Time and space are linked, and gravity affects the flow of time. More massive objects slow the flow of time down.
What is time then? Has there been any significant research into what time actually is, or how it works?
In: Physics
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This is a question that occupies philosophers as much as it does physicists.
From a mathematical perspective, you can think of time as being more-or-less similar to the 3 dimensions of space that you’re familiar with. In 3-D space you have 3 axes which are all at right-angles to one-another (and in mathematics classes are usually labelled x,y,z). The space that these axes describe is 3-dimensional because you require 3 numbers to define every possible position in it. E.g. x=1, y=5, z=4 would be a position in a 3-D space. Every other possible combination of x, y, and z is also a possible position. Adding a time dimension is like adding another axis, meaning we now have 4 dimensions: x,y,z,t (t for time) and we require 4 numbers to define a point. This point can now be said to describe a position in space *and* a moment in time.
There are loads of further questions that you can ask about what time is, though, as there are many features of time that make it seem special and unlike the 3 dimensions of space. For one, I can freely move in every dimension of space whereas time seems to flow in only one direction (from past to future). Similarly, things which were accessible to me in the past don’t seem to exist anymore (e.g. dinosaurs) but it doesn’t seem to be the case that walking in one direction for long enough will cause me to stop existing.
A popular theory which tries to answer these questions and explain these features is a thermodynamical one which says that the reason time seems to “flow” is that the universe can be in more or less “ordered” states. That is, the configuration of everything in the universe: atoms, particles, energy, etc can be messy and randomly distributed or neatly separated. The “past” corresponds to those states where things are more ordered and the “future” corresponds to those states where things are more disordered. It may not be particularly clear what I’m getting at in this last paragraph and that’s because the theory requires more explanation than I can justify in this comment but if you want to find out more you should watch [this video](https://www.youtube.com/watch?v=F0b8b_ykPQk&ab_channel=PBSSpaceTime). If you want some more detail, consider [this lecture type video](https://www.youtube.com/watch?v=KYfFCApo-Rg&t=2284s&ab_channel=SeanCarroll). If you would prefer to read your info, you can look at the [IEP page for time](https://iep.utm.edu/time/) and browse the topics covered. If you want *even more* rigorous (but potentially difficult) info, check out the [SEP page on time](https://plato.stanford.edu/entries/time/).
Those encyclopedia pages will likely raise questions about time that you never knew you wanted an answer to.
The passing of events, and an event could be anything that can possibly happen, exist or be in the past, present or future.
Time does not exist. Time is made up by humans to help in daily life scheduling.
It is always “now”.
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