Yes, it does.
relativity and speed of light for dummies
- Thread starter mito
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Re: Time
I think it is very important to understand what time is, and isn't. Just as we are talking about movement in space along the x,y,z axis, when we are talking about time we are talking about relative movement. E.g. the movement of the earth around the sun, or the moon around the earth.
Time is very similar to money in that respect, in that it creates a relative value which you can use to measure something. This relative value can be concrete, for instance gold coins, but can also become totally abstract (virtual money). Time is similar - the concrete form are our clocks, which in all their forms have some form of physical, regular movement (hourglass, pendulum, wind-up, sun-dial, atom clock, etc.). All these concrete forms more or less accurately exhibit a regular, predictable form of movement which you can use to measure other movement.
All mistakes such as the concept of travelling back in time derive from losing track of the physical reality behind the abstract concept. In case of time, if you realise that time is relative movement, then it is a small step to realise that if you were to travel back in time, the universe would have to shift in reverse and move backwards retracing it steps exactly, while you remain the same. Totally and absolutely impossible. Conversely, if we can stop ourselves from moving while the rest of the universe moves on (say freezing ourselves), we can, in effect, travel to the future - you don't move, but everything else does. But, it is very much a one way ticket.
Re: Free Will
Whether free will exists depends on your definition. It's as easy or complicated as that. Our complicated neural network and organic body has all sorts of desires which come from itself (primitive urges, such as eating, sleeping, etc.) and from its interaction with the environment. I am my complex neural network, my identity consists of the routine in my brain that can observe and react to itself (consciousness), and when I react in a certain way to a certain situation (a choice of two actions or paths) I do so based on my primitive urges and earlier conditioning through previous interactions of urges and environment. But the key word here is that I do so, not something else. My will is the way I, as in my whole entity, urges and conditioning and all, react. My free will is limited only when an external circumstance prevents or causes me to act contrary to what I, as my own entity, want to react. This is not so much as when I want to grab an Apple, but someone stops me by restraining my hand - I still 'want' to grab the Apple. It is more like I am thinking about painting my house purple, but an external force monitoring my brain activity intervenes and modifies my brain so that I think about painting my house white instead. At that point I no longer have a 'Free Will'.
(hey, only 50% off-topic ... )
I think it is very important to understand what time is, and isn't. Just as we are talking about movement in space along the x,y,z axis, when we are talking about time we are talking about relative movement. E.g. the movement of the earth around the sun, or the moon around the earth.
Time is very similar to money in that respect, in that it creates a relative value which you can use to measure something. This relative value can be concrete, for instance gold coins, but can also become totally abstract (virtual money). Time is similar - the concrete form are our clocks, which in all their forms have some form of physical, regular movement (hourglass, pendulum, wind-up, sun-dial, atom clock, etc.). All these concrete forms more or less accurately exhibit a regular, predictable form of movement which you can use to measure other movement.
All mistakes such as the concept of travelling back in time derive from losing track of the physical reality behind the abstract concept. In case of time, if you realise that time is relative movement, then it is a small step to realise that if you were to travel back in time, the universe would have to shift in reverse and move backwards retracing it steps exactly, while you remain the same. Totally and absolutely impossible. Conversely, if we can stop ourselves from moving while the rest of the universe moves on (say freezing ourselves), we can, in effect, travel to the future - you don't move, but everything else does. But, it is very much a one way ticket.
Re: Free Will
Whether free will exists depends on your definition. It's as easy or complicated as that. Our complicated neural network and organic body has all sorts of desires which come from itself (primitive urges, such as eating, sleeping, etc.) and from its interaction with the environment. I am my complex neural network, my identity consists of the routine in my brain that can observe and react to itself (consciousness), and when I react in a certain way to a certain situation (a choice of two actions or paths) I do so based on my primitive urges and earlier conditioning through previous interactions of urges and environment. But the key word here is that I do so, not something else. My will is the way I, as in my whole entity, urges and conditioning and all, react. My free will is limited only when an external circumstance prevents or causes me to act contrary to what I, as my own entity, want to react. This is not so much as when I want to grab an Apple, but someone stops me by restraining my hand - I still 'want' to grab the Apple. It is more like I am thinking about painting my house purple, but an external force monitoring my brain activity intervenes and modifies my brain so that I think about painting my house white instead. At that point I no longer have a 'Free Will'.
(hey, only 50% off-topic ... )
You should read the original "The Time machine" by H.G. Wells, he has a wonderfully clear explanation, and it predates (1895) the theories of relativity.
Cheers
Time in *general* relativity is a very *local* construct. Its no different than length, in that sense. Its just a parameter that ticks. It does feel time dilation, so its perhaps better to say its a 'graded' local parameter (eg it depends on relative motion of observers).
As for its 'global' behaviour, in general relativity, all hell breaks loose. It depends on the metric (or the form spacetime assumes). For instance, just inside a vanilla blackhole's horizon, one of the units of length changes place with the time coordinate and becomes the only new sensible definition of time.
Its better to see it mathematically:
http://en.wikipedia.org/wiki/Schwarzschild_metric
Look at the form of the metric, and look at the second term: F(G,M,r) dr^2. Notice that if r < R, the second term becomes negative (and the first term becomes positive). The second term becomes timelike, and the first term lightlike.
It means that coordinates can change their physical meaning in global bodies. In some sense its just that the naive way of how humans like to think of what distance, or time means, are only crude approximations to a deeper mathematical entity (spacetime), and that indeed things can and will change around (drastically in this case). Point being, choice of coordinates is an entirely manmade construct in general relativity, there is no preffered or godgiven way to do it. This is sometimes called general diffeomorphism invariance.
From a theoretical and aesthetic standpoint, this is perhaps the single most beautiful result of 20th century physics.
As for its 'global' behaviour, in general relativity, all hell breaks loose. It depends on the metric (or the form spacetime assumes). For instance, just inside a vanilla blackhole's horizon, one of the units of length changes place with the time coordinate and becomes the only new sensible definition of time.
Its better to see it mathematically:
http://en.wikipedia.org/wiki/Schwarzschild_metric
Look at the form of the metric, and look at the second term: F(G,M,r) dr^2. Notice that if r < R, the second term becomes negative (and the first term becomes positive). The second term becomes timelike, and the first term lightlike.
It means that coordinates can change their physical meaning in global bodies. In some sense its just that the naive way of how humans like to think of what distance, or time means, are only crude approximations to a deeper mathematical entity (spacetime), and that indeed things can and will change around (drastically in this case). Point being, choice of coordinates is an entirely manmade construct in general relativity, there is no preffered or godgiven way to do it. This is sometimes called general diffeomorphism invariance.
From a theoretical and aesthetic standpoint, this is perhaps the single most beautiful result of 20th century physics.
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Another interpretation of time dilation is this invariant:
x^2+y^2+z^2+t^2=c^2
Where x,y,z is describing your velocity in space, c is the speed of ligth and t is your velocity in time. The above means when you're standing still, you're "falling" through time at the speed of light (and conversely when you're moving really fast in space, you're not).
Cheers
x^2+y^2+z^2+t^2=c^2
Where x,y,z is describing your velocity in space, c is the speed of ligth and t is your velocity in time. The above means when you're standing still, you're "falling" through time at the speed of light (and conversely when you're moving really fast in space, you're not).
Cheers
I'm having trouble understanding the "standing still" part. I take it it's not the usual term for "standing still", or it would be possible to send something in space and "make it stop" relative to our movement in space... Ok now i'm confused again.
Oh, of course there's nothing "standing still." It's relative. For example, if a rock and you have moving at the same (constant) speed, you can say the rock is "standing still" relative to you. So, the rock is moving at the speed of light at the time axis from your perspective. It may be quite different from other people's perspective.
I don't see why 'standing still' (or stopping you're motion in absolute terms) wouldn't be just as difficult as going the speed of light (in a vacuum). It would make sense that the two absolute ends of the spectrum of motion (be it through time or space) would be something equally "hard" to attain.
Glad the illustration helped. But but if you and I where on a runaway train nearing the speed of light and stuff started getting weird I'd grab you by the shirt collar and be saying something like "GOOD GOD MAN, WHAT THE ***K IS GOING ON HERE???!!". That's what I mean. I can't really understand it because I've never experienced anything...wait I take that back. Do a solid handful of shrooms and it helps a bit to understand it. I should have mentioned that part. Probably helped more than any physics class.
qft That's anyone who didn't get the implications of this should re-read until they do. If you didn't understand how a wing worked you'd be wondering how a plane stays in the air without flapping it's wings. It's easy to take for granted what time really is because our experience with it is very limited.
I'm not 100% sure what you are asking but I think the you are correct. Going lightspeed ain't so hard. Photons do it all day long. It's just that accellerating massive bodies (as in anything atom-sized and up) takes alot of effort. standing really still gets tricky because of relativity, which dicatates that you san sit there motionless and some jackass strolls by and suddenly you are moving, according to him. Thats not wordplay either, it's the truth. On top of that relativity shows us that space is expanding as well so there are you moving or not? And if somehow you can stand absolutly still you are still moving thru time. Before I go on, tell me if I'm on the right track here.
So nothing is "still", where the word "still" has a completely different meaning than our "still" but has something to do with being... still .......
Bigus Dickus
Regular
No, it doesn't, and physical experiments have proven that quite unambiguously.
Bigus Dickus
Regular
There is no absolute reference. Nothing is "still" unless it is defined in relation to something else. If you start out from wherever you are now and reach .5C, then shine a flashlight, you'd find that the photons traveled away from you in whatever direction you pointed at the speed of light (by definition). Everything would seem pretty normal to you, except that you would see a lot of other stuff flying by at .5C with what from your perspective looks like a lot of relativistic effects. Any experiment you do now would repeat itself identically if you were traveling at .5C. In fact, it is just as correct at that point to redefine yourself as stationary and assert that everything else is moving at .5C relative to you... that would be perfectly correct.
What gets really tricky is when you factor not just velocity induced time and distance dilation (special relativity) into the problem but acceleration as well (general relativity). After all, that's why if you head out at 1C and then return it is your clock that is lagging behind, not the one at the "stationary" point you left from and returned to. Which reference frame experiences acceleration is the differentiating factor.
What gets even more tricky, and where I lose all comprehension, is when people talk about the universe rotating. I remember some postulates on time travel that required a rotating uinverse to work. Rotating with respect to what!?!
I have no training in this field.. However, here is how I think of it:
*I AM NOT CLAIMING THIS IS ACCURATE IN ANY WAY*
Both time and space are relative measurements.
To measure space, you need to compare two states that are different in time.
To measure time, you need to compare two states that are different in space.
The change in space with respect to time is velocity. Eg; in one second, object A has moved 1 metre.
But in effect, you are actually measuring the same thing.
In my way of thinking,
when delta of space is infinite, delta of time is zero.
when delta of space is zero, delta of time is 1.
the limit of delta of space * delta of time as delta of space appraoches infinity is the speed of light, C.
So while you can keep applying energy to go faster, your measurement of time is changing too.
If I accelerate 10m/s/s for the first year, get to speed X. I keep accelerating at 10m/s/s for the second year, get to speed Y.
You need to factor in that relative to your starting point, that second 'year' may be considerably longer, you observe getting to speed X at 1.5 years, but observe getting to speed Y at 10 years (as an example). So in effect your perceived acceleration from the starting point is slowing down, because delta time is getting lower.
Thats as simple as I can think of it.
Feel free to tell me how wrong I am.
*I AM NOT CLAIMING THIS IS ACCURATE IN ANY WAY*
Both time and space are relative measurements.
To measure space, you need to compare two states that are different in time.
To measure time, you need to compare two states that are different in space.
The change in space with respect to time is velocity. Eg; in one second, object A has moved 1 metre.
But in effect, you are actually measuring the same thing.
In my way of thinking,
when delta of space is infinite, delta of time is zero.
when delta of space is zero, delta of time is 1.
the limit of delta of space * delta of time as delta of space appraoches infinity is the speed of light, C.
So while you can keep applying energy to go faster, your measurement of time is changing too.
If I accelerate 10m/s/s for the first year, get to speed X. I keep accelerating at 10m/s/s for the second year, get to speed Y.
You need to factor in that relative to your starting point, that second 'year' may be considerably longer, you observe getting to speed X at 1.5 years, but observe getting to speed Y at 10 years (as an example). So in effect your perceived acceleration from the starting point is slowing down, because delta time is getting lower.
Thats as simple as I can think of it.
Feel free to tell me how wrong I am.
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That doesn't matter: if their past and future paths are fixed, then so is everything that interacts with them. Like, us. The light reflects from your face in exactly this way, because you took all those choices in the past, etc.