((Take a note that when I give my definition of time, it's from a purely philosophical point of view, through logical thought progress. It's not supported by facts or science. Don't take this as a scientific write up. Science holds no answer to whether time, or something that explains the illusion of time exists, the existence or non-existence of time is a hypothesis.))
Now this is a topic I keep wrestling with myself, and while I'm not expecting any definitive answers, I think it's an interesting subject.
So, essentially, the big question of the day in astrophysics is whether time exists or not. Time, as we understand it, seems to not exist, and is merely an 'illusion'
I get it. Time is not what we think it is. That much is rather certain, but this is where the science hits the wall. The leading hypothesis appears to go something like this: The past, present and the future exist simultaneously. Furthermore there actually isn't such a thing as 'now' if you were to see your life outside a space and time continuum, you would see a sort of a worm, sliced in pieces that would be called 'moments' the past, present and future are equally real. At the start of the worm would be you as a baby, and at the end, you just before your death.
Now here is the issue I have with that. If this is the case, what exactly dictates the moment that we are experiencing presently. Technically speaking, if all the moments are equally real and constant, then all of the events must also be unchanging. Why are we experiencing the moments we are experiencing, in the order we are experiencing them? Logically thinking, it appears abstract that without there being anything to assert the order in which we experience things, we should still somehow experience them in a manner that makes sense.
So the answer to this? Laws of thermodynamics. Aha! Got me! Thermodynamics dictate that things happen in a certain sequence, energy moves, changes and acts in a certain way in a specific order through... Time... Yeah, you guessed it... But if 'time' doesn't exist, then nothing ever actually happens. The reality is static, every moment that has ever happened and will ever happen already exist. Therefore, the laws of thermodynamics become obsolete, since nothing is actually happening in this static universe composed of moments. Now, don't take my word for it, it's not like I'm a physics major or anything. I'm more of a philosopher, but think about it. If every moment already exists, then nothing can ever 'happen'
So what is time? I don't have the answer for you. The science behind the fact that it is not what we think it is is pretty solid. But just because it is not what we think it is does not mean it doesn't exist. Just because time is not how it feels it is, doesn't mean it isn't there. If time didn't exist in any manner or form, we wouldn't need the 'coordinates' of time to explain at which point in history 'something' happened. We could just give the spatial coordinates and voila, "That's when Julius Caesar died!" In essence, I feel there is a great semantic confusion in the time debate. Claiming it doesn't exist just because we don't know how it exists is like claiming gravity doesn't exist. I mean really, do we have any idea what gravity is? Where it comes from? How it works? This is as much as we can say for sure: "Gravity is the force that attracts a body towards the centre of the earth, or towards any other physical body having mass." Despite this, we know for a fact gravity exists.
So... Doesn't that sound a lot like saying. "Time is the indefinite continued progress of existence and events in the past, present, and future regarded as a whole."? We know for a fact that things 'happen' and that they happen in a sequence, all science depends on this. This, is what I call 'time.'
Some people say time doesn't exist because there is no 'now' we can universally define. But the same logic could be applied to space. There is no 'here' we can universally define, my 'here' is just as different to your 'here' as my 'now' is to your 'now'.
So, how would I define time? Essentially, it seems to me that time is much like space. Like we constantly travel through space, we simultaneously constantly travel through time. As a matter of fact, since space expands faster than light, we travel faster than light in space. (There is a great difference in travelling in space vs. Relative to space) If time is like space, then it would be follow that we are travelling 'faster than light' in time as well. So essentially, what this means is that we are unable to travel 'back' in space, as this would require us to travel faster than light 'relative to space' which is by all accounts impossible. Similarly, we can only travel forward in time, at varying speeds, because travelling back in time would once again require us to travel faster than light. Essentially, this dictates we can only be in one point of time at once, and we can only travel to one direction through time, we can travel to that direction faster or slower, but essentially, we can never return to a past point in time. It's a difficult concept to grasp, but it's one that makes sense to me.
Finally, I would conclude that if time acts like space, then we can only ever occupy one point in time at once, just like we can only ever occupy only one point in space at once. This space I am occupying now is my personal 'here' and it is as real as it gets. This time I am occupying is now and it too is as real as it gets. I am not somewhere else in space, and I am not somewhere else in time either. And if I can only occupy one point at a time, then I must not live in a static block universe, and I must conclude that in some form, in some fashion, time does indeed exist, just like space does.