I rewatched “Interstellar” and the time dilation dilemma makes my brain hurt. If a change in gravity alters time then wouldn’t you feel a difference entering/exiting said fake planet?
In: Planetary Science
No, because time is relative. There is no baseline by which to measure it. Wherever you are is your time. The real issue is whether the gravity would crush you or not.
You feel time *locally*. Time always feels the same speed to you because, well, that’s sort of part of the definition of time.
Now, your time where you are may appear different to me, over here, but to you yours is normal and to me mine is normal.
This holds true at every step of the process, going deeper in or out of a gravity well.
While I love the movie, it’s still science fiction.
You would feel being squished into a meatball as your mass increased, that’s it.
You as an observer never feel or see time dilation. Your perception of time is always the same, but relative to other frames of reference, time passes differently. However it’s worth noting that what is depicted in Interstellar is wildly exaggerated. If it really worked like that then there would be significant dime distortion between the characters’ heads and their legs, or from one end of the ship to another.
Time, for you, doesn’t “feel different”, ever.
In your point of view, the rest of the universe is speeding up (when you “enter” the planet) or slowing down (when you “exit” it).
Your own time, for you, feels like it’s going just as it always has.
If you like, I can make your head hurt more by noting that the way GPS works is by having very precise clocks on satellites orbiting the Earth. But because of the difference in gravity between the surface of the Earth, and the satellites in orbit, the clocks have to run more slowly (by about 38 microseconds per day) in order to properly synchronize with ground-based clocks to make the GPS system work. (Note that an error of 38 microseconds translates to *miles* of location error.)
[More information here.](https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps)
No. We cannot perceive time. None of our senses have an innate connection to time.
The only way we can perceive time is through secondary effects: watching things change.
Time dilation occurs only relative to someone else’s frame of reference. When you’re on the planet, time doesn’t go any faster for you, it only goes faster when compared to someone orbiting the planet.
The fundamental idea here is that time is not absolute, it can change, but only relative to other frames of reference. If you looked at the orbiting ship, it would appear to be moving very fast. If the ship looked at you, you would appear to be moving very slow. Each of you would see things near you moving at normal speeds.
The difference only becomes apparent when viewing a region of spacetime with a drastically different gravitational field.
One thing the movie doesn’t tell you is that for a large difference like this to occur (1 hour = 22 years?), the gravitational difference between the two regions would have to be massive. It would never happen the way it does in the movie. Brand and Coop would need to be essentially on top of the event horizon for a difference like this to manifest.
If I remember correctly, you only start to see drastic dilation when you’re very close to the speed of light (80% or greater for example). For something like this to happen, you’d probably need to be doing 99.9%, or whatever the equivalent gravitational gradient is.
Here’s a short animation that reviews relativity.
(Read below before watching for some frame of reference, so to speak)
My notes for you:
This is NOT an easy topic – and I don’t know if an ELI5 could even exist. More like ELI25… but having studied physics I can probably give a little info.
Let’s start with this…. As you go faster, your time moves more slowly than that of an observer. While YOU don’t experience it, more time will have elapsed for the person you left behind (the observer)). You come back to them, they have aged more than you.
It’s not actually the SPEED that’s causing the time dilation, rather the ACCELERATION. (I know you asked about gravity, stick with me here)…
So, as you accelerate, **your time is moving more slowly**. *(And for BONUS fun, check this out… as you approach the speed of light… that is to say, accelerate towards the speed of light,.. not only does your TIME slow down, but you also become more MASSIVE… And if that’s not enough for your brain… You actually SHRINK in the direction you are moving. All to an outside observer. You feel nothing and experience nothing other than the force pressing against your back as you accelerate.)*
Wild stuff.
OK… Now, how does this tide to the MOVIE? …soon. Just one mote foundational brick:
Acceleration and gravity are indistinguishable forces. In fact, they are the **SAME force**. Gravity is YOUR mass accelerating downwards towards a more MASSIVE body. In the case of somebody standing in their house… That “more massive body” is the earth that they are accelerating towards the center of. The reason why they are not *going* to the center of the earth is because the floor stops them.
When you are in a strong gravitational field… It is *exactly* the same as fast acceleration. And in the case of a movie, enough acceleration… A.k.a. gravity… for their time to dilate significantly.
The presumption being their mothership is far enough away from the black hole as to not experience that same dilation, or not to that magnitude.
The movie is correct in the interpretation of General Relativity.
Whether you could get on a planet with such a proximity to a black hole is **another matter entirely**. But the physics… it’s actuate. In fact, Neil deGrasse Tyson guest started on a CinnemaSins video to corroborate (or refute) the science.
It’s a good watch. And far more fun than the first link.
I’m sure it’s an awful ELI5 I’ve written, but if you can accept this, then you may be able to grasp it:
As you accelerate three things happen… (1) time slows down, (2) you gain mass and (3) you shrink in the direct of movement. This is tested. It’s accurate. It’s insane. And beautiful – as science tends to be. 🙂
So long ad we understand that gravity and acceleration are the same force (with different causes) we can see how General Relativity can cause this dilation of time.
All that being said… to “understand” may aspects of physics… well, it may not be possible. Heck, look up Bell’s Theory / Bells Inequality. This is a insanely rested theorem that shows, with basically zero doubt that “non-locality” exists. And may not fry your brain quite yet, it if you descend into the about hole that is Quantum Physics, you will have your socks knocked clean off your feet.
That’s all I got for now. I can be clarify or share more details. Or even resources if you *would like to know more*.
Consider a very tall tower on earth..
Now take 2 identical clocks and place one on top of the tower and keep the other at ground level and let them sit for a bit.
If you go to the top of the tower and observe the clock there and then go to the bottom of the tower and observe the clock there, they will both act exactly like a normal clock, each tick measures one second.
However, after bringing them back together the clock from the top will be a slight slight amount behind the clock at the bottom! This is not in some change that happens to the clock, but the fact that one second at the top of the tower does not equal one second at the bottom of the tower.
This is because the top of the tower actually experiences time a bit more slowly than the bottom because the top of the tower experiences less gravity!
Now imagine the bottom of the tower is the gravity well (where gravity is higher) and the top of the tower is the ship (where gravity is lower). Both clocks/people will each individually experience one second per tick, as if they were both in the same place, but their seconds are not actually the same when you compare them. Crazy huh!
For this reason astronauts are actually a bit younger than their earth bound coworkers!
Your perception of time is always the same, give or take your boredom level of course ;). But in terms of relativity, the differences show up when compared to others, either their perception of you or your perception of them.
In the case of Interstellar, the astronauts all feel time going regularly, however an outside observer would see them looking basically stationary from a far enough distance (and a super telescope I suppose).
The part that really blew my mind is the idea that the first astronaut who came and explored had only been there for one cycle of the tides. I thought I had caught an error when they found the wreckage relatively in tact, but they sewed that one up nicely right away.
What a film and soundtrack.
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