Let's talk about time.

This might not come out all too clear, but for me, it was a novel way of thinking about time. It may very well be very wrong or unoriginal, but I never put it in this perspective before.

As a layman, I’ve often heard of space and time being the same thing, or at least, 2 sides of the same coin. I still always though of time as something that could be reckoned with directly. As an actual aspect of something tangible. Then, I began to strip the idea of time-as-tangible from what meager knowledge I have of physics. What if time didn’t exist. For real. Could time be a side effect of matter’s interaction with space (gravity?). Sort of like a shadow of a 3-dimensional object. We perceive the shadow, but it is nothing that can be directly interacted with, although it does seem very real to us, as if we could peel it off the ground if we didn’t know any better. I’m thinking time is nothing directly tangible as space is. Time is really only a perception humans have, only because our brains (physical as they are) are designed to process causality, being themselves subject to interacting within space.

I guess I thinking less of space and time as space-time, and more of time as a consequence of space and matter interacting through gravity’s lens.

Also, if the universe was nothing but empty space, could you say that time exists? What if you introduced one hydrogen atom?

Sorry if this isn’t very profound, I’ve had a couple beers. :stuck_out_tongue_winking_eye:

I seem to remember some discussion of time as nothing more than a measuring stick. You can measure an object’s length, width, and height with the first three dimensions and then time is the fourth dimension to measure the object’s progression through space. But physics makes my head hurt so I’m probably misremembering.

Which is true to our perceptions, but that measuring stick looks of different lengths depending on how fast it’s accelerating, or what gravity well it’s in (relative to us).

Maybe my OP is nothing more than rephrasing the obvious, but I wonder if there’s a distinction. Especially with the question:

Well, I guess my answer would be no. If nothing exists anywhere then time does not occur because it wouldn’t matter if something happened a year ago or a minute ago or a second ago because there is nothing to happen. Freaky to think about though.

IOW: I’m saying time is not another dimension (e.g. the fourth dimension). It’s merely a phenomenon borne by the presence of matter in space.

If there were completely empty space, could you really say it was three dimensional? What does fill our space is four dimensional, and one of those dimensions is time.

But, if space-time is one entity, then can space still ‘expand’, and if it can, is there still some sense of time? Or would the idea of space with no matter, provide no frame to measure space expanding?

Where’s a physicist when you need one?

Well, I don’t know. Why couldn’t empty space contain 3 dimensions? If we stripped the universe of all matter and energy as it stands now, would 3 dimensional space remain, and time seemingly vanish? If time stayed, what is being measured along that dimension? Or, if empty space has no dimensions, does that mean empty space would magically take on 3 dimensions and time as a fourth, if we introduce just one atom?

Or… or we can talk about McCain or Palin?

Time is running out in this regard.

Why would time cease to exist without the presence of matter, but the 3 space dimensions would endure, especially considering how intertwined space is with time?
What the hell does ‘endure’ mean without time?

I don’t understand how you can describe space as ‘tangible’. It seems your problem is that you stripped off time and said 'Gee, this can’t be real. I mean, what if there is nothing for time to measure, huh?" But what if there is nothing for space to measure? If time measures duration, but ceases to exist when there is nothing durable to measure, why doesn’t space cease to exist when it contains nothing long, deep or wide? How do you picture a totally empty space? Space with no fields, energy, matter, etc?

Anyway, I don’t see how you can justify your conclusion with regard to time, but not space. How do they differ? What is physics all about, then? What do physicists study, if time and space aren’t ‘real’?

You might try Googling the name Leonard S. Cutler, who was an atomic clock scientist and who was one of the leading lights in the field of frequency control. You might have to separate the wheat from the chaff as his name is shared by others but if you can find access to any of his papers and if you can understand them, you might gain a lot of knowledge regarding time and time keeping. I don’t mean the comment about understanding his work in any snarky way; it’s just that the man was brilliant in a very specialized field.

No, I know my thinking isn’t completely clear, and that’s due to my limited knowledge. So, could it be said that if we strip all matter and energy from space, then space wouldn’t really be there as a substrate, medium, whatever?

I might be diving more into philosophy here, rather than physics, but what is space without matter and energy? Or is that what space is, the culmination of these particles and fields?

So when the last star has radiated it’s last bit of energy, and the universe has run completely out of fuel, will that be the end of time?

These are great questions that no one can answer. My own thoughts are that space and time are attributes of matter and fields. That a piece of matter has a spatial extent in three independent directions, and one temporal duration, and that it is convenient to model space-time as a separate whole to ease the calculations. Sort of like how we talk of a field at a certain point that influences an object, instead of a huge amount of separate objects collectively imparting a force on that object.

Space without matter in this view is kind of undefined. Certainly many people would disagree with me. But if I define space or time as “the sum total of places it is possible for an object to be” or “All moments or instances when a particle can possibly exist”, then yes, when the last drop of matter and energy depart from the universe, space and time will cease to exist.

I’ll reiterate though that this is a personal opinion and I don’t think it is possible to defend with any kind of evidence or even reasoning. I just find this perspective useful.

How would you measure the passage of time in empty space? It’s kind of a “tree falling in the woods” thing.

Gravity is the interaction of space-time and matter. Specifically, matter causes space-time to bend kind of like bowling balls sitting on a mattress. Those curvitures cause nearby objects to accelerate towards each other, resulting in what we experience as gravity. Or another way of thinking about it is the closer you get to a mass, the curviture of space causes there to be fewer and fewer paths away from that object.

The classic example of extreme bending of space and time is a black hole. Nothing escapes from a black hole but not because it acts like a super-powerful irresistable vacuume cleaner or tornado-like vortex. The dense mass of a black hole bends space-time around it to such an extent that once you pass a certain boundary (the event horizon) the curviture is such that the number of paths goes to zero. Basically your bowling ball broke a hole through the damn mattress.

You’re all wrong. Time is a 4 corner simultaneous 4-day cube in only 24 hour rotation!

–FCOD

How would you measure the extent of space without the presence of matter? How long is three inches when there is nothing to measure and nothing to measure with? Another ‘tree falling’ thing, as well.

I don’t know a ton of physics, but according to an article I read in Discover magazine recently, some people are doing experiments at quantum levels, and if you bore down to a small enough scale, time basically ceases to exist. The guy in the article theorized that time may be like the surface of a swimming pool. It isn’t something that exists in its own sense, but rather is an aggregate effect of smaller interactions. I’m not sure how much I buy this, but its one more theory to consider.

forgive me if i get a bit mathematical here, but since the question of time as it relates to the universe is essentially one of mathematics, i see no other way of answering.

time, in the context of modern physics, is simply a dimension. it’s a parameter of the distance function that describes the metric space of spacetime.

in classical physics, distances were measured using a euclidean distance metric (d = sqrt(x^2 + y^2 + z^2)). now, in order to say two particles are such “distance” apart, one must integrate over the path that connects them in spacetime (the geodesic). time is a portion of that path, and so one also integrates across the time variable.

essentially, time is a mathematical construct (or part of a mathematical construct) that we use to accurately describe what we see in the world around us. there is nothing intrinsically important about it, just as there is nothing intrinsically important about the various dimensions of space. it’s just something we plug into equations that seem to best approximate how the world works.

as to whether or not time would “exist” if there were no interaction of matter in the universe (forgetting for a moment my misgivings about using “exist” as a predicate), this is similar to asking if the x and y dimensions exist on a piece of paper that has no graph drawn on it. to wit, it doesn’t matter one way or the other. it’s the wrong question to ask.