this post was submitted on 03 Mar 2026
16 points (94.4% liked)

Ask Science

15764 readers
30 users here now

Ask a science question, get a science answer.

Community Rules

Rule 1: Be respectful and inclusive.Treat others with respect, and maintain a positive atmosphere.

Rule 2: No harassment, hate speech, bigotry, or trolling.Avoid any form of harassment, hate speech, bigotry, or offensive behavior.

Rule 3: Engage in constructive discussions.Contribute to meaningful and constructive discussions that enhance scientific understanding.

Rule 4: No AI-generated answers.Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.

Rule 5: Follow guidelines and moderators' instructions.Adhere to community guidelines and comply with instructions given by moderators.

Rule 6: Use appropriate language and tone.Communicate using suitable language and maintain a professional and respectful tone.

Rule 7: Report violations.Report any violations of the community rules to the moderators for appropriate action.

Rule 8: Foster a continuous learning environment.Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.

Rule 9: Source required for answers.Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.

By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.

We retain the discretion to modify the rules as we deem necessary.

founded 2 years ago
MODERATORS
sabbah@lemmy.world
AradFort@lemmy.world
ken_cleanairsystems@lemmy.sdf.org
count_of_monte_carlo@lemmy.world
16
What would it look like if time were expanding? (pawb.social)
submitted 2 hours ago* (last edited 2 hours ago) by OwOarchist@pawb.social to c/askscience@lemmy.world
12 comments fedilink hide all child comments
 

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?

all 13 comments
sorted by: hot top controversial new old
[–] NaibofTabr@infosec.pub 3 points 47 minutes ago

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.

[–] birdwing@lemmy.blahaj.zone 1 points 46 minutes ago

Entropy quickening, perhaps? But the thing is, it's not time or space - it's spacetime.

[–] nirodhaavidya@lemmy.world 4 points 2 hours ago

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.

[–] UNY0N@lemmy.wtf 2 points 1 hour ago

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.

[–] Dave@lemmy.nz 3 points 1 hour ago* (last edited 1 hour ago)

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).

[–] bjoern_tantau@swg-empire.de 2 points 1 hour ago* (last edited 46 minutes ago) (2 children)

I mean, we do know that time slows down in a gravitational field ~~. And it speeds up for~~ and 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.

[–] fallaciousBasis@lemmy.world 3 points 1 hour ago (1 children)

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.

[–] bjoern_tantau@swg-empire.de 1 points 49 minutes ago

Thanks, something felt off when I wrote that.

[–] NaibofTabr@infosec.pub 0 points 1 hour ago

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

[–] cAUzapNEAGLb@lemmy.world 2 points 2 hours ago (1 children)

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

As for how we would perceive times expansion speeding or slowing, i dont think we can, but maybe we could infer it like counting tree rings, but ive no clue

I'll caution that my above is from my imagination not any citable journal article or experiment

[–] OwOarchist@pawb.social 2 points 1 hour ago* (last edited 1 hour ago)

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.)

[–] Ftumch@lemmy.today -1 points 1 hour ago

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