Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jman05 on 27/06/2005 17:31:05
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Im a big fan of stephen hawking and I just can't understand or get his theory of how you can slow down or bend time. Time to me is a man made measurement of motions or actions we take. Just a reference for us. Like i moved my hand up ** time ago. Its not like space that can be moved because space isnt made up by us. He also says that if you move faster than ligth you will age slower than people on earth. I read this secion of his book in detail and I just don't get it and think about it alot! Help me understand this concept.
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Time is not a man made measurement any more than is space. The unit of measurement (seconds, minutes, centuries, etc.) are man made, but time itself is not. Just like units of space measurement (millimeters, inches, furlongs, etc.) are man made units but space itself is not man made.
Also, in his book, he is not discussing going faster than light. He is discussing going some significant percentage of the speed of light without exceeding the speed of light. If a person could travel at 1/2 the speed of light (1.5 x 10^8 m/s) RELATIVE to the earth, their experience would not change, but their "time" would be slower than that on earth. So, if they traveled at that speed for a long period and then returned to the earth, they would not have aged as much as their colleagues that stayed on earth. They would have effectively "travelled to the future". As the relative speed increases, the dialation of time increases. But, according to current theories, there is no way to travel faster than light, and in fact, no way for matter to travel AT the speed of light.
This is no explanation of how this works. The best book I've seen on relativity is "Relativity - the Special and General Theory" by Albert Einstein. Yes, THE Albert Einstein. He was a very gifted communicator as well as physicist.
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John - The Eternal Pessimist.
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quote:
Originally posted by tweener
...The best book I've seen on relativity is "Relativity - the Special and General Theory" by Albert Einstein. Yes, THE Albert Einstein. He was a very gifted communicator as well as physicist.
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John - The Eternal Pessimist.
Tweener is right about the book. It is written at a high school math level, which makes it a great layman's book. Everybody should read this book. If you are looking for a challenge, read "The Meaning of Relativity", by A. Einstein.
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I still dont understand how you can have a different time if you were inside of this ship traveling faster than light. First off your just traveling really fast and I just dont see the relation to time. I will try to read einsteins book though.
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another way to put my misunderstanding is if the guy in the ship and the same guy on earth would move his hand 2 inches at the same speed, i dont get how the guy in the ships hand would get there before or after the guy on earth. Because time is just a measurement of his natural abilities to move.
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To each person, time doesn't slow down or speed up. Things still happen at normal pace for each person - then still walk around normally etc.
However, if the person on earth were to watch the person on the spaceship, then the person on the spaceship would appear to be in slow motion. The reason for this is that the speed of light has to be constant for both people. Now, in space there are no fixed points, so everything is relative. Each person can validly say that they are stationary without breaking any laws of physics. Therefore if the person on the spaceship measured the speed of light, he/she would get the same answer as the person on earth. However, relative to each other, the 2 people have a relative motion, as the spaceship passes the earth. Therefore, in order for the speed of light to be constant for 2 people travelling at different speeds, the rate at which time passes for each person must be different. This is why time dilation occurs.
"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
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I think jman05's confusion is that he separates time from space. That is Newtonian thinking. Time and space were unified by special relativity, and must be understood as a whole. In special relativity, spacetime is described by a metric known as the Minkowski World Coordinate System. (Minkowski was a mathematician Einstein had great respect for.) It has the coordinate vectors x,y,z,-ict. This replaces the Newtonian (A.K.A. Gallilean) x,y,z, at a universal t. From this coordinate system, and the constancy of c, special relativity can be understood.
P.S. A spaceship cannot travel faster than c. c is a limiting velocity for all mass-energy.
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Its still hard for me to understand.
But does this mean that peopple that live along the eqator hae slower time than people on the poles. I assume there is a huge difference in the speed they travel from earths rotation.
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The answer is yes, people who live on the equator live longer. But, the difference is negligible, as the speed difference is a minute fraction of the speed of light. Lets perform the calculation.
Diameter of earth: 13000km
circumference of Earth = 13 000 000 * pi = 40 830 000 m
Earth rotates once per day = once every 24 hours = 7.27 * 10^-5 radians/sec
=> tangential velocity = 472.72 m/s
The speed of light is 300 000 000 m/s, so the velocity due to the earth spinning is only 0.00016% of the speed of light, rendering it negligible!
"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
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The time dilation equation has a root-square function in the denominator, so it is less sensitive than a linear relationship. Here's a simple explanation of time dilation from a Caltech web site. I recommend you start with the Lorenzian length contraction, however, because the time dilation is derived from that.
http://www.theory.caltech.edu/people/patricia/srelb.html
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Wow. I've been reading this for like 2 days and I finally understand what you mean. But it seems odd that the natural law that light can only travel so fast will cause time to slow down so that it wont be broken. It seems like a cheap way for God to protect his laws(im say this in a jokingly way). Is it the actual speed of light law that is beign protected or is it just that nothing can travel faster than that speed and ligth happens to meet that speed so its not directly because of the speed of light. Like if we found something else that traveled the speed of light it woudlnt be directly because of it. If you get what im trying to say.
Also why doesnt the speed of light slow down by x amount instead of slowing down time?
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Oh wait. It cant be directly because of the speed of light because what if there are no lights on or if it is in dark space with no light on it. Time would still slow down wouldnt it?
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Time dilation doesn't rely on light but it does rely on the speed of light being constant. Whether there is light in the certain segment of space you are looking at is irrelevant - all we are saying is that if you performed the experiment of measuring the speed of light you would get the same result no matter how fast you were travelling.
Its like travelling in a car moving at constant speed - you can perform the measurement of how fast it is travelling (relative to the road) to show that its speed is constant, but irrespective of whether you do measure it or not, it will still be moving at a constant velocity (as that's how we defined it at the start).
So irrespective of whether there is any light in a cetain segment of space, the speed of light is still constant (as that is how scientists have defined is based on what they believe to be true).
Time dilation therefore does not rely on light, but relies on the fact that light always travels at the same speed in a vacuum.
"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
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Another way of thinking about it: Photons only, and only photons, move at the speed of light.
R A Beldin,
Improbable Statistician
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Can time be sped up or slowed down. Yes, I do it all the time, by saying I'm going to speed up time now, and low and behold the flight I'm on suddenly is over, 8 hours have past like five. Maybe it isn't time but our perception of it that can be changed. Who are we anyway really except a perception of that which we experience.
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The only way I know to slow down time is to switch on the television when George W. Bush is giving a speech. Sorry....
chris wiegard
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Einstein’s a joker
Me and the wife tried this slowing down time thing the other night ,but found the faster i went the quicker i came
And as for that length contraction rubbish
Its all balls if you ask me
Sadly there weren’t any observers so I couldn’t ask
their opinion.
But tonight I’ll turn my attention to Newton’s first law regarding internal forces and whether or not momentum is conserved
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I can't fault anything valibrarian or ukmicky have just said.
But I do disagree with the point made earlier by qpan that "people who live on the equator live longer". A clock on the equator actually runs more quickly than one at the poles, according to general relativity. The reasoning is as follows:
- the earth isn't perfectly spherical, it bulges out at the equator
- so the gravitational attraction at the equator is less than at the poles (the equator is further from the earth's centre of gravity, and gravitational strength varies inversely with distance-squared)
- gravitational force slows time down (according to GR), so relative time actually passes more quickly where the relative gravitational attraction is less (i.e. on the equator)
- this effect more than compensates for the opposing effects of SR (special relativity)
Of course, the overall effect on clock speeds would be very very very miniscule.
qpan would have been right (about time running slower at the equator) if the earth were a hollow shell - i.e. if if we didn't experience gravity.
P.S. Einstein himself originally made the prediction that a clock would run slower at the equator, in his 1905 paper on Special Relativity. It's a good job they didn't have the technology back then to be able to test this prediction - it would have been proved wrong, and people would have rejected SR. And who knows, maybe Einstein would then never have gone on to develop GR - he might have thrown in the towel and become a fishmonger. Or something.
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In the Heinline book "Stranger in a strange land" the witness answered the question of what color a house was with "It is white on this side". I.e. I will only state as fact, that which I personally know.
What do scientists really know about time slowing down? Will people age slower? Not known. What we know is that the probability of radio active decay is decreased with the attainment of sub-light velocities, and everything else has been an abstraction from that proven fact.
1) cosmic rays create particals in the upper atmosphere that shouldn't be able to reach the ground due to their rapid radioactive decay, but they do if they are traveling very fast. I.e. the probability of radioactive decay is decreased.
2) Cerium based atomic clocks loose time while in orbit around the earth traveling at relativily low velocities of 22,000 mph.
Will our spacemen live 2 seconds longer because they spent a month in space? Come on. We are postulating and assuming a lot. It sells books and it might be right, but lets be sure we know what we are talking about and where the assumptions come from.
David
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Sparky, that's a very good challenge, I like it.
But do you accept the experimental evidence for the other predictions of special relativity, e.g. that the apparent mass of electrons and protons increases as they are accelerated towards light speed in a particle accelerator? Or that when a particle and antiparticle annihilate each other the amount of energy generated matches the prediction of E=mc2?
My understanding is that IF Einstein's 2 postulates underpinning SR are valid, then the phenomenon of time dilation must follow as surely as the phenomena of mass increase or mass-energy equivalence. So if you accept the latter phenomena, you ought to accept the former.
Or do you believe the postulates may not be valid (so mass increase might one day have to be explained by an alternative theory)?
Or would you rather I just shut up so that we can all get back to reading ukmicky's accounts of his nocturnal "experiments"?
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Solvay_1927
Just in case David decided to take your advice I thought I had better Post an update on my experiments regarding internal forces and whether or not momentum is conserved.
And the answer was yes according to my wife the other night’s momentum was defiantly conserved.
She said not to worry though and if next time I wish to move her I should rely more on external forces.
Not quite sure what she means but I shall investigate further.
She also said Newton’s Postulations were not 100% right.
As she felt she gave more than me and that for every action there was defiantly not an equal and opposite reaction.
She then continued by saying that unfortunately Einstein’s theory that mass must increase with speed is defiantly wrong.
I can’t say I totally agree with my wife I see it being a bit like Einstein’s theory on special relativity you will always find there will be opinions that go contrary to what’s generally accepted.
Michael
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quote:
Originally posted by Solvay_1927
Sparky, that's a very good challenge, I like it.
Well, I guess I am saying that what has been shown to be correct is that the strong force that effects the radioactive decay of the nucelus is affected by sublight velocities. The question is are the other two forces also effected in such a way that we would interperte them as "time", or would our cerium clock simply run slower and loose time on our spaceship and we would continue to age at the same rate as on earth? I don't think the connection between our electrochemical aging and the strong force are all that clear.
In the past, many theories have been advanced that seemed logical and airtight. I guess I am just a natural doubter, and go around theories poking to see if there is any weakness. When people extrapolate a few facts to describe the entire universe of facts, I smile and think of how well the rasin pudding example explained the known facts of the atom back before Ruteford's experiments with x-rays.
I believe we can yet discover wonderful things about the universe. And the things that appear to be limits and barriers now, may someday fall away.
As far as particals increasing in mass, I don't know what experiments have been done on that theory. It basicly is one of the many barriers to sublight travel. (radiation from dust and even atomic collisions being another). There is still a lot of illogic in physics I am trying to wrap my brain around. Pull a neutron apart and out jumps an energy packet traveling at the speed of light (neutrino). That is like instant acceleration, good thing it is massless. Well, insanity beckons...
David
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It seems that Einstein didn't reject the idea of objects travelling faster than the speed of light as long as they never travel slower than light velocity. The idea of objects travelling slower than "c" and, never breaking this velocity limit would always have to move below this speed limit. Wouldn't such a concept of "travel faster" than "c" mean that objects could travel backwards in time?
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Within the theory of Special Relativity, yes it would. But there are always a few problems to keep life interesting. SR hates the idea that information can be exchanged faster than the speed of light. Some experiments with the wave nature of light seem to be challenging that concept.
As far as traveling faster than light, it is already been done. Light slows down when moving though other media than a vacumn. And partical accelerators have sent things faster than light travels though say water.
And why does light slow down in water, or oil or air do you ask. Naughty boy, don't ask questions we can't answer yet. Is there some interaction where the photon somehow reacts with the atoms (slows down, or time slows down) and yet is not scatttered apprecatively? Sorry, NO EXPLAINATION in SR.
David
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The best book I've seen on relativity is "Relativity - the Special and General Theory" by Albert Einstein. Yes, THE Albert Einstein. He was a very gifted communicator as well as physicist.
Is there an online resource where you can read this book and others.
Michael HAPPY NEW YEAR (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
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quote:
- so the gravitational attraction at the equator is less than at the poles (the equator is further from the earth's centre of gravity, and gravitational strength varies inversely with distance-squared)
- gravitational force slows time down (according to GR), so relative time actually passes more quickly where the relative gravitational attraction is less (i.e. on the equator)
Be careful you do not confuse gravitational attraction and gravitational potential. Gravitational attraction is the force (per unit mass) experienced by a small mass located at that point; graviational potential, however, is how much energy (per unit mass) is required to move the object from some previously defined reference point to that point. Thus, gravitational attraction is the gradient (differential) of potential.
The question therefore rises: Is the clock rate affected by the intensity of gravitational attraction, or the value of gravitational potential? I believe it is the latter, because and understanding of how gravity attracts, when examined at the quantum level, leads to the conclusion that it attracts because of a gradient in time. The gradient in the clock rate thus equates to a gradient in potential, meaning that the clock rate equates to potential. What that means is that any 2 points at the same altitude have the same clock rate, even if they do not have the same gravitational intensity. Assuming that the earth's surface is an equipotential surface (very nearly true of the oceans), the clock rate everywhere thereon must be the same -- not considering, of course, the effects of motion. Taking that into account complicates the picture in ways I do not understand.
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quote:
Originally posted by ukmicky
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The best book I've seen on relativity is "Relativity - the Special and General Theory" by Albert Einstein. Yes, THE Albert Einstein. He was a very gifted communicator as well as physicist.
Is there an online resource where you can read this book and others.
Michael HAPPY NEW YEAR (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
Certinly. http://www.gutenberg.org/etext/5001
[:p]
The mind is like a parachute. It works best when open. -- A. Einstein
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Cheers jimbob ,where were you 4 months ago.[:)]
Michael
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What part does Hawking's description of the origin of time as having "space-like" dimensions?
Doc
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well time is not man made as ur saying. If you think that time is what takes b/w the motion or activity then this means that if ur standing still or sitting still then there is no time. we are bound in the time and space.