple (and that complex).
Another way to look at it: From our perspective: the faster an object goes, the more energy it will absorb to go faster. Let's say we add X energy to get it to accelerate to 10% the speed of light. Now, the more energy it absorbs, the heavier it will become. (E= mc2, right?) If we add X energy again, it will only accelerate 9%. If we add X energy again, it will accelerate only 7%. (My numbers are not accurate, but the idea is.) From the objects perspective, we keep giving it less and less energy. So, the first time, we give it X energy. The next time, we give it only 90% energy. The next time, it's 75% energy. (Again, numbers are not accurate, but the idea is.)
Hope this helps. It took me a long time before I got it. They have some good videos out there these days that explain relativity decently enough which I didn't have when I was younger. I don't have enough time to track them down right now, though.
(Score: 2) by hendrikboom on Saturday September 21 2019, @08:21PM
Exactly!