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EGP22 t1_j1iv024 wrote

Reply to comment by bacondota in Are people in the international space station experiencing time faster than us? by [deleted]

I’ve always struggled to get this concept and I find your explanation very good. I think what still gets me is that if a second is a second, I still don’t get why someone moving at .5c appears to have lived “300 years” when the same amount of actual time has elapsed, “80 years.” I am dense though so this isn’t a lack of teaching rather learning.

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bacondota t1_j1j97wn wrote

300 years passed on Earth, on the spaceship only 80 years have passed. It gets funky so you just need to read from bunch of sources till it click.

For example, everything moves at C on the spacetime continuum. Since we are moving very slowly through space, it means most of our speed happens on the time part of the spacetime. Since light moves at speed of C, from the POV of the photon, it has no travel time, it just teleports from where it is emitted to where it hits something.

In other world, if we surpass all limits and build a ship that moves at 1C. Whoever is piloting it would never know when to brake because there would be no time flowing.

Edit: break > brake

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mayonnace t1_j1j5l4r wrote

What gets me confusing is people talking about light speed.

How I understand this is, time flows slower or is more stretched at where there is more energy/matter/particles stuff, and the difference of speed or stretchedness of time between two places results as gravitational force towards the slower or more stretched time-space which has more energy/particle/matter stuff.

In short, I guess, when we are having only one generation of people living and dying on earth, on a planet with much less gravity, there might live perhaps three or four generations of people (this may or may not be possible due to people not being able to survive or reproduce in very low gravity, but let's ignore it since I don't know how to calculate that).

I still don't know what the light of speed has to do with that, since speed is related to distance, and what time is related to are energy density or gravity. I'd appreciate if someone could somehow grant me access to that part of this wisdom, that is teaching it to me somehow. Just pick my example of two planets if possible.

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bacondota t1_j1jh59e wrote

Speed of light is the speed of causality. And you are trying to separate Time from Space. It is not 'time' that is related to gravity, it is the 'SpaceTime fabric'. It is one thing

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mayonnace t1_j1jo8ei wrote

Does stretchedness of space also change depending on matter/energy/particles stuff, like time does? If so, then in which direction? If we have more particles accumulated in a point space-time, time seems to be streching up, how about space? Does it shrink? Bend? Enlarge? Do distances change? Or is it just that it takes more particles per volume unit, like its volume getting stretched up?

I guess I'm still thinking them separately, but if I can get the space perspective as I did with the time, perhaps I could try to blend them together easier.

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t3hmau5 t1_j1ju2ts wrote

Gravity is the result of matter warping spacetime.

Imagine setting a really heavy bowling ball on a trampoline. It will sink, stretching and curving the fabric of the trampoline that otherwise was flat, uncurved. If you were to roll a smaller ball straight past (but not at) the well created by the bowling ball, it will circle the well, gradually spiraling inwards as it loses energy. Analagous to one body orbiting another.

Matter does pretty much the same thing to spacetime, but its in all directions (since spacetime isn't a flat plane like the trampline). Non-euclidean geometry is the geometry of curved surfaces (put simply) and can shed insight on some of your more specific questions.

Edit: watch this Video

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mayonnace t1_j1k32u1 wrote

That's a fun video. Thanks!

I've seen the fabric metaphor before, but I'm still having difficulty on not separating time and space from each other. I think now I'm very close to understanding though.

I'm starting to think that space is not really a volume, and it's more of a relative thing. Like if right now we could get rid of the half of the matter in space, like draw a line and cut it into two pieces like a pie, and simple erase one side, then the new center of the space would be the center of mass of the remaining half. Or let's say, if there was only one particle in the whole universe, then there would be no space since it couldn't move relative to anything. It couldn't have speed. So, space is not actually an empty volume, if there aren't more particles that can move relative to each other. What do you think? It's not correct, right? Is it?

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dazb84 t1_j1jtoqi wrote

The problem is our daily experience of how time and space operate is actually misleading. This makes it really unintuitive to conceptualise what's actually going on.

It turns out that time and space are the same thing which is called spacetime. Everything moves through this spacetime at the speed of light. There actually isn't any variation in speed of anything through spacetime. The only difference between anything is how much of their lightspeed through spacetime is specifically directed at moving through space and how much is directed at moving through time.

In order to move faster through space, you must deduct speed away from time because you have to maintain lightspeed through spacetime. This is also why you can't go faster than light. Firstly, you're already travelling at light speed through spacetime. Secondly, once you angle all of your light speed through spacetime so it's pointed at space then you have 0 angled at time and so you have no more speed to borrow from time to assign towards speed through space since you must always maintain lightspeed through spacetime.

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komor555 t1_j1je8zi wrote

If you'd travel at the speed of light, time would stop for you relative to the universe completely. Accelerating faster you'd be going back in time, in theory. I don't know the relationship between time and light, but I suspect that light has to follow the same rules as everything else that has a mass and travels.

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mayonnace t1_j1jmdjt wrote

That's weird. If I was a photon, trying to travel from a lamp on Earth to some very far away planet, you say, time would stop for me. But if time stops, there can't be motion, and I would never leave from that lamp on Earth in the first place. I would just glimpse into existence, and stop forever, or something like that.

Or I guess you mean like, everything stops, but me. In that case, my birth into existence and arrival on my final destination would be instantaneous. I'd get born, travel, and die at the same time.

Ooooor, that would be how everything else would see me as, happening instantaneous, while I'm actually having lots of fun during my travel, seeing how nothing is moving, perhaps except other photons. Is that it? But this couldn't be true either, because we don't see light's movement instantaneous, we see it with a delay depending on its distance, like we keep seeing old stars that aren't there anymore...

It doesn't make sense. Sorry. Perhaps I shouldn't have put myself in place of a photon. I don't know.

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I__Know__Stuff t1_j1jo0or wrote

> my birth into existence and arrival on my final destination would be instantaneous. I'd get born, travel, and die at the same time.

This is correct. To an outside observer (us), it takes a photon about 8 minutes to travel from the sun to the earth. To the photon itself, it is instantaneous.

One of the ways that it was determined that certain neutrinos have mass is that there is a nonzero probability of them mutating while they travel between the sun and the earth. If they had zero mass, they would travel at the speed of light, and there would be no passage of time during which they could mutate.

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mayonnace t1_j1jr7ki wrote

I see, but that's weird.

In this sense, if this time-speed relation is continuous, the faster a thing will move, the less time flow it will experience. And as someone else suggested, if one could accelerate further, then it would have to see things going back, but that confuses me and it's another story, because me accelerating further would require me being observed as going backward too, but I'd be going the same direction... Then perhaps it's an automatic thing that, after this speed limit, the direction of the vector just rotates itself backwards? But that doesn't sound nice either.

I guess we will have to assume, speed of photon is the maximum, and zero is the minimum, and there can happen no bending beyond these extremes due to some dimensional restrictions or something.

Then, in a similar sense, something with zero speed, should experience the whole time being as fast as a moment, like the cosmos gets born and dies at the same time, yet it might have to stay still at the center of the universe for that, because its coordinates should never change to never have any speed, and at the beginning it was a point, I guess.

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feral_engineer t1_j1kddjk wrote

When time stops it stops in a reference frame. There is no motion in that reference frame but the frame can still move through spacetime relative to other reference frames. Think of light as a permanently frozen object. It pops into existence and does not change. It can still move through spacetime. The concept of instantaneousness does not apply to frozen objects. They don't experience time ever.

Similar to motion, a reference frame where time stopped can spin. That's how the singularity in a black hole behaves. Time is stopped in it but it still spins. When matter falls into the black hole angular moment adds up so it can spin up or spin down while still experiencing no time (remaining frozen).

Note that light frequency is not a movement in addition to the movement of light along geodesic lines. A frozen object can have internal frequency, spin, and momentum.

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whatissevenbysix t1_j1jp06b wrote

You actually got it. From a photon's perspective time doesn't exist. It instantly comes into existence and dies at the same exact moment.

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[deleted] OP t1_j1j66xu wrote

[deleted]

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mayonnace t1_j1j8690 wrote

But Wikipedia says, it's 299,792,458 meters per second in vacuum. And we get to see things happening far away way later due to this delaying factor. Like, a star explodes, but we keep seeing it, because its light from past is still on its way.

Also, I still don't get how this is related to time for two colonies living on two different planets. I have a bad feeling that you're trying to mess with me, pal.

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throwawayzufalligenu t1_j1j969b wrote

Spacetime is hyperbolic. Considering time dilation, that speed is instantaneous if you were riding that photon sans mass*.

Here's a comment from a few years ago and its parent with a better worded answer: https://www.reddit.com/r/askscience/comments/n3qgk/if_light_travels_from_one_point_to_another/c361txy/. If you were riding the photon you'd think you teleported but someone on earth you have measured you going at the speed of light.

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whatissevenbysix t1_j1jopyn wrote

The whole point of relativity is that there is no such thing as "actual time". That's the big revolutionary idea. It says that time is, much like speed, relative. So, from the perspective of the fast traveler, their perspective of time elapsed is 80 earth years. But from the perception of the person on earth, it's 300 years. Neither is "actual time", they're both correct.

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Malkiot t1_j1jpaui wrote

Imagine a normal graph with an X and Y axis. X is rate of movement through space and Y is rate of movement through time. The Vector (length of the arrow) of your movement through X-Y (space-time) has a constant length. So if you move at a greater rate through space, you must move at a lower rate through time to keep the arrow at the same length (Pythagoras).

At the speed of light the arrow is perfectly horizontal, with no movement through time and at a velocity of 0 you are maximally moving through time.

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dazb84 t1_j1jskn6 wrote

In any given locality there are fundamental laws like not being able to travel faster than lightspeed and this also applies to the passing of time. It will always pass at one second per second for any local observer. Another law is that events between these different localities ultimately must be causally linked. The only way for events from one to impact the other and retain that causal relationship is if you introduce the concept of time dilation.

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ghostowl657 t1_j1j7bzk wrote

Your misunderstanding comes from your thinking there is such a thing that "actual time has elapsed". Not everyone's second ticks at the same rate, and there's no way to say that mine is more valid than yours. But to the person actually on the ship they still feel like time moves "normal" since every physical process is dependent on the local flow of time.

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EGP22 t1_j1j8if2 wrote

Is not a second a unit of measurement and constant, thus one second is equivalent anywhere? This is the concept that I don’t understand.

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dazb84 t1_j1jw1nm wrote

It is, in the same way that light speed is the same for all observers. For example you travelling at the speed of light and turning on a flashlight results in the light emitted from the flash light moving forwards at lightspeed relative to you and we know that you can't go 2x the speed of light which is what would be happening from a 3rd perspective.

So the only way to reconcile this impossibility and maintain causality throughout the system, since nothing can go faster than light relative to any observer, is with time dilation.

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ghostowl657 t1_j1j8pvs wrote

It is a consistent unit of measure, but what everyone measures as a second is relative. The same thing is true for lengths.

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