Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: nilmot on 10/11/2004 08:38:53
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In last weeks assembly in our college the Physics teacher talked about Time and what really caught me was that he said Time is not set, it's different to everyone. So your time might be slower or faster than my time.
Time is said to be the 4th Dimension. The way he descibed it is that in order to descibe 3D, we can take a step back to look at the world in 2D and if you ask a 2D person to walk in one direction forever in this world. He will eventually come back to where he started (remember we are speaking theoretically here people, he will be dead by then). As for time, if you ask a 3D person to approach one dimension in a speed so fast that it will eventually get back to the same time. (Is this making any sense)
I'm not sure I quite understood it myself because I'm not really a Physic person as you can see i don't post a lot of message on this section of forum.
One interesting theory or experiment the scientists did was:
Have 2 clocks set exactly to the same time.
Tie one clock to a space shuttle and one stay on the ground.
Fly the shuttle round Earth as fast as is can go.
What they said was when the shuttle reach the same point as the stationary clock. The two clock will have different time, the one on the shuttle will go slower. Confusing or what...
Tom
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hi Tom
you're referring to Einstein's special theory of relativity (as opposed to his general theory) which desribes what happens to objects as they approach the speed of light.
If you fired a gun from the front of an aeroplane, how fast would the bullet be travelling ? The answer is the muzzle velocity of the bullet (which we'll assume is the same under all conditions), PLUS the speed of the aeroplane. So if the plane were doing 500 km/h and the bullet left the gun at 5000 km/h you would measure the bullet's speed as 5500 km/h.
But if you now shone a torch out of your aeroplane, how fast would the light measured by an observer appear to be travelling ? The answer is, at the speed of light of course ! It's a constant. But what about the motion of the plane ? Well, to correct for this paradox, time for the plane slows down so that the extra speed the light would have had due to the velocity of the plane is compensated for. This is referred to as time dilation.
The example you cite in relation to physically measuring this effect refers to the work of some physicists in the early 1970s who flew highly precise caseium clocks around the world on aeroplanes.
They were able to measure nano-second differences between the airbourne and earth-bound clocks. The clock on the aeroplane, relative to the clock on earth, was travelling much faster, and hence time slows down for that clock, relative to the one on earth.
It takes some getting your head around.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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One cool fact is that some astronauts are whole milliseconds behind us in time relatively [:D]
wOw the world spins?
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That's true, I'd not thought of that !
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Special relativity has a few basic tenents:
1. All observers in inertial reference frames get the same results when they solve for the laws of physics.
2. The speed of light in vacuo is a constant for all observers. It is also the limiting speed for mass/energy/information transfer.
3. Momentum is conserved.
From these tenents, we have a number of surprising results.
a. Distance is not conserved, it can contract.
b. Time is not conserved, it can dilate (slow down).
c. Mass is not conserved, it can increase.
d. Different observers in differing reference frames will not observe the same events at the same time. These results are the sometimes difficult problems posed to physics students in their intro to relativity course.
All this is easier to understand if you first understand the coordinate system Einstein used. It is called Minkowski's world coordinate system. The coordinates are x, y, z, and -ict, where i is the complex operator, and c is the speed of light. This is not the same as the Newtonian/Gallilean system of x, y, z, with t being identical for all observers. Most of the apparent paradoxes of relativity come from this pivotal difference in coordiantes.
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The question has been posed for years as to why time flows in only one direction.
and doesn't the fact that if light cannot escape a black hole say there is a force that moves faster then light? Otherwise how could it capture it.
I will always think that time is an observation of an ideal but ultimately isn't really there.
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It is good to be alive! It's impossible I'm here but here I am.. and I rock!
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Well, time is there, otherwise we would all have "no time". As to why it doesn't go backwards... according to Minkowski, that's the way it goes. The dimension is -ict. Time flows into the past at the speed of light. You know you can never take it back, whatever it was. That's because time is moving into the past at c. That postulate is also the source of all the Lorentz contraction and time dilation. Since time is already moving at c, and c is the limiting velocity, any additional velocities in x, y, or z, cause time to slow down. At x, y, or Z = c, time stops.
Of course this immediately begs the question as to why time can't be reversed, whatever reference direction we choose to start with. I suppose the answer is that would require faster-than-light travel.
Now black holes are a different story. In general relativity, gravity is not modeled as a force, as Newton did. There is no action at a distance. Gravity warps space, so that light is bent because traveling a straight line is a curve in the presence of mass. When the mass becomes large enough for the escape velocity to exceed c, that space is pinched-off, so light cannot escape the pinch, and it travels in circles inside the event horizon.
None of this squares with quantum mechanics, and that is the central problem in physics today. If you have a real answer for that, don't tell me. Send it to Physical Review, and collect your Nobel prize.
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No - a 'static' observer would see your time go slower the faster you travel, but your experience of the flow of time would not change.
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There is no "static", only relative velocities. Two observers traveling past each other, each observe the other's time dilation. A clock that they keep with them in their own inertial reference keeps their own reference time, and the moving clock they observe keeps a slower, dilated time.
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This is all getting a bit confusing for me..
Tom
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Thats why I put the static in single quotes!
Trying to relate special relativity to someone who only "see's" Euclidian space is never easy, small steps, gently taken.
I once had an A level physics teacher tell me electrical signals were instantaneous. It took HIM an age to 'get' it. I walked out of that night class shortly after.
But at O'level (Showing my age here) I had a brilliant teacher that sparked my curiosity, who would discuss relativity & quantum mechanics, teaching us slowly, using 'simple' stepping stones to help us understand the non-euclidian geometry, and the, at first, mind bending nature of both disiplines.
All extra curricula, he was brilliant. Sorry getting nostalgic, a good teacher fondly remembered.
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I keep seeing references to physics courses using letters; "A", and now "O". This seems to be a common method in the UK, but west of the Atlantic, I've never seen it. We do say "physics 101", when we are refering to a freshman level intro to Newtonian mechanics course. In my college, it was just "physics 01". However, even though the courses may increase in "number" as the curriculum advances through the subject matter(s), we would never say "In my 112 course I studied QM", instead we would just describe the course name as "Quantum Mechanics".
In the UK is there some formalism with the letters of the alphabet that is understood at the university level to indicate the course material?
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quote:
Originally posted by nilmot
This is all getting a bit confusing for me..
Tom
Tom.....please don't feel alone...I'm sure there are others here who are also just as confused as you. I'm not one of them of course !! It's clear from my postings on this site that I'm up there on Sandwalkers and Gsmollins level. Try and keep up Tom...tch tch tch[;)]
'Men are the same as women...just inside out !'
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O's and A's , now GCSE's (all pre-university).
O'level Exams - Secondary Education (High School).
A'Level Exams - Sixth Form and College (Sixth Form - an extra year (or two) at high school, College - the bit between School and University or career (Vocational/Technical colleges).
There are now also Sixth Form colleges, another tier of confussion, for schools that now don't have their own Sixth Forms, or pupils that don't want to study in the Sixth Form of their old school.
University - I think we agree on that.
Just to confuse the issue a lot of colleges are now called universities, but there are A list universities and B List, the A list being the old uni's ie Oxford, Cambridge, Essex, Anglia....
Don't get me wrong some of the old colleges (now uni's) are very good and should be in the A List, but over here we are still snobs, an Oxbridge Degree (Oxford/Cambridge) is still considered best.
The statements in the last two paragraphs are highly volatile and may explode in the hands of anybody who didn't gain a degree in an A list Uni :)
PS: I didn't!
PPS: Any views stated are mine, you may agree or disagree, its your choice!
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quote:
Originally posted by gsmollin
Well, time is there, otherwise we would all have "no time".
I did read the rest of your post Gs, not just singling out this quote blindly. :)
The black hole/light explaination was nice but even if light is trapped just inside the event-H you have light in an orbit out of sight? The "pull" or whatever would have to travel faster then light in that enviroment if no more then a nano-second or it would create energy we could see all the time. We only see this as gass, etc. slaps the horizon. This "Pinched off" is beyond the speed of light I guess.
Got to love black holes.. So far away they can't effect our local-verse of the Sun and planets; Yet, they distort our thoughts on reality like they do their local space/time.
Makes you wonder if consiousness is not restricted to time or space but just is, for it is effected by things far away that can't be seen.
As for time being a dimension, it seems more likely that it is not but more of a "function"(?) or relationship with space. Like light is a particle and a wave, space and time make up a single unit we just happen to see both parts of (like a spectrum?)
Time is like a hologram of everything in the past/present pulled to the point of you reading this. It describes how the universe exists at any single moment in space. Maybe it's just a visable system of distance and speed.
This makes more sense to me because you can remove time and the "system" don't change it just becomes viewable all at once.
Ok.. that's enough for me.. my mind requires good beer.
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It is good to be alive! It's impossible I'm here but here I am.. and I rock!
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It's possible that there is a super massive black hole at the centre of our galaxy.... so that has a direct effect on us, as the whole galaxy is formed by it. Plus gravity has an infinite reaching effect, travelling at the speed of light (most likely) your gravitational force is effecting everything around you.
wOw the world spins?
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quote:
Originally posted by Sandwalker
O's and A's , now GCSE's (all pre-university).
O'level Exams - Secondary Education (High School).
A'Level Exams - Sixth Form and College (Sixth Form - an extra year (or two) at high school, College - the bit between School and University or career (Vocational/Technical colleges).
There are now also Sixth Form colleges, another tier of confussion, for schools that now don't have their own Sixth Forms, or pupils that don't want to study in the Sixth Form of their old school.
University - I think we agree on that.
Just to confuse the issue a lot of colleges are now called universities, but there are A list universities and B List, the A list being the old uni's ie Oxford, Cambridge, Essex, Anglia....
Don't get me wrong some of the old colleges (now uni's) are very good and should be in the A List, but over here we are still snobs, an Oxbridge Degree (Oxford/Cambridge) is still considered best.
The statements in the last two paragraphs are highly volatile and may explode in the hands of anybody who didn't gain a degree in an A list Uni :)
PS: I didn't!
PPS: Any views stated are mine, you may agree or disagree, its your choice!
Huh? I think relativity is easier than the couse-naming convention for it!
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Radeon, is that your insight about the parallel orbits inside/outside the event horizon? If so, then you are pretty insightful. It was just this problem that led Stephen Hawkings to propose the quantum radiation from balck holes. Of course, the Rooskies were working on it too, but H had the better math, and he was able to explain away the thermodynamics problems with black holes at the same time. GR is a classical theory, and does not answer all the nitty-gritty questions, but it has been tested to great accuracy where it does apply.
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quote:
Originally posted by gsmollin
Radeon, is that your insight about the parallel orbits inside/outside the event horizon? If so, then you are pretty insightful. It was just this problem that led Stephen Hawkings to propose the quantum radiation from balck holes. Of course, the Rooskies were working on it too, but H had the better math, and he was able to explain away the thermodynamics problems with black holes at the same time. GR is a classical theory, and does not answer all the nitty-gritty questions, but it has been tested to great accuracy where it does apply.
When I come here I just dump thoughts down, so you are getting mostly the best of the crack in the crack-pot. [;)]
I failed College Algebra 101 three times so i don't read or follow anything published that has to do with mathmatics. It all should just add up right? not for me.
I generate questions and answers I can't prove to anyone lol!
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quote:
Originally posted by Ultima
It's possible that there is a super massive black hole at the centre of our galaxy.... so that has a direct effect on us, as the whole galaxy is formed by it. Plus gravity has an infinite reaching effect, travelling at the speed of light (most likely) your gravitational force is effecting everything around you.
I haven't studied gravity but it seems logical that it's a force that is instant. Like if you could create moon size gravity with some device and turned it on the effects would be to everything in space/time instantly not ripple out like an explosion.
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gsmollin
They are not relativity course naming conventions, there the English exam system, Scotland has something different, and Wales speaks another language. [:o)]
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Im curious about something.
If you had pointed a torch off the back of a plane, what would happen to that light as opposed to a torch being shown off the front of the plane.
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I tried to find a thread to put this in, i hope this is good
I'd like to know Why is time affected when we travel at the speed of light? how or why are they related?
Laith
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quote:
Originally posted by Laith
I tried to find a thread to put this in, i hope this is good
I'd like to know Why is time affected when we travel at the speed of light? how or why are they related?
Laith
If you want to avoid the maths (which, by the standards of some aspects of physics, is not the most complicated of maths), the basic issue that Einstein had to face was the increasing evidence that the speed of light remains constant to all observers. What this means is that, while light appears to travel at about 3 x 10^8 m/s, if we were to speed up to 2 x 10^8 m/s, light would still seem to be travelling at 3 x 10^8 m/s, and no matter how much we try and run faster, we never seem to get any closer to the speed of light (we may seem to be closer to the speed of light when looked at by someone else, but when we look at ourselves and our own view of the world around us, we still seem no closer to the speed of light).
What this means is that our view of speed (i.e. the speed of light) must be changed depending on our own speed (i.e. there is no absolute notion of speed, or absolute rest, since at whatever speed someone on the outside sees us, and however close to the speed of light they may think we are going, we cannot see that ourselves, but still believe the speed of light is as far away from our own speed as ever, and so the outside observer and us have different views of the speed of things – this is known in relativity circles as different reference frames).
Since speed is a measure of the amount of distance covered in a given amount of time, so it follows that if two different people can have a different perspective on speed, then they must either have a different perspective of distance, or a different perspective on time. What Einstein created was a set of equations that allowed that distance and time would change in a way that met the requirements that the speed of light seems to remain as far away as ever, not matter how fast you try to run.
What experimental evidence we have supports the accuracy of these equations as far as we can ascertain at this time – i.e. the way these equation indicate the universe should behave seems to match the way we perceive it to behave.
Incidentally, if you could not find a thread to add your question to, then why not consider starting your own thread (if you open up a forum – e.g. Physics, Astronomy, Cosmology – you will see a link at the top that says new topic, if you click this you can start a new thread).
George
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Thanks for the answer, I'm still gonna read it again so my brain can digest it better, it’s too late now, almost 5 am here.
Obviously I know how to start a new topic, you really didn't need to go in detail that much, ill try to look better through old threads next time, or start a new one.
Laith
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quote:
Originally posted by Laith
Obviously I know how to start a new topic, you really didn't need to go in detail that much, ill try to look better through old threads next time, or start a new one.
Sorry, didn't mean to patronise – I agree, I should have remembered that you have started enough topics of your own – but in my case, my brain was just in the process of still waking up (at least, that is my excuse).
George
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God, I just *love* this thread! It's given me a pleasant evening of reading and mulling over the theories. It's some time since the profoundness of the Special and the General Theories actually hit me. But when it did, it was one of those 'Kennedy' moments. You have to put aside all those preconceptions you've built up about matter and time and look at it from a completely new perspective.
Great stuff!
Roy P
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quote:
Originally posted by Sandwalker
Don't get me wrong some of the old colleges (now uni's) are very good and should be in the A List, but over here we are still snobs, an Oxbridge Degree (Oxford/Cambridge) is still considered best.
But Cambridge is, of course, the best of the bunch! [:D]
Brand new forum at
http://beaverlandforum.y4a.net
More than just science
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quote:
From these tenents, we have a number of surprising results.
a. Distance is not conserved, it can contract.
b. Time is not conserved, it can dilate (slow down).
There is also 1 more consequence that is very important: Distance and time can not only contract and dilate, they actually interconvert into one another, meaning that what to one observer appears to be a time interval between 2 events in the same place, will appear to another to be a time interval AND a difference in position; and likewise what to one observer is a distance separating 2 events which happen simultaneously, will to another appear to be a distance separating them, as well as a time interval between them.
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As to why it doesn't go backwards... according to Minkowski, that's the way it goes. The dimension is -ict. Time flows into the past at the speed of light.
In quantum mechanics, this is not so: time can move either directione equally well. The apparent irreversibility of time seems to have to do rather with the way we observe it, as affected by the Second Law of Thermodynamics.
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Of course this immediately begs the question as to why time can't be reversed, whatever reference direction we choose to start with. I suppose the answer is that would require faster-than-light travel.
Now black holes are a different story.
Well, as I understand relativistic gravity, time slows as altitude decreases. For a very large body it slows considerably as you approach the center in a quasi-stationary manner, and in the case of a black hole, stops entirely at the event horizon. However, the event horizon does not necessarily have a zero diameter, meaning that one can proceed further than that. That suggests that on the other side of it, time runs backwards; however to be sure of that conclusion we would have to examine the equations describing a black hole to see whether they are "well behaved" or singular at the event horizon, and I am not familiar with these.
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and doesn't the fact that if light cannot escape a black hole say there is a force that moves faster then light? Otherwise how could it capture it.
No; your sink drain which is percieved as at rest, is effective to capture water that is moving.
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Time is there because we put it there. It is there so that we can measure our activities in relation to day and night. It has been adapted over many years to be used in all areas of measurements but it is really a human invention to simplify our lifestyle. Time doesn't flow, it moves forward as a mechanism of our thoughts. We use it to measure but we should really be concentrating on distance and not time. We could still travel over distance if there was no light (hypothetically speaking of course) and even though we couldn't see we would still be going somewhere. Does this still involve time?
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Having worked my way (slowly, as befits my years)through this thread I find it seems to confirm a conclusion I came to some time ago. We are all moving through spacetime at the same speed - the speed of light. I am still wrestling with the problems that arise from that conclusion. [:-\]