The problem is in general relativity is that there is no obvious, general and global definition of time dilation. Sure we could try to set up an ontology where Hubble shift is not the result of cosmic expansion, but the result of ‘cosmic time dilation’, however this is not a particularly useful way of viewing things.
Time is an observation of changing events. It doesn’t exist independently of those events. In other words, if nothing was changing, no time would be passing. This is how time can be observed to be speeding up or slowing down, depending on the events it’s tied too. Any particular cesium atom always emits radiation at the same rate. However, that rate can appear to change, depending on the relationship of the observer and the atom.
Time stops at absolute zero.
If I understand correctly, there is also the implication that anything falling into a black hole never quite falls completely into it because time stops for whatever object is falling into it at the last stages. I never quite wrapped my mind around that concept. I don’t know if it is literally trapped forever in suspended animation or if some other process will eventually free it once the black hole goes away or our universe dies. I am not sure anyone knows but it is a scary thought. Theoretical physics can be both fun and terrifying.
Time doesn’t slow down for you. *You *always experience time at 1 sec/sec. People looking in from the outside - i.e. a different frame of reference - see you as slowing down asymptotically as speed or gravity increases. For *you *time continues just as it always has, falling into a black hole or walking across the street. Nothing can stop time for you in your own reference frame.
Most people would agree that there’s never enough time. Thus, while time may not be constant, the lack of it certainly is.
Rip, tie, cut toy man.
So there is your proof of the inconstancy of time. When you get much older, you will discover that there is too much time, and it is a challenge to find ways to fill it.
Back to rhe original question and my response. If it is already known that time (in the Einsteinian relativistic sense) is already proved inconstant, then the OP question is meaningless. Time is not constant, and we can tell. There is no theoretical “could we?” We can. But in the blunt-instrument sense, I stand by my original answer, that time appears to observers within a fixed frame of reference to proceed without any apparent ripples. Because timepieces, within the accuracy tolerances of the device, remain in synch. Sundials don’t suddenly leap ahead a couple of hours according to some astronomical glitch outside our ken. Or at least, they haven’t yet, that we know of.
You have successfully amused me.
Some days, you’ll think, “I wish this day could last forever.”
Another day, you’ll throw up your hands and think, “I’ve had quite enough of this day. Can it just be over, right now?”
Maybe, our need for more time isn’t constant either.
Time does not stop at absolute zero, not that you can get to absolute zero.
Time is effectively stopped for things traveling at the speed of causality (speed of light)
A “colder” object would have less kinetic energy and would actually have a more time-like worldline. It’s path though space time would be slightly closer to the geodesic and thus would actually have a faster clock relative to an object with a slightly less time-like worldline. But there are lots questions here on the reference frame too,
If we look at the full form of E=mc^2 we will see that (p) or the momentum is important.
E^2 = m^2 * c^4 + p^2 * c^2
So it is a question about what is experiencing the time, if you are talking about a box, or some random other collection of particles or the time for the sub particles. A colder temperature does reduce “E” very slightly but it doesn’t effect the world line if we talk about a bounded object to a meaningful amount.
If we look at the spacetime interval (s) displacement vector (r) and time (t) it is defined as:
s^2=Δr^2 - c^2Δt^2
As the “displacement” of an enclosed system does not change due to temperature, and that bounded system does not “move” in x y or z the cold (slower than light) object wil still be traveling at c^2 through space time. If you play with that formula it will also demonstrate time dilation with speed of light travel.
As for the original question, time is just our perception of one dimension in 4 dimensional space time. Localized fluctuations in time would be detectable by looking for differences the speed of causality which is exactly how we detected gravitational waves.
A local change in the geometry of space is a change in the speed of causality.
If the speed of causality was not constant at a universe scale we would not see it, but that possibility does not fit with current experimental models and most theories and would not be testable.
There is in fact work to study THAT effect… the slight variation in the lines…
The OP is probably asking if time itself could be changing, so that a clock behaves different even though nothing else changed, not even the gravity affecting it.
Lots of interesting input.
I’m pretty sure that relativistic time dilation will effect every possible clock, from a mechanical watch to nuclear half lives. That’s part of what I am asking…if time were slowing, not in relation to over there, but compared to over when how could we ever know?
Those galaxies we see (via HST) 12-13 billion LY distant are rushing away really fast…so time out there (and back then) is passing a lot slower than it is here and now. And the lizard beings there would say the same of our galaxy. That’s just relativity.
What I’m talking about is what if the “dark energy” acceleration of cosmic expansion is due to time “shrinking” as space expands?
The diagrams that show inflation just after the Big Bang, and the current expansion all show a time axis that is stable. My question is what if that axis is compressing as space expands?
I, of course, don’t know exactly what it means for time to shrink…when we get into that, we have to ponder what exactly time is.
Just that space and time are seem to be closely intertwined…so I’m wondering if space can be expanding, then why can’t time be contracting?
And that leaves me not exactly knowing what that would mean, and having no idea if it could be detected.
All the photons we collect that we know came into existence billions of years ago are strongly red shifted. We account for this by inferring velocity, which assumes time has been passing at a constant rate. Is it?
There are three known distinct arrows of time: The entropic arrow of time (the future is the direction in which entropy is higher, and the past is the direction in which it is lower), the cosmological arrow of time (the future is the direction in which the Universe is more diffuse), and the particle physics one (which involves extremely obscure and subtle processes that are almost never relevant). All other things that people think of as arrows of time are just special cases of those three, almost always of the entropic arrow. In particular, the psychological arrow of time (the past is the time we remember, and the future is the time we do not remember) is rooted in entropy. Thus, if for some reason entropy were to reverse, we would not “see eggshells unbreaking”; it’d be just as though the Universe just ended abruptly at the moment of the reversal.
Why are you assuming that time, in an expanding universe, is “forward,” and in a receding universe, would be “backwards”?
Because, as Chronos said, its one of the fundamental arrows of time. It may not actually work that way, but there’s nothing currently ruling it out. We don’t have a shrinking universe to compare to.
I’m not assuming that. I’m asking if that’s right.
The rate at which an ideal clock visibly runs depends on its red shift/blue shift, which is a physical effect as it is directly observed as spectral shift. Time dilation though is not the visible rate at which a clock runs, it is the factor by which the time between two events differ in two different frames of reference, it is only directly observable when both observers are coincident with both events (e.g. the twin paradox).
In special relativity, axiomatically, all inertial observers have global frames of reference, so in SR for inertial observers time dilation is global. However this is not the case in GR and time dilation only makes sense locally, though the concept of time dilation can be extended to gravitational time dilation for static asymptotically flat spacetimes.
In cosmic spacetime we visibly observe the clocks of faraway observers to be slowed down (i.e. red-shifted), however we do not attribute any of that to time dilation, we attribute it to the expansion of space. We could in principle, instead of attributing the red shift to expansion, attribute the red shift to clocks running slower in the past. The dilation factor would be dt’/dη when the presently observed light was emitted, where t’ is cosmic time and η is the comoving distance between the light and the object which emitted it multiplied by c (η is called the conformal time).
This ‘cosmic time dilation’ would not be what is normally understood as time dilation though as the present observer and past observers are not comparing the difference in perceived time between the same two events. So whilst this way of looking at things is not necessarily incorrect, it is not particularly useful either, whereas the expanding Universe paradigm is.
A relevant take by a webcomic:
http://www.rhjunior.com/the-probability-bomb-45/
Note: author is a Creationist and is using scientific evidence to disprove commonly accepted Evolution and Big-Bang Cosmology theories.
(sorry, only two pages available at this time)
But if we think the lizards are experiencing time more slowly, and the lizards think we’re experiencing time more slowly, which of us are correct?
The answer is that from our perspective they are zooming away at fantastic speed, while we stay still. From their perspective we are zooming away, and they stay still.
But we can’t compare clocks with each other unless we both end up in the same frame of reference. Take a spaceship and travel at 99.99999% light speed for 12 billion years until you get to the home of the lizard people, and compare your clock. Ooops, now we see that your clock is slower than theirs. But that’s because of the 12 billion year near-lightspeed trip you took to visit them.
Time dilation is always relative. To a guy on a spaceship blasting off from Earth at 99.99% the speed of light, he’s stationary and it’s the Earth blasting off. Or to put it a third way, the Earth is traveling through space at 99.99% the speed of light, and he’s just slowing himself down.
So which frame of reference is correct? If the Earth really is blasting off at .9999c, then the rest of the galaxy and the rest of the local galaxies and all the other nearby galaxies are doing the same. But, as you say, from 12 billion light years away it makes sense to say that the Earth is zooming away at some fantastic speed, and from even farther away it makes sense to say that the Earth is moving away faster than the speed of light, and so even if you could travel at lightspeed you’d never be able to reach Earth from that distance.