A hobby of mine is reading physics books. Mostly about Einsteins theory of SR in which he explained time dilation by using a car and train. A train is moving along a track at 100mph. Next to the track is a road with a car that is travelling at 50mph parallel to the train. If the driver in the car measures the speed of the train, he will record the train doing 50mph relative to him. An observer on a hill monitoring the whole show however, sees the train at 100mph....not 50 as the driver states. (logical) He also measures the car going at 50mph.
[][][][][][][][][][][][ train 100mph
>>>>>>>>>>> car 50mph
oooooooooooo outside observer
Now we replace the train with a light beam. The light beam (slowed to 100mph top speed for this example) is constant. The car, riding next to the light beam, is doing 50mph as in the example above. When the driver measures the speed of the light beam, he expects to read 50mph, but instead reads 100mph. The outside observer sees the beam at 100mph and the car at 50mph.
Now....the observer, using a telescope, looks into the car that is doing 50mph and sees the driver moving in slow motion. I understand everything except the slow motion part. The internet articles say he is in slow motion but to me, the driver, at 50% the speed of light (c) should be motionless. What do you think? I also understand length contraction of moving bodies, but thats not what I'm confused on.
Bettina
SR...
Why is this in Ethics and Commentary?
Bettina, I did a project on Special Relativity when I was a few years younger than you are now.
The simple answer is that the driver sees himself as going 50mph relative to the ground and he sees the light as going 100mph relative to him.
So the driver sees the light as going 150mph relative to the ground, and the observer sees the light as going 100mph relative to the ground.
Pick a distance that the light travels relative to the ground... say 300 miles. The driver sees the light travel that 300 miles in 2 hours. The observer on the ground sees it travel that 300 miles in 3 hours.
So 2 hours for the guy in the car is 3 hours for the observer.
If the driver picks his nose and it takes 4 seconds, it appears to the observer that it takes 6 seconds.
Hence the guy in the car appears to be moving in slow motion.
Bettina, I did a project on Special Relativity when I was a few years younger than you are now.
The simple answer is that the driver sees himself as going 50mph relative to the ground and he sees the light as going 100mph relative to him.
So the driver sees the light as going 150mph relative to the ground, and the observer sees the light as going 100mph relative to the ground.
Pick a distance that the light travels relative to the ground... say 300 miles. The driver sees the light travel that 300 miles in 2 hours. The observer on the ground sees it travel that 300 miles in 3 hours.
So 2 hours for the guy in the car is 3 hours for the observer.
If the driver picks his nose and it takes 4 seconds, it appears to the observer that it takes 6 seconds.
Hence the guy in the car appears to be moving in slow motion.
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I disliked physics all through school and used that class to do other homework. I got a passing grade because I could memorize what I needed to know but since I got interested in Einstein, I can't get enough of it now. I bought a ton of books too. One I'm reading now is "The fabric of the Cosmos" by Brian Greene.....Suncho wrote:Why is this in Ethics and Commentary?
Bettina, I did a project on Special Relativity when I was a few years younger than you are now.
The simple answer is that the driver sees himself as going 50mph relative to the ground and he sees the light as going 100mph relative to him.
So the driver sees the light as going 150mph relative to the ground, and the observer sees the light as going 100mph relative to the ground.
Pick a distance that the light travels relative to the ground... say 300 miles. The driver sees the light travel that 300 miles in 2 hours. The observer on the ground sees it travel that 300 miles in 3 hours.
So 2 hours for the guy in the car is 3 hours for the observer.
If the driver picks his nose and it takes 4 seconds, it appears to the observer that it takes 6 seconds.
Hence the guy in the car appears to be moving in slow motion.
Anyway, "So the driver sees the light as going 150mph relative to the ground" How can he? I thought light wasn't additive with other motions.
Light travels at 670MMPH, so if a car is doing 50 and he turns on his headlights, the light is not doing 670MMPH + 50...
Bettina
Light is always traveling at the same speed relative to the observer.
So if the observer is in a car and he sees light coming out of his headlights, he sees the light traveling at 670M MPH relative to *HIM* and he sees the ground traveling at -50 MPH relative to *HIM*. He therefore also sees the light traveling at 670M MPH + 50 MPH relative to *THE GROUND*.
Hope this helps. =)
So if the observer is in a car and he sees light coming out of his headlights, he sees the light traveling at 670M MPH relative to *HIM* and he sees the ground traveling at -50 MPH relative to *HIM*. He therefore also sees the light traveling at 670M MPH + 50 MPH relative to *THE GROUND*.
Hope this helps. =)
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That's the very thing that doesn't make sense. Why should the speed of light be the same, no matter in what reference frame the observer is? Note that I'm not trying to argue anything; I know some of the specifics of the theory. That's just the initial reaction I had to it, and every time I work with it, I always come back to the same thought: "Damn, this is bizarre!"Suncho wrote:It does make total sense. Everything else follows from the speed of light being constant.
General relativity on the other hand... Someone might understand it but I don't. =)
As for general relativity, I haven't quite made it there yet, but I have heard that Einstein single-handedly pushed physics ahead by decades with that one. It's likely that others would have developed general relativity within several years, but that one was his and his alone.
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Yeah. I guess I don't think of things as bizarre anymore. The whole concept of light is pretty abstract to me in the first place, so I guess I'm not bothered by it very much. =)Top Gun wrote:That's the very thing that doesn't make sense. Why should the speed of light be the same, no matter in what reference frame the observer is? Note that I'm not trying to argue anything; I know some of the specifics of the theory. That's just the initial reaction I had to it, and every time I work with it, I always come back to the same thought: "Damn, this is bizarre!"Suncho wrote:It does make total sense. Everything else follows from the speed of light being constant.
General relativity on the other hand... Someone might understand it but I don't. =)
As for general relativity, I haven't quite made it there yet, but I have heard that Einstein single-handedly pushed physics ahead by decades with that one. It's likely that others would have developed general relativity within several years, but that one was his and his alone.
Yes it's hard to imagine but I'm really facinated with this. I would give ten years of my life just to have lived next door to Einstein. I would be over there every day as his maid. He was cute too 
When you are standing still in your room, you are not moving thru space, but you are moving thru time. One second you were standing there, the next second your still standing there, and on and on. All of your motion is thru time. When you start walking, you are moving both thru space and time. You walked from one room to the next, from one second to the next. But, according to Einstein, you can't add them together. You divert some of your motion thru time to motion thru space. Time for you runs slower than it was when you were at rest.
So, motion thru space, and motion thru time must always equal the speed of light...no faster. Einstein simply stated that it was not magical and has to be accepted because its simply the way our universe works. Light is the top speed of our universe.
In 1971, they proved this fact by putting two atomic clocks in a plane and flew it around the world. When it landed, the two clocks were slower than two identical clocks on the ground by the exact amount Einstein predicted.
Suncho is already there so its not surprising to him. I am playing catch-up so its very exiting to me and thanks Suncho, I got what you meant now.
God, I love it.
Bettina.
When you are standing still in your room, you are not moving thru space, but you are moving thru time. One second you were standing there, the next second your still standing there, and on and on. All of your motion is thru time. When you start walking, you are moving both thru space and time. You walked from one room to the next, from one second to the next. But, according to Einstein, you can't add them together. You divert some of your motion thru time to motion thru space. Time for you runs slower than it was when you were at rest.
So, motion thru space, and motion thru time must always equal the speed of light...no faster. Einstein simply stated that it was not magical and has to be accepted because its simply the way our universe works. Light is the top speed of our universe.
In 1971, they proved this fact by putting two atomic clocks in a plane and flew it around the world. When it landed, the two clocks were slower than two identical clocks on the ground by the exact amount Einstein predicted.
Suncho is already there so its not surprising to him. I am playing catch-up so its very exiting to me and thanks Suncho, I got what you meant now.
God, I love it.
Bettina.
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Yeah. But from within your frame of reference, you are only moving through time and you see the dude in the car moving through both space and time.Topher wrote:Except you're still moving along with the earth's rotation with the earth's orbit around the sun with the sun's orbit around the galaxy...
From his frame of reference, he is only moving through time and he sees you moving through both space and time.
From within your frame of reference, the sun and the galaxy are moving through time and space and you're stationary.
Bettina, how are you at math?
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Not yet, but I have it here along with Eugene Savovs "Theory of Interaction". I finished another book by Michio Kaku called "Hyperspace".. It was great but not as good as this one.Suncho wrote:Bettina, have you read Brian Greene's "The Elegant Universe"? It's supposed to be more comprehensive than The Fabric of the Cosmos.
I wish you hadn't got me thinking about this stuff again. I gotta get back to work. =)
Topher.... If you liked "Brief history of time" like I did, Then "Fabric of the Cosmos" will end up being your all time favorite science book. Its over 500 pages and small print. A big read but you will love it. Promise.
Bettina
One more thing about Einstein. He was in his 20's while he was puzzled about spacetime and it came together suddenly while he was riding home on a streetcar. He had to sit in the rear because the front seats were full.
The seat was backwards so you had to look out the rear. As he gazed outwards and as the streetcar began to move forward, he saw the clock tower at the end of the street. Watching the large hands, he thought what would happen if the streetcar went away at the speed of light, and while he stared at it....it hit him...time would stop. He visited his friend the next day and told him he solved the problem.
I can't think of anyone I would love to be with at that point in time.
Bettina
The seat was backwards so you had to look out the rear. As he gazed outwards and as the streetcar began to move forward, he saw the clock tower at the end of the street. Watching the large hands, he thought what would happen if the streetcar went away at the speed of light, and while he stared at it....it hit him...time would stop. He visited his friend the next day and told him he solved the problem.
I can't think of anyone I would love to be with at that point in time.
Bettina
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Kilarin
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You can dismiss the rotation because it's affects are small, but you can't actually dismiss it the way you could if you were in a spaceship traveling in a straight line at a constant velocity. Rotation puts you in an "accelerated" frame of reference. It changes things.Bettina wrote:Yep, you can dismiss the earths rotation etc for your frame of ref.
For example, say you were on a big hunk of rock drifting towards alpha centauri. Several light years out so that the effects of gravity are very close to zero. You could say that you were approaching alpha centauri at .5c. OR you could say that you are sitting still and alpha centauri is approaching you at .5c. Other then measuring against the microwave background radiation, there is NO WAY to determine which view is correct. There is no "preferred" frame of reference.
Now lets move that back to you in your front yard on earth. You could say that the earth is spinning around on it's axis, OR you could say that the entire universe is spinning around the earth (As people used to believe). But this time you can prove which is right. Set up a Foucault's pendulum and you can prove that the earth is rotating. So here we DO have a prefered frame of reference.
Of course, the effects are so small that you CAN ignore them, but I find it interesting that they aren't so small they can't be detected.
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The short answer is yes... If you are motionless with respect to the ground, like standing still, all of your motion is thru time which is the speed of light.Pandora wrote:Question: is it always the case that an object's speed through time and space is the speed of light? Meaning that when an object is completely still it will move through time with the speed of light? Is this interpretation correct?
Its more complicated than that though, and I will find a link that better explains it.
Bettina
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Thanks, Bettina! Through your an Suncho's posts I am finally starting to understanding the theory. It has eluded me for about 15 years now.Bet51987 wrote:The short answer is yes... If you are motionless with respect to the ground, like standing still, all of your motion is thru time which is the speed of light.
That would be awesome. I googled a bit myself but couldn't find anything that explained it well.Its more complicated than that though, and I will find a link that better explains it.
The Speed of Light. If I remember correctly, the theory holds that this is the limit - nothing travels faster than light. Yet if this is correct then we have a BIG problem. If NOTHING travels faster than light, then the effect of gravity is also limited to this speed, which would create an attraction lag between the sun and its planets (it takes light a few minutes to reach earth and a few hours to reach the outer planets). Because of this slippage, after enough time the planets would slip away from orbit. To prevent this, the attraction of gravity must be almost instantaneous. Observation of distant galaxies supports this quality of gravity, where the entire disks of spiral galaxies are seen to revolve like a record - everything at the same speed no matter how far from the hub. Since gravity is a physical property in this universe, a force that can be measured, it is either propagated by waves or via gravtons (theroretical gravity particles), then this seems to indicate that the speed of light is NOT the upper limit, and that there is more to the universe than most people realize.
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I think it's more accurate to say that if an object is still relative to you with respect to the three spacial dimensions, that object is moving through time at the speed of light. That same object is moving through time at a rate slower than the speed of light when viewed by an observer that is moving spacially relative to that object.Pandora wrote:Thanks, Bettina! Through your an Suncho's posts I am finally starting to understanding the theory. It has eluded me for about 15 years now.Bet51987 wrote:The short answer is yes... If you are motionless with respect to the ground, like standing still, all of your motion is thru time which is the speed of light.
So if you see a ball sitting in front of you, from your perspective that ball is moving through time at the speed of light.
If a guy drives by in a car, he sees the same ball, but to him, the ball is moving through time slightly slower.
It's kind of sad; being a physics major, I feel that I should be able to expound on some of these points in more detail, but I find myself not being able to. I can barely remember half of what we did last semester. I really need to read \"A Brief History of Time\" nad some of those other titles one of these days...
I really need to read \"A Brief History of Time\" nad some of those other titles one of these days...Re:
Thanks!Suncho wrote:I think it's more accurate to say that if an object is still relative to you with respect to the three spacial dimensions, that object is moving through time at the speed of light. That same object is moving through time at a rate slower than the speed of light when viewed by an observer that is moving spacially relative to that object.
What still puzzles me is how the theory deals with situation in which it is ambiguous with regard to who is moving and who is still. Imagine two persons in deep space without any other frame of refernce flying past each other. For each of them it is as if they are moving and the other one is standing still (or vice versa, actually). In this situation, who has the faster speed through time and who through space?
Although it might be a stretch, the same question can also be posed for the example with the airplane and the atomic clocks. One might say (A) that the plane is moving faster then any place on the earth's surface. However, (B) from the plane's reference frame one would say that the plane is standing still, and the earth spins faster underneath it. As the experiment has shown, (A) is true. But why? How is something like this resolved?
Apologies, if this is a stupid question, but I really can't wrap my head around this one.
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If you're guy A, you're stationary and you're moving faster through time than guy B. If you're guy B, you're stationary and since guy A is moving, he's going slower through time.Pandora wrote:Thanks!Suncho wrote:I think it's more accurate to say that if an object is still relative to you with respect to the three spacial dimensions, that object is moving through time at the speed of light. That same object is moving through time at a rate slower than the speed of light when viewed by an observer that is moving spacially relative to that object.
What still puzzles me is how the theory deals with situation in which it is ambiguous with regard to who is moving and who is still. Imagine two persons in deep space without any other frame of refernce flying past each other. For each of them it is as if they are moving and the other one is standing still (or vice versa, actually). In this situation, who has the faster speed through time and who through space?
So the answer is that the moving guy is always going slower through time than the stationary guy. Which guy is stationary depends on your frame of reference. =)
B is also true. But forget about the spinning. Assume the earth is flat like a map. If you start factoring in spinning, acceleration, or gravity, we enter the realm of general relativity.Pandora wrote:Although it might be a stretch, the same question can also be posed for the example with the airplane and the atomic clocks. One might say (A) that the plane is moving faster then any place on the earth's surface. However, (B) from the plane's reference frame one would say that the plane is standing still, and the earth spins faster underneath it. As the experiment has shown, (A) is true. But why? How is something like this resolved?
Don't worry about it. There are some questions that special relativity just doesn't answer. In special relativity, if the other guy is moving relative to you, the other guy's time is always slowed down relative to your time.Pandora wrote:Apologies, if this is a stupid question, but I really can't wrap my head around this one.
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Although the speed of light is constant and is the upper limit, some scientists theorize that gravity exceeds C. Since this is not testable yet, we will have to wait and see, but for now, special relativity is universally accepted by the physics community and the experiments that appear to contradict it are due to errors in the experiments. All this could change in my lifetime if something is discovered.Shoku wrote:The Speed of Light. If I remember correctly, the theory holds that this is the limit - nothing travels faster than light. Yet if this is correct then we have a BIG problem. If NOTHING travels faster than light, then the effect of gravity is also limited to this speed, which would create an attraction lag between the sun and its planets (it takes light a few minutes to reach earth and a few hours to reach the outer planets). Because of this slippage, after enough time the planets would slip away from orbit. To prevent this, the attraction of gravity must be almost instantaneous. Observation of distant galaxies supports this quality of gravity, where the entire disks of spiral galaxies are seen to revolve like a record - everything at the same speed no matter how far from the hub. Since gravity is a physical property in this universe, a force that can be measured, it is either propagated by waves or via gravtons (theroretical gravity particles), then this seems to indicate that the speed of light is NOT the upper limit, and that there is more to the universe than most people realize.
However, the spiral disk phenomenon you mentioned is due to dark matter which in itself could have gravitational properties.
And Suncho.....I forgot to mention that math is my worst subject. I have good grades, but struggle with it.
Bettina
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Good. You're not learning anything if you're not struggling. Math is the perfectly logical order of nature. Math is the purest mind stretch. No one can be expected to keep it all in mind at once, but what's important is that we keep trying.Bet51987 wrote: And Suncho.....I forgot to mention that math is my worst subject. I have good grades, but struggle with it.
Bettina
The tricky thing with math is context. While you're in the process of solving a problem, you often don't know where you'll end up. That's why it's important to understand where you came from and never to lose track of where you are.
I guess what I'm saying is, try not skip anything hoping to pick it up later. You'll get stuck. Math is built on other math.
In high school, I was an alternate on my state's math team and I had no idea what the heck was going on. They thought I was smart so they basically begged me to join the team. But instead of doing the work, I played Descent 3. =)
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FYI; Mathmatics is from the ancient Greek word mathmatikos, which literally means "the business of learning." The word mathetes (pronounced mahth-ay-tays) is a derivative that means "student" or "learner." The ancient Greeks felt that all knowledge was derived via the science of numbers; all knowledge begins with mathmatikos.Bet51987 wrote: I forgot to mention that math is my worst subject. I have good grades, but struggle with it.
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Kilarin
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Biology is really just Chemistry
Chemistry is really just Physics
And Physics is completely dependant upon Math.
Math is just about the only science that stands on it's own. It's the heart and soul of ALL science.
And I HATED it when I was in school. I didn't discover a love of math until later in life when I played with it for fun.
If you want to read a book that will get you EXCITED about math (and many other subjects) try Gödel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter. Absolutely AMAZING book.
I also recommend Innumeracy by Paulos and Fermat's Enigma by Singh
Or for some immediate fun, if you aren't already familiar with them, read up on:
Cantor's Diagonal argument (Still sends goosebumps up and down my spine)
or visit Hotel Infinity (it's like having your brains smashed out by a slice of lemon wrapped round a large gold brick)
I WISH I had properly appreciated math when I was in school. It's the cats pajamas!
Chemistry is really just Physics
And Physics is completely dependant upon Math.
Math is just about the only science that stands on it's own. It's the heart and soul of ALL science.
And I HATED it when I was in school. I didn't discover a love of math until later in life when I played with it for fun.
If you want to read a book that will get you EXCITED about math (and many other subjects) try Gödel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter. Absolutely AMAZING book.
I also recommend Innumeracy by Paulos and Fermat's Enigma by Singh
Or for some immediate fun, if you aren't already familiar with them, read up on:
Cantor's Diagonal argument (Still sends goosebumps up and down my spine)
or visit Hotel Infinity (it's like having your brains smashed out by a slice of lemon wrapped round a large gold brick)
I WISH I had properly appreciated math when I was in school. It's the cats pajamas!
Math is an absolute relationship between quantities. Math exists independently of any kind of physical reality. Science involves measuring phenomena and forming theories. Math is absolute. Math can be used to describe a science, but it is not a science in and of itself. No matter what ideas we use to describe the way the world works, the number 1 is always the number 1. That can never change.
Nice Greek definition, Shoku. I never knew that. =)
Nice Greek definition, Shoku. I never knew that. =)
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Lothar
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Re:
I believe the theory says no OBJECTS (ie, things with mass/energy) travel faster than light.Shoku wrote:The Speed of Light. If I remember correctly, the theory holds that this is the limit - nothing travels faster than light.
Forces are not objects. Gravitational force is instantaneous. One way to think of it is that it's a warping of the fabric of space-time. When an object is in a particular position, it has already warped that fabric. If the object moves, the whole gravity field moves at the same speed. It's not like the gravity closest to the object moves, and then the farther gravity moves -- the whole field moves together.
Or, possibly, neither model is correct.Since gravity is a physical property in this universe, a force that can be measured, it is either propagated by waves or via gravtons...
P.S. Cafe topic.
Ooooh, Bettina is discovering the marvels of physics ...
How about some practical application?
There was a true story of a man caught passing a red traffic light. In trial he told the judge that he had been travelling so fast that the red light had appeared green to him. The judge knew a thing or two about physics, so he made a little calculation and fined the guy for speeding: He would have needed to cruise at one third of the speed of light to achieve that effect ... hrch hrch hrch ...
How about some practical application?
There was a true story of a man caught passing a red traffic light. In trial he told the judge that he had been travelling so fast that the red light had appeared green to him. The judge knew a thing or two about physics, so he made a little calculation and fined the guy for speeding: He would have needed to cruise at one third of the speed of light to achieve that effect ... hrch hrch hrch ...
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Cheers, Suncho. Did I get you right: and at the same time, my time is slowed relative to him, because I am also moving with respect to his frame of reference?Suncho wrote: In special relativity, if the other guy is moving relative to you, the other guy's time is always slowed down relative to your time.
(That is so weird...)
So they BOTH see eachother as moving SLOW? this confuses me... if (relative to eachother) the plane clocks are to Loose time and the ground clocks are to Gain time - then shouldn't the Ground clocks see the plane clocks moving SLOWER, and the plane clocks see the ground clocks moving FASTER?Suncho wrote:If you're guy A, you're stationary and you're moving faster through time than guy B. If you're guy B, you're stationary and since guy A is moving, he's going slower through time.Pandora wrote:Thanks!Suncho wrote:I think it's more accurate to say that if an object is still relative to you with respect to the three spacial dimensions, that object is moving through time at the speed of light. That same object is moving through time at a rate slower than the speed of light when viewed by an observer that is moving spacially relative to that object.
What still puzzles me is how the theory deals with situation in which it is ambiguous with regard to who is moving and who is still. Imagine two persons in deep space without any other frame of refernce flying past each other. For each of them it is as if they are moving and the other one is standing still (or vice versa, actually). In this situation, who has the faster speed through time and who through space?
So the answer is that the moving guy is always going slower through time than the stationary guy. Which guy is stationary depends on your frame of reference. =)
Ahh, I think i see the point you are getting at. The important thing to remember is that no matter how many frames of reference you have, one of those frames of reference will ALWAYS be defaulted back to when the experiment is over (where all the clocks are collected together again to be compared). It is THAT frame of reference which everything goes back to at the end of the experiment which indicates the "observer frame of reference" with which the calculations can then be done.Suncho wrote:B is also true. But forget about the spinning. Assume the earth is flat like a map. If you start factoring in spinning, acceleration, or gravity, we enter the realm of general relativity.Pandora wrote:Although it might be a stretch, the same question can also be posed for the example with the airplane and the atomic clocks. One might say (A) that the plane is moving faster then any place on the earth's surface. However, (B) from the plane's reference frame one would say that the plane is standing still, and the earth spins faster underneath it. As the experiment has shown, (A) is true. But why? How is something like this resolved?
oh man, on a notepad here i have written a whole rambling essay which concluded with the suggestion that TIME ITSELF has mass.
i'm not sure how good my reasoning is though, i'll have to check it against the answers to the questions above
.