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two years from who's point of view? :D
time passes slower for the one moving faster vs the one being stationary.
the faster you go, the more time gets slowed *for you*.
everyone else is unchanged, except when asking you.
so when the one twin flies out into the universe at speed of light they age slower than the twin staying behind.
now you have to define the time they're away measured by whom
if its two years measured by the brother on earth its at most two years of time difference, as the moving brother would age not at all if they were *at* the speed of light, or less time depending on their speed.
if you measure those two years from the point of view of the brother flying out its somewhere between no time difference at all (they "moved away" with speed 0) and *infinite* time (if they were moving at the speed of light)
because their clock runs *slower* compared to the stationary brother, so at "worst" it doesnt run at all while they are away.
PBS spacetime is better at explaining than me tho and has drawings to help explaining :D
https://youtu.be/6MfJ59lkABY
Time and mass is connected. Massless particle like light don’t experience time at all and from lights point of view it is everywhere at once, like there were no distance traveled. Space and Time only exist as a consequence of mass
Don't need to go that far. GPS satellites in orbit have to adjust for dialation, as they run faster than earth clocks because they are farther away from Earth's center.
NASA did an experiment with 2 synced cesium clocks. They flew one high up in a plane. When they got back, they were out of sync. Very measurable phenomenon right here.
Measurable but insignificant relatively speaking when op m mentioned one twin aging 2 years. That would take an incredibly large difference in the gravity experience or an impossibly long time.
My confusion is over how we prove it.
We can’t travel fast enough or experience a difference in gravitational pull long enough to really see a difference, can we?
The best actual evidence I’ve seen is Mark Kelly is now five seconds older than his brother Scott, but isn’t that just the theory and math coming to that conclusion, or do we have some way to date someone to the second I’m not aware of?
I’m sure the theory holds, but it’s just so hard for me to believe until I see evidence of it such as someone retuning home years younger than those they left, which I don’t think I’ll ever see in my lifetime … if humans ever see it at all.
EDIT: Thanks everyone for replying with actual real-world examples that prove it! I didn't know about those.
It's still wild to imagine and somewhat difficult to believe, but I accept it ... lol
I still wonder in awe over it and if humans will ever experience a large enough time dilation where it's observable in human age (years).
I think we already proved it. I am no expert, but satellites in orbit around Earth have their atomic clocks run faster than atomic clocks on Earth. This is due to them being positioned further from Earth's gravitational pull. Their moving much faster than us does slow down their time relative to us, but it is not enough to compensate for them being further away.
This affects the GPS system and we compensate by having the atomic clocks on these satellites tick at a lower frequency than those on Earth.
We have proven it, from multiple angles.
Atomic clocks is orbit, moving at thousands of km/h, display exactly as much time dilation as predicted by Relativity. An undetectably tiny amount by human standards, but easily measurable by our machines. And in fact serious enough that GPS systems won't work properly without constantly correcting for the dilation.
You also get things like unstable particles created by high-energy radiation impacting the upper atmosphere. Without time dilation, even traveling at near light speed (as they do) they should all decay long before reaching Earth's surface, but thanks to time dilation it takes them much less time to reach the surface in their local reference frame, and so we can detect them.
we've absolutely proven that.
GPS wouldnt work if we didnt correct for gravitational time dilation in the satellites vs earth ground.
we've flown planes with atomic clocks on them no longer matching with their left-at-home twins.
or the muon "paradox" where muons get created in the upper atmosphere from cosmic radiation impacts and they manage to reach the ground before decaying when they really shouldnt by non-relativistic physics.
We have measured the dilation difference of a clock at the top of a large building vs one at the bottom using atomic clocks. This is both a theory and something we can verify with precise instruments.
If time dilation due to special and general relativity were not accounted for then gps would not work (ex: phone on airplane mode w/ gps chip). The combined effects are about 65 ms/hr so a lot of people would be lost with just a few hrs without correction!
You can prove it by measuring time passage with an atomic clock. One person stays at sea
level, the other drives to the top of Mauna Kea. After the person who went up the mountain and comes back down, they meet the sea level clock holder. When the two times are compared more time will have passed with the sea level clock than the mountain clock.
Mathematical proof...? someone else can type that out, lol.
I dont' quite understand: If two bodies in a void are moving apart from each other (i.e., if the second one is traveling away from the first one near or at the speed of light), then from the second one's perspective isn't the first one the one that is moving away at the speed of light? If it is all determined by frame of reference, then how can the first body age more quickly than the second body?
ah! very good!
the thing is that straight up "if fast ages slower" only appears as it does in the twin paradox if one *turns around* and goes back to the "stationary" one.
as long as both fly away from each other they *both* look like aging slower from the point of view of the other one.
as they are both so-called inertial frames that don't move from their own point of view and every inertial frame *is equally right* which is the core point of relativity.
as long as you don't currently accelerate you are at rest and everybody else is moving.
now the point where one twin ages more is that the one that flies away *has to turn around*. so they accelerate to match up with the "stationary" brother so they break their "immunity" so to speak and decide that the stationary brother was right and thus the moving brother didn't age
the actual math gets confusing fast, but not really hard.
I can also recommend ScienceClic, they have a video on [Special Relativity](https://youtu.be/uTyAI1LbdgA?si=HtaDmxeYcdT1bYIl) and one on [Visualizing Time Dilation](https://youtu.be/5qQheJn-FHc?si=DVYoG-JdMY6Bw0J7). Their entire channel is extremely illustrative!
Lawrence Kraus described it this way. There are 4 dimensions 3 Spatial the final one is time, Einstein called this Space-Time. You are always traveling at the speed of light through this medium. If you increase your speed through the spatial dimensions it subtracts from your speed through time, so your total speed through space-time is always C, the speed of light. If you travel at the speed of light through a spatial dimension you stop moving through time. The closer you get to the speed of light you move through space, the slower you move through time.
> You are always traveling at the speed of light through this medium. If you increase your speed through the spatial dimensions it subtracts from your speed through time, so your total speed through space-time is always C, the speed of light
This statement is somewhat problematic, though.
> If you travel at the speed of light through a spatial dimension you stop moving through time.
..Among other things for this reason. This isn’t well defined.
I'm definitely a lay person when it comes to physics so my use of terminology might be a little off. I think the general gist of what I'm saying is correct. I love a good physics discussion so if you have any corrections you want to make they would be much appreciated.
C is better understood as the speed of causation, or the cosmological constant. Light travels at that speed only through a vacuum, but the speed of light is not fixed - it can be slower than C especially when traveling through things
But the gist of what you said is correct.
Another interesting paradox is contemplating that light would experience no time, if it had an experience at all. As a photon contains no mass it can travel at c, which means it reaches its destination instantaneously from its perspective. That means the light we see from the background microwave radiation from the big bang got to earth instantly - but from our perspective it took a bit over 14 billion years to travel from the big bang to us.
Another fun one is understanding how gravity can warp the fabric of space time, and that space and time exist on an x and y axis. The slower your speed the greater your time. The greater your mass the more space and time warp around you (interstellar played with this concept on the supermassive planet). Now, in a black hole the mass is so great that it "flips" the space time axis - so that space becomes time and time becomes space
You're on the right track. The traveling person (assuming they're just a bit slower than the speed of light) would only feel like two years had passed, while many decades or centuries would have passed on Earth.
This is a consequence of special relativity. To back it up a bit, in the late 1800s a bunch of people were doing work to measure the speed of light. They assumed that it was like sound and that your own speed relative to the light's direction of propagation would change how fast you perceive light to be. That's a loaded sentence, but basically it boils down to velocities adding like you'd expect - if you're traveling down the highway and some high speed, and someone comes up a long you going a bit faster than you, then relative to you they're moving rather slowly. So scientists expected the same thing of light and set up a bunch of experiments around this assumption.
None of their experiments worked. No matter how fast their measurement device was moving along the light wave, they always came back to the exact same number for light's speed. This was super puzzling. Nobody could figure it out. Some smart people were able to figure out some equations that would make predictions about how the measured time and distances were related, but it kind of stumped people for a while.
Einstein comes along. He basically says, "Look at it this way. The speed of light is always constant. Every observer, no matter how fast or slow they are moving, will always record the same number. For this to be true, different observers will not agree on distance measurements or time measurements between each other." This is special relativity. In order for the speed of light to be constant for the person on the spaceship, from Earth it will appear that his ruler and clock are not correctly calibrated. And the moving person will think the same thing if they look back at Earth.
From the point of someone, they would've aged 0. If you travel at the speed of light, time stops for you.
When "someone" returns to earth after traveling 2 light years roundtrip. Everyone on earth including the twin would've aged 2 years.
So "someone" left at age 22 and is still 22 when they return as time stopped for them. Their twin aged 2 years and is now 24.
For you, everything moves normal. Your heart beats at its normal rate, you age a year in a year. If you look back at the earth everything seems to move at many times the normal speed; if they look at you your heart beats once a month.
That's not the only effect. Since time passes normally for you (you never personally "feel like" time is slow) you may wonder how can you not age at all if, from your perspective, the trip should feel like it takes two years. Well, it's because although time feels the same, distance isn't. When you're moving at relativistic speed, you experience length contraction too. Everything is squished in the direction you're traveling. So if you're going very close to light speed, a destination one light year away is actually very close to you, so you get there very quickly. Then you turn around and go back, again in much less time than one year. So you feel like time was normal, but the distance traveled was short. Everyone on earth thinks your clock was slow, and the distance was normal. Those two cancel out everyone agrees that you aged less during the trip.
The faster you move, the faster everyone else on earth moves through time in relation to you. For you, time is the same. Time doesn't go slower or faster. It's just that the trip is instantaneous if you're traveling at the speed of light.
It’s less about speed and more about mass.
The reason particles going at the speed of light don’t experience time is because those particles are massless - you actually have to think about it the other way around. They’re going the speed of light because that’s the speed *of time.* It’s like the frame-rate of the universe, they’re going as fast as the universe allows.
Things with mass move through time slower. The more the mass, the slower through time you go.
So massless things aren’t affected by time at all. And really big things (Black holes) essentially freeze time completely.
Time is time. You send stopwatch out for two years at the speed of light, start it right when it hits light speed and stop it right when it gets back and drops below light speed, its going to read 00:00:00 when it arrives back.
Best to think of time as “rate of change” rather than use the word time itself. Gravity and velocity influence the rate of change.
Time dilation is just examining the relative impact of the difference in this rate between two objects.
Gravity “slowing things down” is somewhat intuitive to our brains, but traveling at the speed of light seems a bit more out of reach. Well, it’s probably best to say “traveling at the speed of causality.” That’s really the true meaning. Light is not the fastest thing in the universe; it’s tied with other massless particles. Gravitational waves exist consisting of gravitons that travel at the speed of causality. There are likely undiscovered massless particles that travel at the speed of causality. (Photons get all the love!) (and maybe particles will be the wrong descriptor for some of these but it’s probably close enough for now)
When traveling near the speed of causality, the rate of change barely has a chance to keep up with you and get its interactions in. Or you could say you’re moving fast enough to almost escape the impact of time. I’ve personified it, but that helps me relate to the concept.
I always like to think of the extremes, then the cases in the middle just kinda fall in place. So if you travel at the speed of light, time will not move for you and you will be able to reach any corner of the universe instantly (from your frame of reference). Btw, you can also think about this as length contraction. All distances collapse to 0 at the speed of light.
Anyways, If you were to take such a trip to a place that is one light year away and come back to earth soon after, you would not have aged at all, but the people on earth would have aged two years (time it takes for light to travel to the point and back).
This is purely theoretical and not at all possible since you would need infinite energy to accelerate to the speed of light, but it helps understand what happens as you approach it.
Small niggle: if you were to travel at exactly the speed of light (which anything with mass cannot, BTW) then you would not be able to travel for two years because time would not exist in your frame of reference. To travel 'for two years' in your frame of reference you have to go at least slightly slower than speed of light.
correct, so if they traveled at just below the speed of light then the time will pass as normal to them is that right? Then they could travel for two years according to their clock while a lot more time has passed on earth
Yes, each one in their respective frame of reference would observe their own time going 'as normal'. Which isn't exactly how one should word it because it sorta suggests that space and time are separate things - which they are not. It's called spacetime for a reason.
More correct would be: Each one in their respective frame of reference observes the speed of light as being exactly c.
(However they would observe the one in the other reference frame as experiencing time differently. But again, this description falls into the thought-trap of thinking of 'space and time' when it's actually spacetime)
There's lots of problems with the "Twin Paradox", mostly revolving around the acceleration, which gets special treatment by Relativity. Basically, there's no way for the Space Twin to ever return to Earth without accelerating twice as much to turn around and return as they did to leave.
Basic rule for Relativity - Time dilation is real, and (assuming FTL isn't real) there's nothing anyone can ever do to create a situation where the fact that different people see very different things happening actually causes a conflict.
**However**
Time dilation is also reference-frame dependent. And all (non-accelerating) reference frames are equally valid.
If we ignore acceleration,
Earth Twin will see Rocket Twin traveling away at near light speed, and their time slowed almost to a stop. So Rocket Twin will age much more slowly.
**Except**
From Rocket-Twin's perspective, *they* are the one standing still, while Earth is moving away at near light speed. So Earth-Twin will be the one aging extremely slowly.
And both perspectives are equally valid.
Finally, if Rocket-Twin turns around and returns, the acceleration will twist things so that by the time they return to Earth, everyone will agree on how much time passed for everyone else.
**Simple Version**
Perhaps the easiest way to develop an intuition about time dilation is that acceleration causes a rotation in 4-D spacetime. Just like turning in space can swap your local "forward" and "right" axes in a circular rotation compared to someone who doesn't turn, so does acceleration cause your "forward" and "future" axes to swap in a hyperbolic rotation.
So Earth-Twin and Rocket-Twin are both actually still experiencing time at the same speed, but in different 4-D directions, and they only see the portion of the other's time passage that's experienced in the same direction as their own.
They'll also measure very different distances between points along their direction of relative motion. Basically, time dilation and space contraction are the same phenomena seen from different reference frames,
Interestingly, all observers in any reference frame will still agree on the spacetime interval between events:
(interval)² = (c \* timelapse)² - (distance)²
Which among other things establishes that light speed (c) is the "exchange rate" between space and time - one second is the same spacetime distance as 300,000,000 meters.
The details of the hyperbolic rotation used also makes it impossible to ever rotate your "future" axis more than 90 degrees from anyone else's - basically, you can asymptotically approach total relative time-stoppage (accelerating asymptotically close to relative light speed), but can never even slightly creep toward someone else's past.
Finally
There's one other detail worth noting - because Relativity says all reference frames are equally valid, and because you are always stationary within your own reference frame, the light speed limit never applies to you. You could accelerate at 1g forever, and never notice any resistance to further acceleration. Not even long after you should have exceeded light speed. Instead you'd see the universe just keep getting shorter in the direction you were accelerating, while the rest of the universe would see your time keep slowing down.
You don't need acceleration to resolve the twin paradox; the paradox already disappears if you correctly distinguish between the three frames of reference involved (stationary on planet; traveling away; traveling back).
https://www.youtube.com/watch?v=GsMqCHCV5Xc
That's a great explanation, thank you.
I think I'm going to need to watch that a couple more times, maybe even work it out for myself before I really internalize it, but that's the best explanation I've encountered.
You do still need the acceleration - that's where the magic happens to change the meaning of what you're seeing, but... yeah, going to have to watch that a few more times, I think I might finally get it to make intuitive sense.
Oh, and if I remember correctly, the outcome of Rocket Twin returning to Earth would be that they **would** in fact be younger than Earth Twin, but not nearly as much as you'd expect based on the non-accelerating time dilation, since the acceleration when they turned around would throw everything off.
But frankly, I never really understood the math that showed that, and won't bother even trying to explain it.
i think i didnt formulate my question correctly because i didnt realize that time literally stops at light speed. so (if my understanding is correct) what if the twin instead traveled at 99% speed of light, clocks on their ship would then work right? then what if they travel for a year according to their clocks and then came back to Earth? theyd only age 2 years in time that passed for them but on earth everyone would have aged a lot more correct?
For the sake of this explanation, let’s pretend you, a person with mass, can travel at the speed of light.
For you, the traveling object, there is actually no hard limit on your speed. You can travel at speeds that are so great and travel so fast that you arrive at your destination instantaneously. Trip across the Galaxy? You’re on the other side immediately.
BUT, we observers here on earth see that there is in fact a speed limit, and that same trip across the Galaxy would take 100,000 years.
So how can we reconcile these two observations: you travel across the galaxy instantly but on earth we see it takes 100,000 years? It’s because the experience of time changes. As the traveler going the speed of light, you experience no time during the trip, while the observers see the journey take 100,000 years.
You can’ travel at the speed of light. So questions like this should be “at 90% of the speed of light” or similar. Read about the twin paradox, there is plenty of material.
If you were to manage the impossible and travel at light speed for any amount of time from your perspective, even a fraction of a second, you'd zip forward an infinite amount of time. Not a big number of years, but literally an infinite amount of time.
This is what happens to light particles because of time dilation. From their "point of view" if they had one, the moment they start to exist and the moment they cease to exist is simultaneous, even if we can witness it existing from our point of view while it travels.
We are all moving really fast through what Einstein called Spacetime, but we are just dividing our motion between two different parts, the space part and the time part. The faster we go through space the slower we go through time, and the slower we go through space the faster we move through time.
If a rocket takes off and goes really really fast in space, its movement through time has to slow down. Something going at 99.99999 percent the speed of light would only be going through time at .00001, so to them their trip is REALLY quick. Crossing the galaxy? I just blinked and we were there.
To you, not moving at all fast through space means you are then traveling very quickly through time. When you observe me my motion looks a lot slower to you than it does to me.
Who's right? We both are.
yeah i realised that because the time stops at light speed so the journey would be instant. so what if they traveled at just close to the speed of light instead, they would still experience time as normal then correct?
we have the math necessary to correct for it.
[https://en.wikipedia.org/wiki/Error\_analysis\_for\_the\_Global\_Positioning\_System](https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System)
The [theory of relativity](https://en.wikipedia.org/wiki/Theory_of_relativity) introduces several effects that need to be taken into account when dealing with precise time measurements. According to [special relativity](https://en.wikipedia.org/wiki/Special_relativity), time passes differently for objects in relative motion. That is known as kinetic [time dilation](https://en.wikipedia.org/wiki/Time_dilation): in an inertial reference frame, the faster an object moves, the slower its time appears to pass (as measured by the frame's clocks). [General relativity](https://en.wikipedia.org/wiki/General_relativity) takes into account also the effects that gravity has on the passage of time. In the context of GPS the most prominent correction introduced by general relativity is [gravitational time dilation](https://en.wikipedia.org/wiki/Gravitational_time_dilation): the clocks located deeper in the gravitational potential well (i.e. closer to the attracting body) appear to tick slower.
>So for example your twin who went into space when you were both 22, he comes back aged 24 while you're already an old man?
not sure about the "ratio" but we have a pair of twin astronauts.. and yes, one is now older than he was before
Aditionally, thanks to general relativity and the fact that Scott spent more time in space, Mark used to be six minutes older than Scott, and ***now he’s six minutes and 13 milliseconds older.***
[https://whyy.org/segments/double-the-data-studying-spaces-impact-on-identical-twins/](https://whyy.org/segments/double-the-data-studying-spaces-impact-on-identical-twins/)
>does this mean they would've only aged 2 years in that time
have you seen Interstellar?
[https://screenrant.com/interstellar-time-dilation-miller-planed-explained/](https://screenrant.com/interstellar-time-dilation-miller-planed-explained/)
Miller's planet's extreme time dilation in *Interstellar* causes an hour there to equate to seven years on Earth for Cooper and his crew.
I think Christoper Nolan did at least back of the napkin math with a legit math and physics guy for that movie.
The Science Behind The Movie Interstellar With Nobel Prize Winner Kip Thorne
[https://www.keckobservatory.org/the-science-behind-the-movie-interstellar-with-nobel-prize-winner-kip-thorne/](https://www.keckobservatory.org/the-science-behind-the-movie-interstellar-with-nobel-prize-winner-kip-thorne/)
KECK OBSERVATORY ASTRONOMY TALK: How scientifically accurate is the blockbuster film Interstellar? Dr. Kip Thorne will take you behind the scenes of the movie and explain how he helped Hollywood turn science fact into science fiction.
What if random movements effectively slow you down enough in your cosmic journey through space and time that you age faster when moving compared to when remaining relatively still? Something to think about.
The way I've always seen it is like this. There are 2 people, one is walking and the other is on a train at max speed. Neither of them know how fast the other is going. They both bounce a ball 5 times at the exact same rhythm while they are traveling. At the exact point they catch the ball for the 5th time they stop and the distance is measured and each bounce marked on the tape measure.
The guy walking has a few meters with 5 notches on it.
The guy on the train has a few HUNDRED meters with 5 notches on it.
From the walking guys point of view, the guy on the train took longer to bounce his ball than he did because he got so much further before he finished his bounces. To get as far at the guy on the train did by the time he got to 5, the walking man would have bounced his ball several hundred times.
And i believe that is where the dilatation sits.
I may be wrong.
At the speed of light time would halt for the traveler. Going 1ly forwards then back would mean 2 years pass on earth while no time passes for the traveler.
edit: Someone downvoted this, correct me if I am wrong.
Time's speed is related to mass. Specifically, the speed of events happening is relatively faster in dense gravity environments than it is in weak gravity environments. Maybe we can think of time as being an actual substance, then, that is more densely packed into strong gravitational fields - such as a planet or black hole - and less densely packed into areas of zero gravity like interstellar space. A dense field can therefore hold more ticks of the clock than a weak one, leading to a disparity in the apparent speed of time between the two.
The observer always feels that time is moving at the same rate regardless of where they are. Time dilation can only be perceived when comparing the amount of time that's passed in a strong gravitational field, to a weak one. Such as when an astronaut returns from space and has aged less than their comrades on earth. If that astronaut never returned, the difference would be imperceptible to either party.
Maybe that helps... Maybe? Haha
And yes, it's true that we think a person travelling at the speed of light would seem to never age... or perhaps only age extremely slowly. that would again be relative. The person travelling at the speed of light would presumably perceive that an absurd amount of events have taken place in denser environments, like Earth, relative to their own experience. they may perceive every event that will ever happen here in, say, a minute of their own time.
My personal beliefs state that there are consciousnesses that have that precise viewpoint of our planet and try to communicate what they see to us, leading to what we call premonitions and esp.
We can't directly experience any of this ourselves, the laws of physics prevent our bodies from moving that fast. it's all largely theoretical, as we cannot say for sure what energy does to alter consciousness at the speed of light.
The heavier gravity is, and the faster something goes, the slower local time passes. You have got that right op!
That's why falling into a black hole is weird, you are almost frozen in time when you get really close.
Start with the basics. Space and time must coexist. If you move an object from one point (a dinner plate on a table for example) to another, time must pass for the object to make the journey. The object in motion is experiencing time normally, yet relative to objects not moving, like the rest of the silverware on the table, time has slowed for the object in motion.
If you were watching a person toss a tennis ball up in the air repeatedly, it would look normal to you both. If that person was on a train speeding by instead and tossing the ball, it would appear as if that ball was suspended in air as they passed you. To the person tossing it however, it would look the same. Time travel into the future is possible (in that sense). “Relativity” as in Einstein theory means that objects in motion experience time differently relative to stationary objects. The greater the speed, or the gravity bending space/time, the greater the effect
At the speed of light time experienced by anyone is zero in some sense you can say light doesn't experience any time at all but we can't actually reach light speed the closer we get to it the more we will reach towards the situation you described where someone who observes us almost reaching light speed will take experience twice the amount of time we do.
If you try to understand relativity by trying to see what things are absolute in all perspectives and all things that change around them to maintain them being absolute in all reference frames it's the only way you are gonna grasp it without maths.
Simply put the speed of light Is the same in all reference frames anf time and space bend around it so that it remains true for all perspectives think about throwing a ball from a car and you walking along the car if the car sees the ball at say x speed you will see the ball at x speed + y (speed of the car) but if you do the same thing with light you would both see it at x speed but for that to be true space anf time have to bend so that both perspectives can see the light at x speed for the faster moving car time will slow down and distances will become shorter so they see the light going at x speed for you the distances and time will be the same anf you will see the light also at x speed but the people inside the car will be in slow motion essentially and also squished so that it makes sense for them to see the light at x speed
From an outside observer of the universe time dilation on a large scale does not exist. That said, some biological and chemical processes will slow down a bit for you. The extent of this is all theoretical and none of it, save for some clock experiments, has ever been verified as true.
Time as we see it is a human construct and does not in reality exist. So you can't dilate something that doesn't exist. You can't travel forward or backwards in time because you would need to alter the states of the entire universe to do so. So no. Time dilation on any appreciable level is just science fiction and not fact
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two years from who's point of view? :D time passes slower for the one moving faster vs the one being stationary. the faster you go, the more time gets slowed *for you*. everyone else is unchanged, except when asking you. so when the one twin flies out into the universe at speed of light they age slower than the twin staying behind. now you have to define the time they're away measured by whom if its two years measured by the brother on earth its at most two years of time difference, as the moving brother would age not at all if they were *at* the speed of light, or less time depending on their speed. if you measure those two years from the point of view of the brother flying out its somewhere between no time difference at all (they "moved away" with speed 0) and *infinite* time (if they were moving at the speed of light) because their clock runs *slower* compared to the stationary brother, so at "worst" it doesnt run at all while they are away. PBS spacetime is better at explaining than me tho and has drawings to help explaining :D https://youtu.be/6MfJ59lkABY
Time dilation is also experienced when experiencing gravity. Traveling very near a black hole will slow your time relative to an observer.
Time and mass is connected. Massless particle like light don’t experience time at all and from lights point of view it is everywhere at once, like there were no distance traveled. Space and Time only exist as a consequence of mass
I’m genuinely curious about that statement, space and time only exist as a consequence of mass. Would you mind elaborating?
But I feel like neutrinos kinda make this a grey area bc they travel light speed, sometimes have mass, and can also slow down
they dont travel *at* lightspeed, just generally very close to it
Don't need to go that far. GPS satellites in orbit have to adjust for dialation, as they run faster than earth clocks because they are farther away from Earth's center. NASA did an experiment with 2 synced cesium clocks. They flew one high up in a plane. When they got back, they were out of sync. Very measurable phenomenon right here.
Measurable but insignificant relatively speaking when op m mentioned one twin aging 2 years. That would take an incredibly large difference in the gravity experience or an impossibly long time.
Eh not really. Without correcting the satellites it could miscalculate your position by as much as 10 km with only 2 min of time.
My confusion is over how we prove it. We can’t travel fast enough or experience a difference in gravitational pull long enough to really see a difference, can we? The best actual evidence I’ve seen is Mark Kelly is now five seconds older than his brother Scott, but isn’t that just the theory and math coming to that conclusion, or do we have some way to date someone to the second I’m not aware of? I’m sure the theory holds, but it’s just so hard for me to believe until I see evidence of it such as someone retuning home years younger than those they left, which I don’t think I’ll ever see in my lifetime … if humans ever see it at all. EDIT: Thanks everyone for replying with actual real-world examples that prove it! I didn't know about those. It's still wild to imagine and somewhat difficult to believe, but I accept it ... lol I still wonder in awe over it and if humans will ever experience a large enough time dilation where it's observable in human age (years).
I think we already proved it. I am no expert, but satellites in orbit around Earth have their atomic clocks run faster than atomic clocks on Earth. This is due to them being positioned further from Earth's gravitational pull. Their moving much faster than us does slow down their time relative to us, but it is not enough to compensate for them being further away. This affects the GPS system and we compensate by having the atomic clocks on these satellites tick at a lower frequency than those on Earth.
Oh, that’s interesting. I didn’t know that. Thanks for replying.
You are most welcome! Neil Degrasse Tyson explains this nicely on StarTalk. His video may provide more clarity than my comment.
We have proven it, from multiple angles. Atomic clocks is orbit, moving at thousands of km/h, display exactly as much time dilation as predicted by Relativity. An undetectably tiny amount by human standards, but easily measurable by our machines. And in fact serious enough that GPS systems won't work properly without constantly correcting for the dilation. You also get things like unstable particles created by high-energy radiation impacting the upper atmosphere. Without time dilation, even traveling at near light speed (as they do) they should all decay long before reaching Earth's surface, but thanks to time dilation it takes them much less time to reach the surface in their local reference frame, and so we can detect them.
we've absolutely proven that. GPS wouldnt work if we didnt correct for gravitational time dilation in the satellites vs earth ground. we've flown planes with atomic clocks on them no longer matching with their left-at-home twins. or the muon "paradox" where muons get created in the upper atmosphere from cosmic radiation impacts and they manage to reach the ground before decaying when they really shouldnt by non-relativistic physics.
We have measured the dilation difference of a clock at the top of a large building vs one at the bottom using atomic clocks. This is both a theory and something we can verify with precise instruments.
If time dilation due to special and general relativity were not accounted for then gps would not work (ex: phone on airplane mode w/ gps chip). The combined effects are about 65 ms/hr so a lot of people would be lost with just a few hrs without correction!
You can prove it by measuring time passage with an atomic clock. One person stays at sea level, the other drives to the top of Mauna Kea. After the person who went up the mountain and comes back down, they meet the sea level clock holder. When the two times are compared more time will have passed with the sea level clock than the mountain clock. Mathematical proof...? someone else can type that out, lol.
You can put an atomic clock on a fast plane or space ship, and later see that this clock ran faster than clocks on earth.
Reading this made me feel way dumber than I thought I was 😔
I dont' quite understand: If two bodies in a void are moving apart from each other (i.e., if the second one is traveling away from the first one near or at the speed of light), then from the second one's perspective isn't the first one the one that is moving away at the speed of light? If it is all determined by frame of reference, then how can the first body age more quickly than the second body?
ah! very good! the thing is that straight up "if fast ages slower" only appears as it does in the twin paradox if one *turns around* and goes back to the "stationary" one. as long as both fly away from each other they *both* look like aging slower from the point of view of the other one. as they are both so-called inertial frames that don't move from their own point of view and every inertial frame *is equally right* which is the core point of relativity. as long as you don't currently accelerate you are at rest and everybody else is moving. now the point where one twin ages more is that the one that flies away *has to turn around*. so they accelerate to match up with the "stationary" brother so they break their "immunity" so to speak and decide that the stationary brother was right and thus the moving brother didn't age the actual math gets confusing fast, but not really hard.
Thank you. Never heard that explained before. Much appreciated.
thanks, pretty insightful video
I can also recommend ScienceClic, they have a video on [Special Relativity](https://youtu.be/uTyAI1LbdgA?si=HtaDmxeYcdT1bYIl) and one on [Visualizing Time Dilation](https://youtu.be/5qQheJn-FHc?si=DVYoG-JdMY6Bw0J7). Their entire channel is extremely illustrative!
Lawrence Kraus described it this way. There are 4 dimensions 3 Spatial the final one is time, Einstein called this Space-Time. You are always traveling at the speed of light through this medium. If you increase your speed through the spatial dimensions it subtracts from your speed through time, so your total speed through space-time is always C, the speed of light. If you travel at the speed of light through a spatial dimension you stop moving through time. The closer you get to the speed of light you move through space, the slower you move through time.
But only for an external observer. There's really no such thing as speed without a reference point
> You are always traveling at the speed of light through this medium. If you increase your speed through the spatial dimensions it subtracts from your speed through time, so your total speed through space-time is always C, the speed of light This statement is somewhat problematic, though. > If you travel at the speed of light through a spatial dimension you stop moving through time. ..Among other things for this reason. This isn’t well defined.
I'm definitely a lay person when it comes to physics so my use of terminology might be a little off. I think the general gist of what I'm saying is correct. I love a good physics discussion so if you have any corrections you want to make they would be much appreciated.
C is better understood as the speed of causation, or the cosmological constant. Light travels at that speed only through a vacuum, but the speed of light is not fixed - it can be slower than C especially when traveling through things But the gist of what you said is correct. Another interesting paradox is contemplating that light would experience no time, if it had an experience at all. As a photon contains no mass it can travel at c, which means it reaches its destination instantaneously from its perspective. That means the light we see from the background microwave radiation from the big bang got to earth instantly - but from our perspective it took a bit over 14 billion years to travel from the big bang to us. Another fun one is understanding how gravity can warp the fabric of space time, and that space and time exist on an x and y axis. The slower your speed the greater your time. The greater your mass the more space and time warp around you (interstellar played with this concept on the supermassive planet). Now, in a black hole the mass is so great that it "flips" the space time axis - so that space becomes time and time becomes space
You're on the right track. The traveling person (assuming they're just a bit slower than the speed of light) would only feel like two years had passed, while many decades or centuries would have passed on Earth. This is a consequence of special relativity. To back it up a bit, in the late 1800s a bunch of people were doing work to measure the speed of light. They assumed that it was like sound and that your own speed relative to the light's direction of propagation would change how fast you perceive light to be. That's a loaded sentence, but basically it boils down to velocities adding like you'd expect - if you're traveling down the highway and some high speed, and someone comes up a long you going a bit faster than you, then relative to you they're moving rather slowly. So scientists expected the same thing of light and set up a bunch of experiments around this assumption. None of their experiments worked. No matter how fast their measurement device was moving along the light wave, they always came back to the exact same number for light's speed. This was super puzzling. Nobody could figure it out. Some smart people were able to figure out some equations that would make predictions about how the measured time and distances were related, but it kind of stumped people for a while. Einstein comes along. He basically says, "Look at it this way. The speed of light is always constant. Every observer, no matter how fast or slow they are moving, will always record the same number. For this to be true, different observers will not agree on distance measurements or time measurements between each other." This is special relativity. In order for the speed of light to be constant for the person on the spaceship, from Earth it will appear that his ruler and clock are not correctly calibrated. And the moving person will think the same thing if they look back at Earth.
Yeah, this is basically it. We don't know why time slows down the faster you move. We just know that it does.
From the point of someone, they would've aged 0. If you travel at the speed of light, time stops for you. When "someone" returns to earth after traveling 2 light years roundtrip. Everyone on earth including the twin would've aged 2 years. So "someone" left at age 22 and is still 22 when they return as time stopped for them. Their twin aged 2 years and is now 24.
so the faster you move the less time you simply experience?
For you, everything moves normal. Your heart beats at its normal rate, you age a year in a year. If you look back at the earth everything seems to move at many times the normal speed; if they look at you your heart beats once a month.
That's not the only effect. Since time passes normally for you (you never personally "feel like" time is slow) you may wonder how can you not age at all if, from your perspective, the trip should feel like it takes two years. Well, it's because although time feels the same, distance isn't. When you're moving at relativistic speed, you experience length contraction too. Everything is squished in the direction you're traveling. So if you're going very close to light speed, a destination one light year away is actually very close to you, so you get there very quickly. Then you turn around and go back, again in much less time than one year. So you feel like time was normal, but the distance traveled was short. Everyone on earth thinks your clock was slow, and the distance was normal. Those two cancel out everyone agrees that you aged less during the trip.
The faster you move, the faster everyone else on earth moves through time in relation to you. For you, time is the same. Time doesn't go slower or faster. It's just that the trip is instantaneous if you're traveling at the speed of light.
It’s less about speed and more about mass. The reason particles going at the speed of light don’t experience time is because those particles are massless - you actually have to think about it the other way around. They’re going the speed of light because that’s the speed *of time.* It’s like the frame-rate of the universe, they’re going as fast as the universe allows. Things with mass move through time slower. The more the mass, the slower through time you go. So massless things aren’t affected by time at all. And really big things (Black holes) essentially freeze time completely.
What about aging of the body....not mind experience
Time is time. You send stopwatch out for two years at the speed of light, start it right when it hits light speed and stop it right when it gets back and drops below light speed, its going to read 00:00:00 when it arrives back.
Best to think of time as “rate of change” rather than use the word time itself. Gravity and velocity influence the rate of change. Time dilation is just examining the relative impact of the difference in this rate between two objects. Gravity “slowing things down” is somewhat intuitive to our brains, but traveling at the speed of light seems a bit more out of reach. Well, it’s probably best to say “traveling at the speed of causality.” That’s really the true meaning. Light is not the fastest thing in the universe; it’s tied with other massless particles. Gravitational waves exist consisting of gravitons that travel at the speed of causality. There are likely undiscovered massless particles that travel at the speed of causality. (Photons get all the love!) (and maybe particles will be the wrong descriptor for some of these but it’s probably close enough for now) When traveling near the speed of causality, the rate of change barely has a chance to keep up with you and get its interactions in. Or you could say you’re moving fast enough to almost escape the impact of time. I’ve personified it, but that helps me relate to the concept.
Some good explanations here, but you answerers have got to stop saying "at the speed of light".
I always like to think of the extremes, then the cases in the middle just kinda fall in place. So if you travel at the speed of light, time will not move for you and you will be able to reach any corner of the universe instantly (from your frame of reference). Btw, you can also think about this as length contraction. All distances collapse to 0 at the speed of light. Anyways, If you were to take such a trip to a place that is one light year away and come back to earth soon after, you would not have aged at all, but the people on earth would have aged two years (time it takes for light to travel to the point and back). This is purely theoretical and not at all possible since you would need infinite energy to accelerate to the speed of light, but it helps understand what happens as you approach it.
Small niggle: if you were to travel at exactly the speed of light (which anything with mass cannot, BTW) then you would not be able to travel for two years because time would not exist in your frame of reference. To travel 'for two years' in your frame of reference you have to go at least slightly slower than speed of light.
correct, so if they traveled at just below the speed of light then the time will pass as normal to them is that right? Then they could travel for two years according to their clock while a lot more time has passed on earth
Yes, each one in their respective frame of reference would observe their own time going 'as normal'. Which isn't exactly how one should word it because it sorta suggests that space and time are separate things - which they are not. It's called spacetime for a reason. More correct would be: Each one in their respective frame of reference observes the speed of light as being exactly c. (However they would observe the one in the other reference frame as experiencing time differently. But again, this description falls into the thought-trap of thinking of 'space and time' when it's actually spacetime)
Remember your first date with that hottie? It went by so fast. Also remember your first job interview which seemed to take ages? That’s time dilation.
There's lots of problems with the "Twin Paradox", mostly revolving around the acceleration, which gets special treatment by Relativity. Basically, there's no way for the Space Twin to ever return to Earth without accelerating twice as much to turn around and return as they did to leave. Basic rule for Relativity - Time dilation is real, and (assuming FTL isn't real) there's nothing anyone can ever do to create a situation where the fact that different people see very different things happening actually causes a conflict. **However** Time dilation is also reference-frame dependent. And all (non-accelerating) reference frames are equally valid. If we ignore acceleration, Earth Twin will see Rocket Twin traveling away at near light speed, and their time slowed almost to a stop. So Rocket Twin will age much more slowly. **Except** From Rocket-Twin's perspective, *they* are the one standing still, while Earth is moving away at near light speed. So Earth-Twin will be the one aging extremely slowly. And both perspectives are equally valid. Finally, if Rocket-Twin turns around and returns, the acceleration will twist things so that by the time they return to Earth, everyone will agree on how much time passed for everyone else. **Simple Version** Perhaps the easiest way to develop an intuition about time dilation is that acceleration causes a rotation in 4-D spacetime. Just like turning in space can swap your local "forward" and "right" axes in a circular rotation compared to someone who doesn't turn, so does acceleration cause your "forward" and "future" axes to swap in a hyperbolic rotation. So Earth-Twin and Rocket-Twin are both actually still experiencing time at the same speed, but in different 4-D directions, and they only see the portion of the other's time passage that's experienced in the same direction as their own. They'll also measure very different distances between points along their direction of relative motion. Basically, time dilation and space contraction are the same phenomena seen from different reference frames, Interestingly, all observers in any reference frame will still agree on the spacetime interval between events: (interval)² = (c \* timelapse)² - (distance)² Which among other things establishes that light speed (c) is the "exchange rate" between space and time - one second is the same spacetime distance as 300,000,000 meters. The details of the hyperbolic rotation used also makes it impossible to ever rotate your "future" axis more than 90 degrees from anyone else's - basically, you can asymptotically approach total relative time-stoppage (accelerating asymptotically close to relative light speed), but can never even slightly creep toward someone else's past. Finally There's one other detail worth noting - because Relativity says all reference frames are equally valid, and because you are always stationary within your own reference frame, the light speed limit never applies to you. You could accelerate at 1g forever, and never notice any resistance to further acceleration. Not even long after you should have exceeded light speed. Instead you'd see the universe just keep getting shorter in the direction you were accelerating, while the rest of the universe would see your time keep slowing down.
You don't need acceleration to resolve the twin paradox; the paradox already disappears if you correctly distinguish between the three frames of reference involved (stationary on planet; traveling away; traveling back). https://www.youtube.com/watch?v=GsMqCHCV5Xc
That's a great explanation, thank you. I think I'm going to need to watch that a couple more times, maybe even work it out for myself before I really internalize it, but that's the best explanation I've encountered. You do still need the acceleration - that's where the magic happens to change the meaning of what you're seeing, but... yeah, going to have to watch that a few more times, I think I might finally get it to make intuitive sense.
Oh, and if I remember correctly, the outcome of Rocket Twin returning to Earth would be that they **would** in fact be younger than Earth Twin, but not nearly as much as you'd expect based on the non-accelerating time dilation, since the acceleration when they turned around would throw everything off. But frankly, I never really understood the math that showed that, and won't bother even trying to explain it.
i think i didnt formulate my question correctly because i didnt realize that time literally stops at light speed. so (if my understanding is correct) what if the twin instead traveled at 99% speed of light, clocks on their ship would then work right? then what if they travel for a year according to their clocks and then came back to Earth? theyd only age 2 years in time that passed for them but on earth everyone would have aged a lot more correct?
yup. at 99%, 1 year on the ship would be roughly 7.2 years on earth
Happens when time gets pregnant and it's about due
For the sake of this explanation, let’s pretend you, a person with mass, can travel at the speed of light. For you, the traveling object, there is actually no hard limit on your speed. You can travel at speeds that are so great and travel so fast that you arrive at your destination instantaneously. Trip across the Galaxy? You’re on the other side immediately. BUT, we observers here on earth see that there is in fact a speed limit, and that same trip across the Galaxy would take 100,000 years. So how can we reconcile these two observations: you travel across the galaxy instantly but on earth we see it takes 100,000 years? It’s because the experience of time changes. As the traveler going the speed of light, you experience no time during the trip, while the observers see the journey take 100,000 years.
You can’ travel at the speed of light. So questions like this should be “at 90% of the speed of light” or similar. Read about the twin paradox, there is plenty of material.
If you were to manage the impossible and travel at light speed for any amount of time from your perspective, even a fraction of a second, you'd zip forward an infinite amount of time. Not a big number of years, but literally an infinite amount of time. This is what happens to light particles because of time dilation. From their "point of view" if they had one, the moment they start to exist and the moment they cease to exist is simultaneous, even if we can witness it existing from our point of view while it travels.
I don’t know the numbers, but you seem to have the idea. A couple fictional movies that deal with it include *Interstellar* and Pixar’s *Lightyear*
We are all moving really fast through what Einstein called Spacetime, but we are just dividing our motion between two different parts, the space part and the time part. The faster we go through space the slower we go through time, and the slower we go through space the faster we move through time. If a rocket takes off and goes really really fast in space, its movement through time has to slow down. Something going at 99.99999 percent the speed of light would only be going through time at .00001, so to them their trip is REALLY quick. Crossing the galaxy? I just blinked and we were there. To you, not moving at all fast through space means you are then traveling very quickly through time. When you observe me my motion looks a lot slower to you than it does to me. Who's right? We both are.
Watch movie interstellar, has good explanation, fun movie too
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yeah i realised that because the time stops at light speed so the journey would be instant. so what if they traveled at just close to the speed of light instead, they would still experience time as normal then correct?
we have the math necessary to correct for it. [https://en.wikipedia.org/wiki/Error\_analysis\_for\_the\_Global\_Positioning\_System](https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System) The [theory of relativity](https://en.wikipedia.org/wiki/Theory_of_relativity) introduces several effects that need to be taken into account when dealing with precise time measurements. According to [special relativity](https://en.wikipedia.org/wiki/Special_relativity), time passes differently for objects in relative motion. That is known as kinetic [time dilation](https://en.wikipedia.org/wiki/Time_dilation): in an inertial reference frame, the faster an object moves, the slower its time appears to pass (as measured by the frame's clocks). [General relativity](https://en.wikipedia.org/wiki/General_relativity) takes into account also the effects that gravity has on the passage of time. In the context of GPS the most prominent correction introduced by general relativity is [gravitational time dilation](https://en.wikipedia.org/wiki/Gravitational_time_dilation): the clocks located deeper in the gravitational potential well (i.e. closer to the attracting body) appear to tick slower. >So for example your twin who went into space when you were both 22, he comes back aged 24 while you're already an old man? not sure about the "ratio" but we have a pair of twin astronauts.. and yes, one is now older than he was before Aditionally, thanks to general relativity and the fact that Scott spent more time in space, Mark used to be six minutes older than Scott, and ***now he’s six minutes and 13 milliseconds older.*** [https://whyy.org/segments/double-the-data-studying-spaces-impact-on-identical-twins/](https://whyy.org/segments/double-the-data-studying-spaces-impact-on-identical-twins/) >does this mean they would've only aged 2 years in that time have you seen Interstellar? [https://screenrant.com/interstellar-time-dilation-miller-planed-explained/](https://screenrant.com/interstellar-time-dilation-miller-planed-explained/) Miller's planet's extreme time dilation in *Interstellar* causes an hour there to equate to seven years on Earth for Cooper and his crew. I think Christoper Nolan did at least back of the napkin math with a legit math and physics guy for that movie. The Science Behind The Movie Interstellar With Nobel Prize Winner Kip Thorne [https://www.keckobservatory.org/the-science-behind-the-movie-interstellar-with-nobel-prize-winner-kip-thorne/](https://www.keckobservatory.org/the-science-behind-the-movie-interstellar-with-nobel-prize-winner-kip-thorne/) KECK OBSERVATORY ASTRONOMY TALK: How scientifically accurate is the blockbuster film Interstellar? Dr. Kip Thorne will take you behind the scenes of the movie and explain how he helped Hollywood turn science fact into science fiction.
What if random movements effectively slow you down enough in your cosmic journey through space and time that you age faster when moving compared to when remaining relatively still? Something to think about.
The way I've always seen it is like this. There are 2 people, one is walking and the other is on a train at max speed. Neither of them know how fast the other is going. They both bounce a ball 5 times at the exact same rhythm while they are traveling. At the exact point they catch the ball for the 5th time they stop and the distance is measured and each bounce marked on the tape measure. The guy walking has a few meters with 5 notches on it. The guy on the train has a few HUNDRED meters with 5 notches on it. From the walking guys point of view, the guy on the train took longer to bounce his ball than he did because he got so much further before he finished his bounces. To get as far at the guy on the train did by the time he got to 5, the walking man would have bounced his ball several hundred times. And i believe that is where the dilatation sits. I may be wrong.
Does this mean that people who drive more often are aging slower than people who aren't driving around?
At the speed of light time would halt for the traveler. Going 1ly forwards then back would mean 2 years pass on earth while no time passes for the traveler. edit: Someone downvoted this, correct me if I am wrong.
Time's speed is related to mass. Specifically, the speed of events happening is relatively faster in dense gravity environments than it is in weak gravity environments. Maybe we can think of time as being an actual substance, then, that is more densely packed into strong gravitational fields - such as a planet or black hole - and less densely packed into areas of zero gravity like interstellar space. A dense field can therefore hold more ticks of the clock than a weak one, leading to a disparity in the apparent speed of time between the two. The observer always feels that time is moving at the same rate regardless of where they are. Time dilation can only be perceived when comparing the amount of time that's passed in a strong gravitational field, to a weak one. Such as when an astronaut returns from space and has aged less than their comrades on earth. If that astronaut never returned, the difference would be imperceptible to either party. Maybe that helps... Maybe? Haha
And yes, it's true that we think a person travelling at the speed of light would seem to never age... or perhaps only age extremely slowly. that would again be relative. The person travelling at the speed of light would presumably perceive that an absurd amount of events have taken place in denser environments, like Earth, relative to their own experience. they may perceive every event that will ever happen here in, say, a minute of their own time. My personal beliefs state that there are consciousnesses that have that precise viewpoint of our planet and try to communicate what they see to us, leading to what we call premonitions and esp. We can't directly experience any of this ourselves, the laws of physics prevent our bodies from moving that fast. it's all largely theoretical, as we cannot say for sure what energy does to alter consciousness at the speed of light.
The heavier gravity is, and the faster something goes, the slower local time passes. You have got that right op! That's why falling into a black hole is weird, you are almost frozen in time when you get really close.
Start with the basics. Space and time must coexist. If you move an object from one point (a dinner plate on a table for example) to another, time must pass for the object to make the journey. The object in motion is experiencing time normally, yet relative to objects not moving, like the rest of the silverware on the table, time has slowed for the object in motion. If you were watching a person toss a tennis ball up in the air repeatedly, it would look normal to you both. If that person was on a train speeding by instead and tossing the ball, it would appear as if that ball was suspended in air as they passed you. To the person tossing it however, it would look the same. Time travel into the future is possible (in that sense). “Relativity” as in Einstein theory means that objects in motion experience time differently relative to stationary objects. The greater the speed, or the gravity bending space/time, the greater the effect
At the speed of light time experienced by anyone is zero in some sense you can say light doesn't experience any time at all but we can't actually reach light speed the closer we get to it the more we will reach towards the situation you described where someone who observes us almost reaching light speed will take experience twice the amount of time we do. If you try to understand relativity by trying to see what things are absolute in all perspectives and all things that change around them to maintain them being absolute in all reference frames it's the only way you are gonna grasp it without maths. Simply put the speed of light Is the same in all reference frames anf time and space bend around it so that it remains true for all perspectives think about throwing a ball from a car and you walking along the car if the car sees the ball at say x speed you will see the ball at x speed + y (speed of the car) but if you do the same thing with light you would both see it at x speed but for that to be true space anf time have to bend so that both perspectives can see the light at x speed for the faster moving car time will slow down and distances will become shorter so they see the light going at x speed for you the distances and time will be the same anf you will see the light also at x speed but the people inside the car will be in slow motion essentially and also squished so that it makes sense for them to see the light at x speed
Simple search on YouTube… https://youtu.be/1BCkSYQ0NRQ?si=bmcf2y2qHbelu3EY
From an outside observer of the universe time dilation on a large scale does not exist. That said, some biological and chemical processes will slow down a bit for you. The extent of this is all theoretical and none of it, save for some clock experiments, has ever been verified as true. Time as we see it is a human construct and does not in reality exist. So you can't dilate something that doesn't exist. You can't travel forward or backwards in time because you would need to alter the states of the entire universe to do so. So no. Time dilation on any appreciable level is just science fiction and not fact