The evidence that space is expanding is pretty compelling.
We also observe that this expansion is accelerating. Why? Who knows? it has been labeled Dark Energy as a place holder.
The current thinking seems to be that Space and time are pretty closely tied together: spacetime is “a thing.”
What if spacetime is conserved…as space expands, time somehow shrinks?
Could it be the case that time isn’t constant? If time were somehow contracting as space expands, wouldn’t this be perceived as an accelerating expansion?
If time is changing could there be any way to detect it?
Well, time isn’t a constant. Different frames of reference experience time differently.
If you’re asking if the whole universe is experiencing random changes in time then how could we know? If the clock you’re using to measure time slows down with all the other reactions in the universe, and your brain slowed as well, it would seem exactly the same as if it never changed.
But the problem with that is how do the time changes propagate across the whole universe simultaneously?
Could we tell if time is not continuous and not ordered? By that I mean that if you took a film reel, and cut it up frame by frame, and shuffled the frames around, would the people in the movie even notice? “Film” in this case being time, and the “frames” are “moments” or “instants” or whatever you might call a discrete point in time.
If time were not continuous, we would not see spectrum lines correctly. The current “redshift” (universe expansion) would be illusory or exaggerated. Current observations show a regular spectrum, but the lines are red-shifted with distance. If time passed irregularly, spectrum lines from distant stars and galaxies would be shifting up and down.
I would say that we can be fairly sure that it is constant, because there are so many different technologies that keep time, and they allremain in synchronization. Atomic clocks, spring wound clocks, water clocks, sundials, penculums, heartbeat, they all continue to run in synchronicity. That is a strong indicator, to me, that all plysical events take place within the same time frame. If I understand the question correctly.
Maybe I’m just missing the whole point, folks. If time sped up or slowed down, wouldn’t our mechanical timepieces show us what happened? I mean the old-school, spring-driven timepieces. They’re not tied to time, in the sense that they’d synchronize with the new flow of time. They’re just engineered, with counterweights and escapement, to match the rate of time flow that existed when they were designed.
They’re unable to synchronize to GMT, like the gee-whiz clock in my living room does.
Right, but in the “movie”, the redshift behaves like we’d expect. I’m asking if the movie is cut up and rearranged, if we, the people, things and phenomena inside it, could tell?
My motivation here is entropy. Its vastly more probable that entropy will be higher in the future than it is now. But by the same reasoning, it should be vastly higher in the past, too, and we don’t observe that. So I wonder if the universe is some sort of entropy “soup” that occasionally, randomly jumps to a much lower entropy state for an instant. And then our lives are just assembled in an ordered way from those random snapshots of less entropy. Like reassembling a movie from its jumbled frames.
That is not correct. Time is not constant, as predicted by Einstein and the twins paradox. In fact, GPS satellites must take into account of the effect in order to give us accurate readings.
Wouldn’t every examination of data over time show these sudden jumps? I don’t understand how any smooth changes would ever be possible. We have data from every time back to the beginning of matter. How could something not stand out in that?
I have nothing to add to this besides the fact that this is such amazing stuff. Honestly, the physical world around us is full of so much wonder and chances for discovery.
I am awed by natural science every time I read something like this.
But what causes a spring to drive a watch? A physical process. If time speeded up, then the physical process that causes the watch to move the gear would speed up. If it takes a second for a pendulum to swing, it takes 1 second. What would it mean if 1 second of time took 2 seconds? A second is defined as the amount of time it takes some rubidium atom to vibrate a gazillion times. That’s how atomic clocks work. A second could be defined as the amount of time it takes a given pendulum of a given characteristics to swing once. But if time slowed down, the pendulum would slow and the rubidium atom would slow and our brains would slow, and it would seem to us that everything would take the same amount of time.
And when time does slow via relativity, this is what happens. All physical processes are affected.
Nothing is in the same frame of reference. Even the end of a clock’s minute hand is in a different frame of reference from the axle about which it rotates.
If the expansion of the universe is accelerating, how do we know it is accelerating? What’s our frame of reference? How do we know that our frame(s) of reference are not decelerating giving the appearance of an accelerating expansion?
Is this what the OP is asking? If not, it’s what I’m wondering.
But if our local area were slowing down and the rest of the universe was moving at a constant rate, then why does it seem that the expansion of the universe is isotropic? That is, everything seems to be moving away from us with the same Hubble constant no matter where we look. If our little part of the universe were slowing down or moving in some idiosyncratic way then that wouldn’t be true.
As a sidebar, I remember once reading about the Big Crunch, and the theory that if the universe were to recede again, time would reverse. The article then went on to say that this would lead to a weird universe of trees getting smaller, eggshells reforming etc.
I assumed that this was nonsense, and that in such a hypothetical, brain processes would also go in reverse, and for all we know time is reversing right now.
But two questions:
Was my guess right?
Why would matter all falling together cause time to go backwards?