Okay, I know it sounds weird, but hear me out:
We know space is expanding, sure. That’s been established science for a while now. All three spatial dimensions at the same (increasing) rate.
So … why should we assume that the 4th dimension – time – is static and unchanging like we used to think space was? Could time also be expanding or contracting? (Expanding seems more likely, as it would match what the other dimensions are doing.) After all, spacetime is all one thing, really. Space and time are inextricably linked. When you think of it that way, it seems nearly impossible that space would be expanding while time is not. Spacetime is expanding, so wouldn’t that include time as well?
My question here is: what would it look like, subjectively, from our perspective inside it, if time was expanding just like space? Would we be able to measure it at all? Would there be any difference? Could the acceleration of space expansion (‘dark energy’) actually be explained by time expansion instead?
For a moment, imagine a universe where time definitely is expanding. Even if you don’t think time could really be expanding, let’s think about that hypothetical universe where it definitely is. What would that universe be like? How would it be different – if at all – from our universe?
Does it even matter? If time is expanding, but we still experience it passing at a constant rate, why would we even care whether it’s expanding or not? An observer somehow watching it happen from ‘outside of time’ might, say, see things happening slower and slower … but for beings living inside of spacetime, with their subjective perceptions also dependent upon the flow of time, would it actually change anything at all?
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It is not established that space is expanding. It’s a current model to help explain what we otherwise cannot explain.
We don’t have anything suggesting, for example, that this model is not in fact depicting a shrinking universe within a static spacetime, which would have the same physical measurable effects. It would simply be a matter of perspective. Shrinking objects would appear to be accelerating away from one another, and we wouldnt even need to answer the ‘expanding into what’ question.
So, just wanted to keep that ground you’re building this on unsteady. 🙃
Shrinking objects would appear to be accelerating away from one another
Um … not really.
Say, there are two stars 10 light years apart, and each of them has a diameter of .00000014 light years. If all that’s happening is that they’re shrinking, the distance between them will increase, yes. But even if each of them shrinks to a diameter of essentially zero, the distance between them has only increased to 10.00000014 light years.
If you were measuring the distance based on the star’s diameter as your unit of measure, then yes, as your units changed, they could appear to be much farther apart. But as long as your measurement scale remains consistent, ‘everything is shrinking within a static spacetime’ doesn’t really hold up. (Maybe it would work if the speed of light is also shrinking, slowing down over time?)
So … why should we assume that the 4th dimension – time – is static and unchanging like we used to think space was?
It’s not…
Einstein realized it and Hawking and Penrose proved it.
Time is relative, so not only is it not unchanging, it’s not consistent.
Even gps satellites experience time differentlynthan the same clock on the surface would.
If the universe is expanding or contracting, that means everyone’s “time” is either speeding up or slowing down to a hypothetical “center clock” that stays perfectly still in the center of the universe.
We just don’t notice it because time is relative, we always experience the change, it would take an outside observer who’s speed in the universe is constant to even notice if ours changed.
Does it even matter?
Nope
Not a scientist, but if time were expanding I’m not sure how you would notice that subjectively. I imagine it would be like black hole time dilation. You’d still experience things at 1 sec per sec, it’s just that your second is longer than an outside observer. But that’s a wild guess by a relative idiot. Hopefully soon to be corrected.
Edit: Oh, I’m just saying what others have said better.
My opinion, but I think you are right: Time is just ‘change’. No change, no time. ‘Expanding’ time, must mean that the time-interval is getting longer, so time slows down. If time slows down in our whole universe, all forces etc would slow down and we wouldn’t notice anything different (assuming forces are time-step dependent). Only an outside observer to the universe would notice it.
However, we notice relative time dilation like clocks on satellites etc…
If you assume that space is expanding, then time is also expanding.
The expansion of the universe cannot be observed locally, you have to look at something very far away to see the redshift of some distant star or galaxy. By doing so you are looking back through time. The farther away you look, the farther back in time you are seeing. But the rate at which the distant objects are accelerating away from you is not static, it is increasing as the distance increases.
So the time it takes for the light to get to you is increasing. Time is expanding relative to you. Time and space are not separate, they are linked. If something gets far enough away, then the time it takes for it’s light to reach you becomes infinite, essentially removing it from your existence entirely.
But the rate at which the distant objects are accelerating away from you is not static, it is increasing as the distance increases.
Then … could this be explained through time expansion, without any need for ‘dark energy’?
Maybe? The truth of the matter is that we don’t really know very much about reality. Dark matter and dark energy are placeholders for something in reality that we have no explanation for, like the nested heavenly spheres of the earth-centric astrophysical model that describe the retrograde motion of the planets.
https://en.wikipedia.org/wiki/Celestial_spheres
The expansion of the universe is also likely to be a misinterpretation of reality as it really is. Especially with findings of the james web telescope, we are constantly finding phenomena that show us just how little we understand.
And if you learn about evolution and perception, you start why we can get things so wrong.
The biggest problem with measuring any such effect is our frame of reference. All of our measurement tools are stuck in Sol’s gravity well, which is itself stuck in the Milky Way’s gravity well, and so on.
There’s a lot that we don’t know, because our viewpoint is limited. For example, the gaps in this chart of observed galaxies:
are caused by all of the objects in the Milky Way which are blocking our view of more distant objects.
We do know that there are a lot of other galaxies around ours, and that they move through space along measurable and predictable paths. Gravity affects time, so time doesn’t necessarily progress uniformly everywhere, but at least for the observable universe it must be fairly consistent otherwise we would see strange behavior in the frequencies of light from observed astronomical objects (it would mess with redshift/blueshift). Astronomy relies heavily on redshift/blueshift data, so anomalies would not go unnoticed.
otherwise we would see strange behavior in the frequencies of light from observed astronomical objects (it would mess with redshift/blueshift)
That’s kind of the thing, though. We do see strange behavior – a lot more redshift than expected, with more distant objects redshifted more than closer ones. And the rate is increasing.
Currently, we rely on ‘dark energy’ to explain the increase … but dark energy remains completely undiscovered and – other than its effect on expansion – undescribed. Could ‘expanding time’ explain it better, perhaps?
(You’d only want to explain the acceleration of the expansion through expanding time. As for why the spatial dimensions (or indeed time as well) are expanding in the first place… Well, that’s a deeper question I don’t think this line of thinking could address.)
It’s an interesting question, that from my searching around we don’t really know if time is expanding or what that would mean.
One interesting answer I found is this:
The simple answer is that no, time is not expanding or contracting.
The complicated answer is that when we’re describing the universe we start with the assumption that time isn’t expanding or contracting. That is, we choose our coordinate system to make the time dimension non-changing.
That is to say, we know time is not expanding because we use time as our scale. The link has a bunch of maths if that’s your thing.
I also found a suggestion that time expanding would likely act like other time dilation, that is to say that it would only be noticeable by an independent observer (such as if a spacecraft were traveling near the speed of light, those on board might only experience a few weeks passing as it travels to Alpha Centauri, but for those remaining on earth it may appear as 5 years).
I mean, we do know that time slows down in a gravitational field
. And it speeds up forand fast objects. We have to consider that with our GPS (and similar) satellites. They are basically just atomic clocks sending down their current time. They have already drifted from clocks on the ground by several seconds.In terms of time dilation influencing expansion you should look into timescapes. If I recall correctly it is meant to explain the apparently accelerating expansion by time moving faster in emptier regions of space.
This stuff is just hard to study on a cosmic scale because we don’t know exactly where everything is in the universe. Building a 3d map of all the galaxies is super hard and in parts relies on correct assumptions about expansion.
I mean, we do know that time slows down in a gravitational field. And it speeds up for fast objects. We have to consider that with our GPS (and similar) satellites. They are basically just atomic clocks sending down their current time. They have already drifted from clocks on the ground by several seconds.
GPS is my favorite demonstration of relativity in practice. Technically, the clocks have not drifted, but are in fact self-correcting and account for the effects of special and general relativity.
Special relativity predicts that as the velocity of an object increases (in a given frame), its time slows down (as measured in that frame). For instance, the frequency of the atomic clocks moving at GPS orbital speeds will tick more slowly than stationary clocks […] The result is an error of about -7.2 μs/day in the satellite.
According to general relativity, the presence of gravitating bodies (like Earth) curves spacetime, which makes comparing clocks not as straightforward as in special relativity. […] In case of the GPS, the receivers are closer to the center of Earth than the satellites, causing the clocks at the altitude of the satellite to be faster by a factor of 5×10−10, or about +45.8 μs/day. This gravitational frequency shift is measurable.
Combined, these sources of time dilation cause the clocks on the satellites to gain 38.6 microseconds per day relative to the clocks on the ground. This is a difference of 4.465 parts in 1010. Without correction, errors of roughly 11.4 km/day would accumulate in the position.
https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System
No. As an object speeds up, time dilates (slows.) Length contracts. Outside observers see this as slow mo. Internal observers see this as business as usual.
Thanks, something felt off when I wrote that.
Entropy quickening, perhaps? But the thing is, it’s not time or space - it’s spacetime.
In 4D space-time, assuming light travels a fixed distance for every perceived unit of time, I think that would slow the speed of light over time. Since light would have to travel further along the t axis, it could cover less distance along the X, Y and Z axis.
Disclaimer: I am not a scientist
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I beleive time is expanding as with space, the present is the boundry of the universe, the perimeter of but one dimension of its shape, the past is set within the body of the shape, but the future is yet to exist, it has not yet been expanded into
An interesting thought … and perhaps it could even explain the accelerating expansion of space? Not sure if I’m approaching the idea the same way as you are, but it’s giving me ideas.
Suppose time is a sphere, with the interior representing the past, the exterior representing the future, and the surface representing ‘now’. All three spatial dimensions are mapped to the surface of this time sphere. As the sphere expanded from past into future, the surface area of the sphere would increase. But not just increase at a steady rate! Let’s assume the ‘radius of time’ does increase at a steady rate from past to future. And then look at the relation of sphere radius (purple line) to sphere surface area (blue line):
(Not my work, just conveniently found in an image search.)When the radius is increased at a steady rate, the surface area increases at an accelerating rate. Objects on the surface of that sphere would be accelerating away from each other in all directions (just like we observe).
Viewing time as an expanding sphere and (contemporary) space as the surface of that sphere could potentially explain both the expansion of the universe and the ‘dark energy’ acceleration of that expansion.
(Though it does seem like something that would be very untestabable, unfalsifiable, and not particularly useful for making novel predictions.)
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