Suppose that on Planet X, one hour there is equivalent to 10 years on Planet Earth.
But certain events, as a matter of practicality, must still be the equivalent in Earth-time, right? It’s not really meaningful to say it’s slower there?
For instance: If you detonate a block of explosive TNT on Earth, that thing detonates pretty much instantly. Let’s say it takes 0.1 seconds for the thing to blow up on Earth.
But when you set off that same block of TNT on Planet X, it also detonates pretty much instantly (it has to…that’s how explosives work). Yet by Earth standards, that block of TNT took much longer to explode.
Does that mean that if we had some sort of super-telescope on Earth and we could watch that same block of TNT explode on Planet X, that we would be watching an extremely slow-motion explosion unfold over the course of, say, several hours?
Not really; physics is not [supposed to be] locally different, but when you look at distant objects through a telescope, they are moving away from you at high velocity so what you observe is a redshift:
so clocks appear to tick slower, or explode more slowly Note the remote observers also see the same thing re events on Earth, yet you would not say events on Earth are happening in slow motion.
I haven’t seen Interstellar, but time dilation only becomes big near the speed of light. Neither a planet or a star can be massive enough to have major time dilation. Even on a neutron star (which has an escape velocity around half the speed of light) time runs only around 15 percent slower than on Earth.
In Interstellar, the planet itself wasn’t that massive; it was just very, very close to a black hole. In principle it could happen, but good luck getting to or from there with any remotely plausible space travel technology.
In any given frame of reference, time seems normal for everyone in that frame of reference, because time dilation affects time itself, not any specific way of measuring it. If you measure time with your pulse, or with a mass oscillating on the end of a spring, or with light bouncing back and forth between two mirrors a fixed distance apart, or by the oscillation of quartz crystal, or whatever, if those match anywhere, they’ll match everywhere. It’s only when you compare the two different planets that you ever notice anything. And yes, an observer on Earth watching that planet, if they can manage it at all, will see everything on that planet (clocks, aging, explosions, whatever) all happening in slow motion.
Due to the high gravity (~67 billion times that of Earth) on the surface of a neutron star, time for an observer on the neutron star would pass more slowly relative to an observer far away from the neutron star. This is a result of gravitational time dilation (from Einstein’s theory of General Relativity).
In the book “Dragon’s Egg,” the Cheela experience time at a much faster rate than humans because their biological processes are incredibly accelerated in their high-gravity environment. One second for humans is equivalent to many days for the Cheela.
The high-gravity environment of their neutron star home compresses matter to such an extent that the Cheela’s life processes, based on nuclear interactions, occur on a timescale millions of times faster than those of humans, whose life processes are based on electron interactions.
It is called relativity because it is just that, relative to an outside observer. Nothing on Planet X is happening faster to those who are there, at all. There is no speed difference, no time difference, time is happening at the same rate for them as it is on Earth.
The observed difference is due to the relative speed of both places. That causes an apparent difference in time between the two places.
May seem faster, may seem slower, relative to where you are, but both sites are passing time at the same rate.
The appropriate way to look at this is that time is fundamentally just a way of measuring intervals between events. So everything, right down to the subatomic level, conforms to the flow of local time, which may be much faster or much slower than the flow of time in a different frame of reference.
Right. The “speed up” factor of nuclear versus chemical reaction time more than counteracts the effects of gravitational time dilation (which would have events on the surface of the neutron star going slower than events outside.
Please excuse me going off on a tangent and asking a probably stupid question, but does this mean that if the earth wasn’t orbiting our sun, and our solar system wasn’t orbiting the center of our galaxy, etcetera, time would not exist for us at all?
Or would it still exist for us but not be apparent to an outside observer?
If you are on slo-mo planet you will not notice that. A second on slow-mo planet is the same to you as a second on fast-mo planet.
Same with the explosive. To a person standing on slo-mo planet the explosion happens every bit as fast as it does on fast-mo planet. The watch on slo-mo ticks slower but so does everything else. To you, standing there, the explosion happens every bit as vigorously as it would anywhere else.
The thing is, to some outside observer at a distance, they see it happen in slo-mo.
No reference frame is preferred. It’s just where you are that makes the difference.
There is no “not moving.” It is an impossible thing to discern. There is no rock in space that says, “This rock is not moving. - God”
Imagine you are in a universe with seemingly nothing else in it. Then, you see something coming towards you. It flies by you. So, now there are two things in the universe.
Which one of you is still and which is moving? It is impossible to say. From each perspective they are the still one.
ETA: There is no experiment you could do to decide who is still and who is moving (or some combination).
In special relativity, it all stems from that. In general relativity, which deals with gravity, you also need a few other details like the equivalence principle.
One can certainly ask some pretty theoretical questions, but it seems to me that if there is a planet or even any place at all for observers to observe from, that we are already assuming this takes place in a universe, with normal 4-d geometry including space and time.
The point is that maybe both observers think the other one is the slo-mo planet. Or maybe you could set things up so each one thinks the other is the fast-mo planet. Or there could be some “standing on the surface of a neutron star with the other observer in high orbit” situation like people have described.
Note the remote observers also see the same thing re events on Earth, yet you would not say events on Earth are happening in slow motion.