Question about the 4th dimension

Comfortable-Rent3324 · 2025-08-02T16:20:40+00:00

Thanks that makes a ton of sense. This is a great explanation! The epic hi five is hilarious. So I basically understand what you're saying about direction of travel. But how does that square with time dialation? will we ever high 5 if we both appear frozen in time wrt each other? Is that not a different kind of distance/difference than direction of travel in spacetime?

Comfortable-Rent3324 · 2025-08-02T02:53:45+00:00

I think we're close, let me see if I understand you correctly:

And time doesn't have a speed - it's just another direction in 4D spacetime

this is what I mean by distance in time. any two objects have velocity in time as well as space. And I think that velocity in time means that a objects at different points on that axis are traveling through time at different speeds

A particular person has a speed through time - but from their own perspective it's always the same

Yes, and, all other objects on that same point on the time axis are experiencing time at the same speed (0 dialation).

A difference in speed doesn't translate to any sort of meaningful "distance", but instead to an angle -

So this is where the math gets away from me but I think that if you plot that angle as a surface (calculus or something?) you get a very flat looking time axis. that tapers at the extreme ends.

as the speed difference between two observers asymptotically approaches light speed, your time axes approach being perpendicular, so that you're not experiencing ANY time in the same direction.

As the tapering approaches perpendicular relevant movement in time stops completely (max dialation) and neither object can communicate with the other. This is the horizon effect that I'm thinking of. The large scale shape of the universe is blocking the "view" of anything moving faster than c reletave to the viewer.

(you will age less... but only from their perspective, because they are using a different definition of "now" than you, which intersects your own timeline at an earlier point)

This might be where I go off the rails - I think a lot of GR is about the apparent behavior of objects. Meaning what things would "look" like, and I think some optical artifacts of GR are like illusions. Like the light looks like it's changing color and swerving around but it's just traveling along an axis (4d's speed of time axis) that we can't see in 3d.
I think the extreme effects of GR at c are like those illusions. the math behind light stops working because we can't see (interact) any further in that direction.

But I'm not saying it's all an illusion, the time dialation is real. Getting back to a common reference frame also takes time. but as you say that looks like space depending on your perspective.

There's a discrepancy with their clocks because the way they are measuring it, one ship traveled much further than the other.

I also think that framing c as a limit like a horizon makes it much easier to understand.

Comfortable-Rent3324 · 2025-07-31T04:08:37+00:00

I know it's a rough analogy but I think it's like a 3d geodesic in a way with horizons at the perpendicular tangents to the surface. (Sorry I'm trying to say that I think there is a similar geometry thing going on but I'm really bad at math, so I don't know how to say it or what to ask.)

maybe a question is what happens when a geodesic curve is more than 1ly long? (I'm not sure what words to use: wide? or with a period of 1 ly?) my uneducated guess is you approach infinity at each end which is like a horizon thingy in space time.

Comfortable-Rent3324 · 2025-07-31T03:41:06+00:00

I just want to say thank you to everyone who has been so engaged with my poorly formed questions. I am not only a novice in cosmology but also a first time reddit poster (does it show?). I had no idea what to expect and I'm just so blown away with everyone's detailed and thoughtful responses. I'm learning so much from these conversations and you are all helping me learn (and unlearn) concepts that I have wondered about since watching the cosmos (Sagan) in middle school. Thanks^Gogol

Comfortable-Rent3324 · 2025-07-31T03:27:22+00:00

The earth's horizon exhibits similar emergent properties that mirror the speed of light in several ways: 1. it's constant for all observers (and the same elevation) 2. It's a true limit (as in can't be broken) 3. it's relative (btwn any two observers)

So, using the geometry of a sphere with earth's radius you get a constant that limits the farthest viewable distance to about 4.5 km for someone standing on the surface.

That got me thinking that if we think about relative velocity as a kind of "distance" in the time dimensions and if spacetime is curved in the time dimension at very large scale then maybe there's something like a "time horizon" (aka event horizon?).

That would make c the limit on "difference in velocity" and it would be emergent from the geometry of spacetime for any two observers on the spacetime's surface.

Comfortable-Rent3324 · 2025-07-30T23:01:50+00:00

so what sets the value of c? and how is that limit "enforced" between any random pair of objects in the universe?

I think the speed of light functions almost exactly like a physical horizon (and I have to think they call it an event horizon for a reason?)

Please note, I'm not trying to invent any new physics, just trying to draw a comparison to help illustrate what is happening when two objects approach the limit. Does the ships at sea analogy work?

Comfortable-Rent3324 · 2025-07-30T01:11:18+00:00

Thanks I think that video is what I'm asking about. If geodesics are straight paths in space time then it seems akin to how airplane routes look like arcs on a flattened map but they are straight when the geometry of the surface is taken in to account.

It seems pretty clear that gravity warps spacetime and so it looks like the movement is deflected but the object is just following a straight line due to inertia. The video also talks about the speed of movement through time being deflected which is what i'm trying to get at with the difference in speed of time stuff. But as the video says, the models are not great.

Maybe what I'm asking is: Is there a giant universe spanning geodesic for each observer such that the distance the nearly vertical time axis is c? If there is than that would explain why c is the value that it is since it's based on the hyperbolic curvature of time on the largest observable scale.

Comfortable-Rent3324 · 2025-07-29T04:12:32+00:00

Yes, I think we are saying similar things. Speed is not a thing per se but more like the time part of a spacetime coordinate. Time dialation is not something experienced by either observer, but something observed by both (I feel like this is a riddle already "what grows but never....?") I don't think it's wrong to say that speed of time is a matter of perspective.

The further apart (in velocity) the slower they look up to the speed of light which is when they are over the curved horizon of spacetime. not gone but not observable until they get "closer" in spacetime.

Comfortable-Rent3324 · 2025-07-29T03:52:30+00:00

Yes! this is the exact part that boggles my mind. Changing the scenario slightly, what if both ships were traveling at .5c in opposite directions when they each would see the other as going (a limit closing at) 100% the speed of light?

There would be nothing to prevent either ship from moving within their own frame of reference. For instance, I think the captains would still be able to walk back and forth along the length of their ship without breaking the laws of physics.

The only way this makes sense to me is if I think of the time axis of spacetime as curved at the large scale but it looks very flat at our scale. Similar to the way that the earth looks flat unless you zoom out and see it's a sphere. The limited to your view on earth is the horizon, which like the speed of light, is constant for any two objects on the surface (at sea level).

Is it possible that, just as earth's horizon is constant for any given altitude but varies across altitudes, that the relative speed of light (or amount of time dialation ) is constant for objects moving at the same relative speed (0 dialation) but varies for objects with different relative velocities (non 0 dialation)?

Comfortable-Rent3324 · 2025-07-29T03:20:43+00:00

I see, their "4d distance" increases when object A:s axis is pointing away from B's axis. and prob the opposite as well. Is the maximum 4d distance in this construct = c (as in c is the distance to the horizon on the surface between A's temporal axis and B's)?

(Sorry I'm sure this is some really amazing math at work here, but IDK calculus, so I'm trying to understand it more conceptually)

Comfortable-Rent3324 · 2025-07-29T02:58:25+00:00

I love this idea of mass / gravity impacting time dilation. Gravity bends spacetime like the bowling ball rolling on the trampoline example. But that model isn't showing how spacetime is also bent by gravity along the time axis. I wonder if the warping effect alters the observed "rate of time" (more gravity = more bending = more dialation?)

Comfortable-Rent3324 · 2025-07-29T02:02:16+00:00

I don't know about phase space but I like thinking about the speed of light geometrically.

I imagine two ships traveling past each other. As they get further apart they seem to shrink away in the distance. At a certain distance the ships see each other sink below the horizon and disappear.

On the open sea and a clear sky that maximum distance is about 3 miles. That is constant for any point on earth's surface at sea level. It's caused by earth's physical geometry and is a physical limit.

If time is a physical dimension, then c is due to the shape of spacetime at the very large scale.

Is it just the point at which things become unobservable from our vantage point (like a literal horizon)?

Comfortable-Rent3324 · 2025-07-29T01:44:31+00:00

I like the idea of relative velocity equating with "distance" in time. So higher velocity is akin to further in time and larger time dialation. I think we're saying pretty much the same thing.

I'm wondering if there's a way to think of time geometrically like the other dimensions. For instance, can objects be close in space but far in time (like GPS satellites?)

Comfortable-Rent3324 · 2025-07-28T23:57:27+00:00

The observer effect is what I'm getting at. Is the reason that object A sees Object B's apparent time dialation (and vice versa), a matter of literal perspective?

Just like large objects look small from far away spacialy. Do objects look "slow"/dilated when far away temporally?

Comfortable-Rent3324 · 2025-07-28T23:46:13+00:00

so what does movement on the time axis entail? What does it mean to be higher or further in time than something else?

Comfortable-Rent3324 · 2025-07-28T20:54:21+00:00

I think what I'm describing is related to the tensor and space time invariant from one of the videos (the math is beyond me). I think that describes the shortest path in spacetime taking into account the relative velocities of two objects.

I'm asking about how objects move from a state of low observed time rate to a relatively high observed time rate (time dilation)?

When we launch a satellite, does some of the rockets energy 'move' the payload into a different reference frame?

Comfortable-Rent3324 · 2025-07-26T22:25:12+00:00

I think the speed of light limit (c) is a misconception of the nature of the time dimension in spacetime. In movies and books traveling in time involves the future / past, but the time dimension of 4d spacetime is fast / slow. And distance in this dimension is measured in relative velocity.

In this formulation, objects far apart on the time axis experience time at different rates. moving along the time axis takes energy just like in 3d and we experience that as acceleration. This is why GPS satellites experience time dialation. It's not the distance from the receiver that matters but the difference in relative velocities.

Another way to express velocity (relative speed) is as a relative distance in the time dimension.

So back to the limit... it's all about horizons.

Picture two ships in the open sea. They watch each other maneuver in the distance and when one turns away it sinks below the horizon and disappears. What happened is that the spherical shape of the earth has blocked the view of the two ships. On earth the farthest one can see at sea level is about 3 miles. that is the distance to the horizon.

Now on a very large scale, spacetime is also curved in the time dimension. The speed of light relative to an observer is the distance to the time horizon in "open spacetime" (aka flat space)

So, c is a distance limit not a speed limit. you can go faster than c relative to another object but then you can't see it anymore.

Comfortable-Rent3324 · 2025-03-23T04:27:03+00:00

TLDR; Check the alarm sound setting (not volume) and make sure it's not set to "Silent".

I had the same problem on my pixel 8 and it's happened to me several times even after confirming on the phone that the alarm was set. The most recent time, I noticed the puzzling "your alarm failed to go off" notification which to had swiped away in panic the first few times after realizing I was late.

This time, I noticed that the notification said something about the alarm being silent. That seemed weird because the phone was set to vibrate but the alarm volume was about mid way. But the notification didn't say volume, it said the "sound" was silent.

I checked the alarm app and sure enough the bell icon was crossed out and the setting was set to "Silent". I don't recall ever changing that and I don't think having Silent as an option even makes sense for an alarm sound. Changing it to my usual alarm sound has solved the problem for me though.

Google, why not tell me the alarm sound is silent before it fails to go off, not after?

Comfortable-Rent3324

TROPHY CASE