Does time slow down?

bogwalrus

Can time actually physically slow down or is it the perception of time that is the thing that slows down.

Like with a black hole. Does the person approaching the black hole not notice time slowing down while on lookers from a distance will see yer man moving in slo motion. So when i ask the question can time "actually" slow down what would make it do so and is it possiblt to calculate the effects of such a thing.


The reason i ask is due to a hypothesis that if something made time slow down to a stop then the present, past and future would all exist at one point "in time" meaing that all the "multi dimensions" that exist in time could possibly exist at one point also meaning a kind of completeness to existence.

I believe the hypothesis was that the universe is expanding evenly and consistently and when it gradualy slows down then time will gradually slow down concluding in what i said above.

SOL

A better way of thinking about this is that the speed of light everywhere to everyone is constant. Now imagine looking at a train going at half the speed of light. There is a laser on the floor shining on a mirror on the ceiling. To the observer on the train (moving with the laser and mirror) they see the laser go straight up and down at the speed of light, but now consider an outrside observer. If the train is already moving with the laser at half c then the light cant go towards the ceiling at the speed of light, because it would have a speed of sqrt(.5^2 + 1^2). If you can imagine this it may be useful in understanding other time dilation effects...

ceejay

There was an interesting article in New Scientist recently about whether time is a fundamental property of the universe, or something we just perceive. The researchers came up with a time-free expression of quantum mechanics, and talk about how time emerges as a statistical feature of the universe, much like temperature is a statistical feature related to the kinetic energy of particles. Here's an excerpt:

According to Connes and Rovelli, the same applies to the universe at large. There are many more constituents to keep track of: not only do we have particles of matter to deal with, we also have space itself and therefore gravity. When we average over this vast microscopic arrangement, the macroscopic feature that emerges is not temperature, but time. "It is not reality that has a time flow, it is our very approximate knowledge of reality that has a time flow," says Rovelli. "Time is the effect of our ignorance."

The full article is available here if you're a subscriber.

Personally I like to think of time as a measure of change, i.e. you can only tell if time has passed if some aspect of the system has changed. Time "stops" when there is no change. I don't think we'd be able to perceive that, since that perception and understanding would require changes in the part of the system that is us.

The closest we can come to seeing time "stop" would be where we can observe time dilation effects as described above, or situations where photons are slowed down to a huge extent in certain crystals. However time for us as observers will continue to pass as normal relative to our own frame of reference.

Ciarán.

bogwalrus

SOL wrote: »

A better way of thinking about this is that the speed of light everywhere to everyone is constant. Now imagine looking at a train going at half the speed of light. There is a laser on the floor shining on a mirror on the ceiling. To the observer on the train (moving with the laser and mirror) they see the laser go straight up and down at the speed of light, but now consider an outrside observer. If the train is already moving with the laser at half c then the light cant go towards the ceiling at the speed of light, because it would have a speed of sqrt(.5^2 + 1^2). If you can imagine this it may be useful in understanding other time dilation effects...

it took me about 30mins but i got my head around it. thanks. So time is relative to the observer and i finally understand it=)


Im still thinking about time though. Can someone give me a scientific expanation of time? I know that a good way of thinking about time is through causality but it doesnt answer the deeper questions. I think its probably too deep a topic to be honest really. We could probably start going on about time being illusiary.

great unwashed

Think about the things we use to measure time - things like the revolution of the planet, the revolutions of your watch's hands and then things like crystals in digital watches.

Time = item, emit

Items we use to measure time are the planet and its revolutions or the movements of another body nearby - the sun (mercury revolves very slowly - once every time it orbits the sun or so i,e, 88 of our days, so can you imagine living there there night and day would last a year!)

The clock in your computer is also something which emits signals periodically as does the crystal in a digital watch thus it keeps 'time' just the same as a pendulum swinging...

Periodicity then is the real measure of time for us - something which happens regularly exactly like time in music - someone hitting a drum regularly say once every second or twice a second or more. Your computer deals in units of time a lot smaller! A processor which works at 400 megahertz means that the clock emits signals in the order of 400 million of those signals every second - that's fast. 2GHz is 5 times faster ... hard to imagine those tiny parts of seconds but they have names like 'jiffy' and I think 'google' too.

Einstein saw time as embedded in matter or as an aspect of matter and of stuff i.e. items emitting or items moving such as atoms themselves giving off signals intermittently or periodically... or like the planet moving relative to something else.

Lastly, because time is basically matter in motion which is basically energy, time has a 'direction'. Your computer's clock will very slowly emit itself into nothing or into something different and it will stop emitting so it will be different at the end of its life and irreversibly so. It will run down. The earth too will stop revolving eventually - it is apparently slowing down very slowly. The universe, sorry to break it to you, is gradually going into a state of disorder - entropy - the arrow of time.

But hopefully there will be another big bang and it will all begin again a second (?) time

great unwashed

So, if you can change the periodicity of something like a crystal emitting or a planet spinning then, yes, you can change the speed of time. That crystal or the clock speed of your computer will emit at a different cycle if you take your computer and throw it into outer space. Gravity ceases to affect it as much and it adopts a slower cycle with longer intervals. (after a week in space it will have counted less than your friend's computer on earth because it's now counting in slooow mootioon.

I believe such effects are seen in the watches and timepieces of people flying in fast planes because speed also slows time down for some reason.

The speed of light is the upper limit of something in motion that we know of - nothing can travel faster than it, according to Einstein - it's a natural wall or ceiling beyond which is only theory.

bogwalrus

thats a very informative and interesting perspective on time great unwashed. It makes me think that if the periodicity of fundamental matter can be altered (like lets say a photon) then maybe the sped of light can be changed and time be used as a tool?? that probably sound like waffle. What i am trying to say is if we altered the smallest of forces that effect the periodicity of time and thus give the speed of light its limit (maybe?) then maybe it would be possible to stop time or move forward in time or something along those lines.


thanks:)

great unwashed

Photons or light slows down in water etc. does it not? (the bent pencil) but it can't speed up beyond what speed we know it travels in a vacuum or the highest speed we know it to travel. Maybe this is a natural limit or at least a limit for our minds and techniques and the tools available to us in manipulating the planck measurements. Quantum physics (or the pop amount of it I know) is very philosophical when we talk like this. Philosophers dwell on questions about "how we know" anything. In the past they dealt with how we know God and how we know about reality. Physicists still deal with questions about reality today and sometimes questions are better than answers!

ceejay

great_unwashed, I think you are confusing rate of change for time. If one oscillation has a longer period than another oscillation, that doesn't mean that time is flowing slower for the longer oscillation - it's just taking more time as you the observer are measuring it.

Also, your description of throwing the PC into space and reduced gravity affecting its clock seems wrong to me. There would be time dilation effects due to its velocity which would make it slow down relative to us, but if anything I thing the reduced gravitational force might speed up the clock - not sure exactly about how gravity/accelleration affects time in Einstein's general relativity theory.

Light does appear to slow down as it goes through matter, but this is more to do with the amount of interaction that takes place between light and the matter - it is still travelling at the speed of light inbetween each interaction with matter. Interesting reading about Cherenkov Radiation that talks a bit about this and about "faster than light" waves. Check it out on Wikipedia.

Ciarán

ga2re2t

Here's an interesting thought for you:
All photons move at the speed of light. Even if they've been "slowed down" or "accelerated" in another medium, they're still going at the speed of light in their frame of reference. But the equations of time dilation tell us that time stops at the speed of light. So in a photon's frame of reference, it is born and dies at the same time!

Think of this another way. For a photon which is created at the sun and is then absorbed by your eye's retina, no time has passed. This means, as far as the photon is concerned, its interaction with your retina could have influenced its creation at the sun!

Lovely stuff!

great unwashed

ceejay wrote: »

great_unwashed, I think you are confusing rate of change for time. If one oscillation has a longer period than another oscillation, that doesn't mean that time is flowing slower for the longer oscillation - it's just taking more time as you the observer are measuring it.

Well I don't think I am but I am open to correction. Rate of change IS Time - a measurement of something changing within an already agreed time framework, is it not? If two people are chopping down trees, one with an axe and the other with a chainsaw and they spend the whole day doing that then you'd say the one with the chainsaw will chop down more than the other in one day. Divide the day up into hours and you'll still say the second fella cuts down more trees in that unit of time, an hour.

If the fella with the hatchet is living on a planet like Mercury where a 'day' lasts 120 of our days and an hour there lasts two or three of our days or something then the man with the axe could possibly chop down as many trees as his chainsaw buddy back on earth in an hour relative to each.

For us, one unit of time measurement is the 'day' and we can measure work done and energy lost and expended during that unit of time or during a fraction of it because energy used is meaningful.

Similarly with a crystal or radiating substance if the oscillation is regular. Regular in terms of what though? Time is relative so we have to establish a framework.

Also, your description of throwing the PC into space and reduced gravity affecting its clock seems wrong to me. There would be time dilation effects due to its velocity which would make it slow down relative to us, but if anything I thing the reduced gravitational force might speed up the clock - not sure exactly about how gravity/accelleration affects time in Einstein's general relativity theory.

Gravity slowing Time I may have got this backwards but Gravity affects those oscillations we're talking about above - or is supposed to. Your computer's clock oscillates at a certain rate on the surface of the earth but if you take the exact same pc clock and leave it in space for a period of time then the oscillations of the crystal will be out of step with its brother on the earth. I think you've got it right - gravity slows the clock down on earth relative to the other. Someone asked this already on Yahoo and have included a wiki link on Gravitation.

Light does appear to slow down as it goes through matter, but this is more to do with the amount of interaction that takes place between light and the matter - it is still travelling at the speed of light inbetween each interaction with matter. Interesting reading about Cherenkov Radiation that talks a bit about this and about "faster than light" waves. Check it out on Wikipedia.

Ciarán

I should read more about light waves in other media - I'm lost at this point!!

ceejay

great unwashed wrote: »

Well I don't think I am but I am open to correction. Rate of change IS Time - a measurement of something changing within an already agreed time framework, is it not?

I would agree up to a point that change is necessary to perceive time passing, but I would disagree that time = rate of change. Rates of change measure how quickly something changes, and the figure is expressed as how much change there is per unit of time. This does not mean that it defines what time is. Your assertion would be analogous to stating that speed = time, since speed is the rate of change of position with time, but I think you would probably agree that speed is not time. I think though that what you are getting at is more about how we perceive and measure time passing, which is indeed relevant to the question of "does time slow down".

great unwashed wrote: »

If two people are chopping down trees, one with an axe and the other with a chainsaw and they spend the whole day doing that then you'd say the one with the chainsaw will chop down more than the other in one day. Divide the day up into hours and you'll still say the second fella cuts down more trees in that unit of time, an hour.

I can't argue with that, but it's still the same amount of time passing for each of them (assuming no significant relative velocity between them). There's a different rate of work, i.e. number of trees chopped down per day/hour/second/whatever, but the same amount of time.

great unwashed wrote: »

If the fella with the hatchet is living on a planet like Mercury where a 'day' lasts 120 of our days and an hour there lasts two or three of our days or something then the man with the axe could possibly chop down as many trees as his chainsaw buddy back on earth in an hour relative to each.

For us, one unit of time measurement is the 'day' and we can measure work done and energy lost and expended during that unit of time or during a fraction of it because energy used is meaningful.

Now here's where you start going wrong in my opinion. An hour or a day is not relative. An hour is not defined as one 24th of the planet's rotation, and therefore dependant on which planet you're on. It's 60 * 60 = 3,600 seconds, and a second is actually defined like this (from wikipedia):

International second
Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.[1] This definition refers to a caesium atom at rest at a temperature of 0 K (absolute zero). The ground state is defined at zero magnetic field. The second thus defined is equivalent to the ephemeris second, which was based on astronomical measurements. (See History below.)

So to talk about the amount of work done in an hour "relative to each" isn't really correct, and would be comparing apples and oranges. The amount of work they do in 3,600 seconds would be independant of whether they were on Earth or Mercury - assuming one of them could actually chop down trees on Mercury

great unwashed wrote: »

Similarly with a crystal or radiating substance if the oscillation is regular. Regular in terms of what though? Time is relative so we have to establish a framework.

The regularity here is relative to the passage of time in the frame of reference you're referring to. If you, the observer, are observing the period of oscillation of the crystal, and the crystal is at rest relative to you, then you are both essentially in the same frame of reference, and the oscillation will have a certain period.

If you or the crystal then move off at a relative velocity, then time dilation will come into effect, and the period of oscillation measured by you and the period of oscillation "measured" by the crystal will be different. This has been shown by taking highly accurate atomic clocks and sending one up in a plane and flying at speed for a while, and when comparing the time passed recorded by each clock, the one on the plane has recorded less time passing than the one that remained at rest - verifying Einstein's time dilation predictions from relativity.

The thing is though that if you were on the plane, your perception of a second passing would not change, and it would not feel different to a second passing if you remained with the clock at rest. It's only when you come back to a shared frame of reference that the time dilation effect becomes apparent. If you remained travelling at speed you would have no way of directly measuring the time passing at the clock at rest, other than doing the calculations based on the relative velocities. Your perception of when things happen would differ from the perception of an observer at rest, but until you matched velocities and joined their frame of reference and shared observations, you wouldn't be able to tell this.

So, to go back to your point, time is relative, but relative in that time passes differently in frames of reference in motion relative to each other, as measured in each other's frames of reference. However, within any given frame of reference, a second still lasts a second. This is what Einstein determined when he asserted that every observer measures the speed of light (in a vacuum) as the same, no matter what their relative velocity. If I'm travelling close to the speed of light and I shine a laser ahead of me, the photons speed away from me at 3 x 10^8 m/s. The point is, the phrase "I'm travelling close to the speed of light" implies that I'm travelling at that speed relative to some other frame of reference. As far as I'm concerned, if I'm travelling at a constant velocity, I might as well be at rest, and there's no experiment I could do to show that I wasn't at rest - assuming no accellerations. And this is where your next point comes in

great unwashed wrote: »

Gravity slowing Time I may have got this backwards but Gravity affects those oscillations we're talking about above - or is supposed to. Your computer's clock oscillates at a certain rate on the surface of the earth but if you take the exact same pc clock and leave it in space for a period of time then the oscillations of the crystal will be out of step with its brother on the earth. I think you've got it right - gravity slows the clock down on earth relative to the other. Someone asked this already on Yahoo and have included a wiki link on Gravitation.

This is moving into the realms of general relativity, where Einstein talked about accellerating frames of reference - and the force of gravity can be treated in this way. I have a poor understanding of general relativity, and only a somewhat better one of special relativity, but essentially there are time dilation effects due to accelleration also - which can include changes in direction as well as speed, so a rotating body is an accellerating frame of reference. According to Einstein rotating bodies actually drag spacetime around them to some extent, though I couldn't tell you what that actually means in terms of time dilation or other effects.

great unwashed wrote: »

I should read more about light waves in other media - I'm lost at this point!!

Time dilation, relativity (special & general), time's arrow, etc., are all pretty head wrecking - and that's before you throw in the wierdness of the quantum world!

Ciarán.

great unwashed

ceejay wrote: »

Now here's where you start going wrong in my opinion. An hour or a day is not relative. An hour is not defined as one 24th of the planet's rotation, and therefore dependant on which planet you're on. It's 60 * 60 = 3,600 seconds, and a second is actually defined like this (from wikipedia):

So to talk about the amount of work done in an hour "relative to each" isn't really correct, and would be comparing apples and oranges. The amount of work they do in 3,600 seconds would be independant of whether they were on Earth or Mercury - assuming one of them could actually chop down trees on Mercury

Time dilation, relativity (special & general), time's arrow, etc., are all pretty head wrecking - and that's before you throw in the wierdness of the quantum world!

Ciarán.

You would agree that our friends on Mercury and Earth exist in two very different frames of reference with regard to Gravity which is what I think we're missing from the discussion. As you say, your head gets wrecked enough by thinking about half this stuff without throwing other stuff in on top of it but here goes. The Caesium International measurement of the second is unfortunately the earth second because I believe it assumes the 'ground state' is under the influence of earth gravity. Mercury's gravity might be a bit different. Perhaps the oscillations are only a couple of hundred or even a couple of thousand out (up or down) but I do believe that Einstein meant that gravity affects time in exactly this way.

Black hole lore says it does so that's where I'm coming from with the earthling and mercurian lumberjacks. Not really applicable to lumberjacking as you say but when the Russians sent a probe to Venus in the seventies they miscalculated the gravity or assumed it was like earth's - probably because Venus is of similar size (and mass?) but the probe slammed onto the surface as though it were ten times heavier. Venus doesn't rotate so maybe our planet counteracts the force of gravity in some way (this is my own fanciful belief).

Have you read into the General Theory of Relativity much?

ceejay

great unwashed wrote: »

You would agree that our friends on Mercury and Earth exist in two very different frames of reference with regard to Gravity which is what I think we're missing from the discussion. As you say, your head gets wrecked enough by thinking about half this stuff without throwing other stuff in on top of it but here goes. The Caesium International measurement of the second is unfortunately the earth second because I believe it assumes the 'ground state' is under the influence of earth gravity. Mercury's gravity might be a bit different. Perhaps the oscillations are only a couple of hundred or even a couple of thousand out (up or down) but I do believe that Einstein meant that gravity affects time in exactly this way.

Black hole lore says it does so that's where I'm coming from with the earthling and mercurian lumberjacks. Not really applicable to lumberjacking as you say but when the Russians sent a probe to Venus in the seventies they miscalculated the gravity or assumed it was like earth's - probably because Venus is of similar size (and mass?) but the probe slammed onto the surface as though it were ten times heavier. Venus doesn't rotate so maybe our planet counteracts the force of gravity in some way (this is my own fanciful belief).

I agree that the two lumberjacks represent different frames of reference, and not just due to the different gravitational forces they're experiencing - there's also the relative velocity between the two planets to consider, and this is not constant either due to the fact that the direction of motion is also changing all the time. So, there are definitely time dilation effects coming into play here. However, these effects relate to how each lumberjack measures the passage of time for themselves and relative to each other, meaning that they will not have the same perception of "when" events occur. This situation is exactly analagous to the classic example of the light being shone in a train passing a station.

But my overall point is that time dilation and other relativistic effects are not really what the original question was about - though it is an entertaining discussion nevertheless The original question was asking whether time can slow down in your own frame of reference, and is there a scientific explanation of what time actually is. I feel that even if you could slow time down in your own frame of reference, you wouldn't be able to tell.

The problem with discussing time is that generally we tend to mean the passage of time rather than the dimension of time. It's like using speed instead of position. The concept of time "slowing down" doesn't make sense if you're talking about the dimension of time, in the same way that the concept of position slowing down doesn't make sense. But then we don't seem to be able to control where we are in the dimension of time in the same way we seem to be able to control where we are in the dimensions of space - we're always moving from one moment to the next - time's arrow.

great unwashed wrote: »

Have you read into the General Theory of Relativity much?

No, I haven't read that much specifically on General Relativity. I've read several pop science books, and always had a love of physics in school and college, so I have a degree of understanding of things like relativity and quantum mechanics. It can wreck your head though, trying to get around some of the concepts.

Ciarán.

bogwalrus

really enjoying your discussion on time lads. though im using every ounce of brain power to try and comprehend what you are talking about (since i have very little knowledge on relativity and not great at maths


I think the last thing you said there ceejay about the dimension of time is what i am on about. And what you say about not noticing if time (in the dimensional sense) was indeed slowing down is something i was thinking alright. I beleive there could be some relation between the rate of expansion of the universe and the perception of time in the universe. Why i think this i dunno but there is something that makes sense about it.
We all live through our sensory organs that give us the illusion of time so to get on with our analysis of the physical world. The fact that our eyes see what they see is only because we have not developed (evolved) the need to see farther than what is there.

Is sight the only thing that can truly determine time in the universe? As in we perceive time through our eyes. can our ears or nose tel the difference?he he, sorry for the weird question but it just popped into my head. An interesting one i hope. (probably not though)

Anyway time for me will always be an interesting one, probably because i dont understand it like you guys do but it just has so much significance into the why we are here questions and so on.

ceejay

I think from the biological point of view there are lots of systems in the body that are periodic, and thus we have an innate sense of time independant of being able to see. There are natural rhythms in the body - just think of your heartbeat, or the daily pattern of sleep and wakefulness.

I think I remember reading someone suggesting that our perception of time is related to moving from one thought to another, and as that rate changes our perception of how much time is passing changes. I think it's an inverse relationship, i.e. more thoughts per second makes it feel like time around us is slowing down. From Einstein himself:

When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute and it's longer than any hour. That's relativity.

Ciarán.

bogwalrus

that is so very true. never thought of things like that before. kind of like where the phrase time flys when your having fun spwans from.