dj357 wrote:Ok, thanks hackenslash for those posts, but here's my problem: All of that sounds like bollox. I mean, I'm sure the maths makes sense, but if we talk about time as NOT being a dimension and is simply the occurrence of events at the atomic and sub-atomic levels, then the quoted post about travelling through different dimensions etc... makes little sense. Maybe I'm just an idiot or I don't get it, but to me it seems remarkably convoluted to wrap up time as another dimension, which doesn't even make any sense (and I'm talking about in the middle-world Newtonian physics kind of way) as opposed to actually looking at what time really is.
Well, here's the thing. In General Relativity, time is a dimension. GR treats it as something very much like a spatial dimension, through which we are travelling at the maximum velocity at all times. When we're moving through the spatial dimensions, that maximum is reduced, as explained above.
I've heard all sorts of definitions of what time actually is, but none has ever come close to GR as a means of dealing with what we actually observe. The caesium clock experiment demonstrates that GR is definitely on the right track in its conception of what time is and, to my knowledge, no other model has come remotely close. Further, you may think it's convoluted, but it is easily the simplest model that matches observations. We don't actually have any other model of time that works. Now, of course, we don't have anything like a complete picture, but treating time as a dimension makes things work, not least our GPS systems, which rely on a relativistic model of spacetime to maintain accuracy, and it does it to a remarkable degree of accuracy at that. In short, while we still have questions, it works.
Every other definition of time I've ever come across has suffered from the same problems, namely being perfectly pithy to the point of tautology while having absolutely no bloody utility whatsoever.
I do understand that there has been innumerable amounts of work done with spacetime as a solidifed concept and it works with the maths, but I'm trying to step outside of the maths for a second, as silly as that sounds. To me it seems as if making time an extra dimension is a way to justify the fact that we experience time as movement, in our heads at least. If I stop and think about exactly what time is, take a slice of time as infinitely thin as possible, to me, the reason why any speeds could be taken as zero for moving objects etcetera is because there are no atomic or subatomic events taking place.
Well, there are all sorts of problems with this. The first is that time as a dimension provides testable predictions that give repeatable results to a high degree of accuracy. The second is that it is far from clear that time can be divided in the way that you suggest. The smallest slice of time that we have been able to use is the Planck time, and this is really only a way for us to make it calculable. In reality, it's quite probable that time is a continuum, with no smallest unit. Think of it in terms of the biological concept of species (BSC). In fact, that's a really good way of looking at it, since the BSC requires a moment in time for definition. The fact is that there is no boundary between one species and the next, only a gradient of gradual change. This is why people have real trouble with the concept of species. The same is true of time and, indeed, space. What is the smallest unit of space? Is there one?
If you take an accelerating body and look at the difference in speed between 1 quadrillionth of a nanosecond and the next, given a low speed and low acceleration, you would see no change in the speed, precisely because there are no interactions happening on the subatomic or atomic level.
I think you're off in red herring territory there. In reality, given a high resolution, you would be able to measure change. You might not be able to perceive it with your middle-world senses, but you would certainly be able to measure, right down to the Planck measurements of both scale and time (except, of course, that the smallest time we have been able to directly measure is around 10
26). Bear in mind that the Planck time is a whole hell of a lot smaller than a quadrillionth of a nanosecond, at 10
-43 seconds.
If you take a human, and stop all atomic and subatomic interactions occurring within his/her body and in the space surrounding him, time would cease to exist for that person. Not because they would be dead or "frozen in time" but because within particle interactions, nothing happens. And, to us, in middle world, time is the occurrence of events. Does any of this make sense...?
That's because of the definition of time you're operating under, which isn't correct or even useful in any real sense. Time is not a measure of change, as some would suggest. This has value in high-school physics, but high-school physics is a long way from accurate. In the real world, this definition of time has no utility. You can make no predictions based on this definition of time.
Another related question, is the slightly slower rate of time experienced by a GPS satellite compared to an earth-bound clock, due to the gravity itself accelerating the satellite towards the centre of the gravity field or is it due to the angular motion of the satellite in the field...?
You've got that arse about face. A GPS satellite experiences two kinds of relativistic effect. The first is that it experiences time faster due to being further away from the Earth's centre of mass than an Earth-bound equivalent. The second is that it experiences time slower due to its velocity. The relativistic correction systems in GPS satellites take both of these effects into account.
So, to sum up:
1. Time runs slower for an observer immersed in a gravitational field.
2. Time runs slower for an observer in motion.
Both of these are predictions that stem naturally from the picture of time we get from General Relativity, namely as a dimension somewhat akin to a spatial dimension through which we are travelling at lightspeed while at rest in the spatial dimensions. Of course, the fact is that we
never experience time at its full rate, because our inertial frame is in motion, so we don't travel through time at lightspeed, but at lightspeed minus the relativistic reduction due to the motion of our inertial frame.
Edit: Bloody superscript tags!
