I’ve been thinking about relativity where the passage of time depends on your velocity, but I don’t really understand what this means physically. I understand that the clocks of two different people traveling at different relative speeds will be different, but what does this really mean? Does this imply that time is a physical quantity, like energy, and that depending on your speed you have less of it? To make this more complicated, my understanding is that it’s not just clocks that will be different, it’s the actual “age” of physical things; ex: if I’m traveling at the speed of light I can go infinite distance and to me it would be like waking from a coma, I would have no memory of traveling at all, so as far as I was concerned it didn’t happen. I guess I just don’t really understand what this means about the physical nature of time; is it a tangible quantity like matter or is it more like a byproduct of something else and what we call “the passage of time” is just how we measure it (ex: if I heat up a gas and the atoms get more disordered then it’s entropy has increased, but I can measure temperature and use that as a proxy for entropy).
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There is no such thing as “Time” as an independent “thing”. There is no such thing as “Space” as an independent “thing” either. There is only Spacetime.
Spacetime has 4 dimensions (leaving out the theoretical ones from other theories), x, y, z, and t. If you want to know where you are in spacetime, you need those 4 numbers. T = time. So time is not it’s own “thing”, it is a dimension of spacetime.
As for time dilation, the simplest way to explain it (which isn’t TOTALLY correct but accurate enough to be useful) is one given by Brian Greene in his book The Fabric of the Cosmos.
You body is made of matter. Matter is energy, so we can say you body is made up of X energy. At rest, X energy is moving through the Time dimension of Spacetime (at the speed of light). Now, lets say you walk across the room. You are now spending Y energy to move through a different dimension of Spacetime (a spatial one, up, down, left, right, etc). Since energy can neither be created nor destroyed, the energy needed to move through that spatial dimension of spacetime has to come from somewhere. It comes from the energy that was being used to move you through Time, so before you moving through Time with X energy, now you are moving through time at X – Y energy, which is slower.
Time is a unit of measurement. Usually we measure things by how much time it takes for something to happen. We could also measure time as the interval between something happening.
An example would be 1 year is how long it takes for the Earth to orbit the sun. An orbit could be described as ~365.25 days.
The universe doesn’t care about time. It simply goes from one frame of existence to the next guided by the laws of physics.
As for timelines, or time travel. That cannot exist as the universe only ever exists in its current form. We can remember 3 days ago, but 3 days ago no longer exists because it has become today.
Time is something our little human minds made up… It’s affected by both gravity and speed… Time is good on Earth to make sure you know when your favorite TV show comes on, the rest of the universe, it’s no constant that we like it to be
Time is merely a measure of motion. You can base it on any regular movement – the sun across the sky, the hands of a clock, the radioactive decay of an atom, whatever. It isn’t actually a real thing in and of itself. When people say time goes slower as you speed up, what they mean is that the internal molecular motion of the thing going fast slows down.
Now, you can use time as a mathematical variable, and in some instances the formulas it is used in will correctly predict reality. But, like any mathematical formula, you can play around with them beyond the limits of the physical context where they actually work. Most of the fantastic and nonsensical theories about time travel are like this. Take formula A that works under conditions X to describe the real world, switch the conditions to impossible thing Y, then pretend that you can still translate that into a description of physical reality.
I think what your asking in what time is “physically”. You actually mean how to conceptualize time from an outside of time perspective.
When you think of something physical, you have to have an outside perspective, like you can see the whole of a rock, weigh it, touch it, etc.
You can imagine this for space-time as well. Imagine your like god or something, and you can see from a singular point, the big bang, time and space expands out like an infinite expanding cone. This would be the perspective of an being that exsist on a dimension in which space-time is nestled it. Just like how people are nestled in space-time.
You would see the past and the future in freeze frame without motion, and the 3 dimensional space is expanding out on the 4th dimension of time.
If you want to know what time -is-, well its a field in which particles, and their force counterparts, is affected and carried by. Kinda of like a elctro magnetic field with magents and electric motors. Then electromagnetism has an carrier particles, and the force of space time use to affect other stuff, which is the Higgs-Boson. Funny enoguh that’s where the name god particle comes from.
Time is the letter “t” on a spacetime diagram.
I know that sounds like an unsatisfying answer, but that’s the truth. Physics is definitely interested in exploring the nature of reality, however this nature is done by measuring and describing reality through a collection of indices by which we order the universe. One of those indices we just call “t”.
In fact, you could argue Physics does less to reveal the universe than to simply explain how the universe behaves how our indices demand, but no actual insight into those indices themselves.
Your question, while fair to ask, isn’t truly a “Physics” question. No gatekeeping intended, just new thought.
Alright, imagine you have a big, stretchy blanket. This blanket represents space-time, which is like a mix of space and time. When you put heavy things on the blanket, like planets or stars, it makes the blanket curve, just like when you put a heavy ball on your bed, it makes a dent.
Now, time is like the way we count how things change and move. It’s kind of like counting how many times you jump on a trampoline. But here’s the cool part: because the blanket is curved by those heavy things, time doesn’t tick the same way everywhere. It can tick slower or faster depending on how strong the curve is.
We can prove space-time exists with something called the theory of relativity, which is like a special way of thinking about how things move when they’re really fast or near something really heavy. Scientists have done lots of tests and experiments that show this theory is true.
In the universe, time helps us understand when things happen and in what order. Just like you grow older each year, everything in the universe goes through changes over time. We’re still figuring out exactly what causes time to work, but we know that it’s connected to space and how things move around. So, in a way, space, time, and everything in the universe are all tangled together like the threads in a big cosmic blanket!
(More advanced definition: Spacetime is one thing, not two. The universe has different properties, but just like you can’t separate the wetness and coldness from water to analyze them isolated, spacetime is kinda just its own thing with two properties)
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