Time is not a consequence of human perception. Everything in the universe is moving at the speed of light through space-time. Any object which is not moving through space, relative to some inertial reference frame, is moving at 100% of the speed of light through the time dimension, i.e., one second per second in that frame of reference.
don’t have much time right now, but interesting posts everyone, thank you.
I just wanted to say, I understand, or at least have a good grip on current relativity and quantum interpretations on space-time, and I want to be able to reply to some of the recent posts… Be back later tonight!
Time and space and force are all different faces of the same coin.
Matter and energy and information are all different faces of the same other coin.
Causality is a deeper concept than time, space, force, matter, and energy. The idea is that there can be causes and effects.
Time is nothing but the agency that ranks causes before effects. It appears to be “something” because we think about it with our brains, and brains are evolved to manipulate cause to create effect. It’s all they do. So it is a suitable mechanism to think about time.
At least, that’s what I think, as a physicist who does very little work with these concepts but likes reading Scientific American.
Right, see I understand that matter bends space-time in such a way, that what appears to be a curved path moving within the gravity field, is actually “straight” to the object moving through it.
I’m not ignoring general relativity, but just really trying to get to the bottom of how I should think about space-time. They’re obviously related, like electricity and magnetism.
We know how gravity works, but we don’t know why and what it is (yet). Is the same true for space-time? That’s the angle I’m coming at here.
Yupp, I’d like to have a discussion along these lines, but I don’t want it to devolve into unsupported musings. I see it’s mostly a philosophical hair-splitting I’m getting at here, but hey, I like discussing and reading about it.
In my thinking now, I’m just wondering if space can exist without matter or energy/fields. Or is it a by-product of matter and energy in some way? Is space-time it’s own entity, or does its existence depend on matter/energy?
That’s part of why I’m so confused. I don’t want to get into semantics and I’d like to stay true to preconceived definitions, but if you take matter out of space, what have you? Does it all become meaningless?
If you had a universe that had just one atom in it, would space still expand like our universe is? Would space (the universe) be sequestered to a tiny realm around it?
This gets closer to the heart of my thinking. The universe is a complex set of forces and rules. They interact with each other like a giant piece of software for, say, a game. Time, as we have evolved to perceive it, is nothing more than the consequence of physical causality. There is really no time, just space that harbors all this matter and energy. We perceive the rules of the game as time in this (admittedly, imperfect) analogy.
How certain are we about this? Mathematics, while important to our understanding of the universe, is still a model (albeit a damn good one). Mathematics can describe how, but never the why or what. So, I suppose I’m diving into philosophy here. I might be over my head.
Right, this is how I came to understand SR & GR. I read somewhere (probably here) that this is still, yet, an analogy to help us get a sense of how it all works. It’s a great way to visualize what’s going on at the surface, but is it an oversimplification? And while very cool and fascinating, not quite what I’m trying to get at here.
Thanks all, again, for indulging me,
-kev
One more thought, going back to my game-as-universe analogy.
If you think of the universe as a board game. In the past, I’ve always thought of matter and energy being played out on a giant board we call space-time; the fundamental forces were the rules of the game. Not so much now. Now I’m thinking matter and energy is the arena itself; the physical board and pawns, not space-time. Space-time would be the rules of the game.
Gah! My brain-lobes are throbbing.
Something else you might want to consider: the transition of a spatial dimension to a temporal one.
Regularly, we have three spatial and one temporal dimension. But at the event horizon (EH) of a black hole, the radial dimension changes from space-like to time-like. When you’re outside the EH, the world-lines of objects are “free” except for the time dimension. Everything advances in that direction.
Inside the EH, the radial direction becomes time-like. Everything must fall toward the center of the black hole. So we effectively have two spatial and two temporal directions. The world lines are free in the spatial dimensions (the polar and azimuthal angles) but must advance in the two temporal dimensions (down and our usual time).
An interesting extension of this, is that what we consider the time may simply be the radial direction of a universal black hole in a higher dimensional space that we are all “falling” into. I don’t think the evidence supports this, though.
Time requires an observer. It is relative to the experience and observation of an observer. No people ,no time. Like the old tree falling in the woods.
An observer is not a conscious mind. If the entire universe is at the (estimated) steady state of 3 Kelvin, there will still be time.
Isn’t that tantamount to saying, had sentience never evolved, then the universe couldn’t exist. I’m finding that hard to swallow.
I’m in the camp that believes the tree still makes a damn sound, whether anyone was around or not.
There is something to be said to require an observer to be aware to even ask these questions (basically, the universe has become aware of itself), but I believe a universe can exist, devoid of life.
Can a universe exist devoid of matter and energy? What is space or time without it?
If you had to sum up all of physics with two axioms, you could probably narrow it down to:
- Energy is conserved
- Entropy always increases
While you may be able to get by (1) without time, (2) necessitates a passage of time, and in fact defines the direction of time.
I think one step toward truly understanding time would be a theory of quantum gravity. Quantum mechanics has been successfully linked with special relativity, but not yet with general relativity. GR not only does funny things with time but fundamentally depends on it, and it would be enlightening if we could quantify it at a quantum level.
as to how certain we are: i have a relatively loose understanding of the math involved with general relativity and quantum mechanics, but i have a fairly solid understanding of why the math is the way it is, and why simpler maths (such as euclidean geometry) didn’t work.
it is absolutely a philosophical question, though. all of science asks “what is?” in an attempt to predict “what will be?” this is, in my experience, simply how we live our lives as humans. we all have a sort of intuitive understanding of the universe around us, which we use every moment to try and predict how our actions will change it. the theories newton derived did this more powerfully than anything before and perhaps anything since. but we found out that we could do better in certain situations (e.g. for objects moving near the speed of light relative to other objects).
at that point, we move away from the intuitive, i think, and simply go with what works. we can’t picture the world behaving the way our models dictate it will, because our models go against our intuition, and, after all, they are only, as you say, models. but they are the best tools we have for answering “what will be?” and so, we must admit that there is no necessary correspondence to “what is?” on a fundamental level, but we must also conclude that so long as our models adequately predict what will be, we should continue to use them.
in short: it isn’t science’s goal to determine the fundamental nature of the universe, but to predict how our interactions with it will change it. the models we currently use are the best we’ve come up with, and there’s no reason to believe or even desire that they are adequate representations of the fundamental nature of the universe.
I believe that a lot of confusion about this issue stems from a somewhat unclear definition of dimension, aggravated by a lot of popular science fiction depicting a ‘fifth dimension’ as a place one can go to, or from where saucer men can attack.
I think it’s best to think of a physical dimension as merely a measurement; thus, talking about time in empty ‘space’ is as nonsensical as talking about its temperature, or its greenness or whatever else attribute. In other words, time is just as real as space, it just depends a bit on what your definition of ‘is’ is. 
As to why time seems so different from other dimensions to us, well, it’s simply that our universe isn’t symmetric with respect to time, and we’re (if at rest in the spatial dimensions) also moving through it at the speed of light: we can remember the past, and anticipate the future, but not the other way around. Think of a three dimensional shape that’s symmetric in two of its dimensions: it’s got a distinct front and back. That, grossly simplified, is the case for all four-dimensional objects with respect to time. In this analogy, we’d further be moving through the asymmetric dimension, giving ‘time’ not only direction (which comes from the asymmetry), but also sequence: the object seems to evolve according to its asymmetric shape.
Though, I have to stress this again, this is only a (hopefully helpful) analogy, but the gist of it is that time seems distinct from space only because 1) the universe is (macroscopically) asymmetric in time and 2) all matter moves through space-time at light speed, and the majority of that movement (all of it if at rest in space) occurs through time.