Another paradox :) Scientists couldn't accept it. Einstein embraced it. Don't worry, we're not going to see how he solved it quite yet...we're just going to see the paradox. Which is always more fun.
About a hundred years ago, scientists were sort of embarrassed. You see, they had just discovered something wierd about the speed of light -- it's always the same to you, no matter how fast you're going. But it didn't make any sense to then.
Baby Einstein wondered...what would happen if you ran the speed of light? You could "race" a beam of light, catch up to it, and run alongside it (like running alongside a bike).
What would stop you?
Unfortunately, as they found out, light is pretty stubborn.
First, a few notes -- We're going to be discussing the speed of light in a vacuum, unaffected by outer forces. We're not talking about light slowed down or sped up by the materials it is traveling in, or even reversed as some have claimed it. You'll see why later, but basically we're talking not so much about light itself but more about the "universal speed limit".
So, one day our friends Steven and Anne were once again bored, so they decided to play Catch. Things were going fine until Steve all of a sudden decides to throw a rock at 25 mph towards Anne. Anne, being a girl, runs away at 5 mph.
How fast will the rock approach Anne? Well, to Anne, the rock is catching up to her at 20 mph (25-5=20). As you run 5mph away from a 25 mph object, then it catches up to you at 20 mph. With me so far?
So now Anne is mad. She pulls out a rifle and lets one loose on her pal Steven. Steven runs away a bit faster...10 mph. However, the bullet is traveling at 900 mph. Steve is running away at 10 mph, so the bullet approaches him at 890 mph.
Then Steve pulls out a flashlight and shines it at Anne. He knows that Anne has spontaneously developed a severe allergy to light...so she doesn't stand a chance! The light travels at 670 million mph. She starts running away at 5 mph...so then the light should approach her at approximately 669,999,995 mph...right?
Until she comes to a starking realization. Even though she's running away at 5 mph, the light is still catching up to her at 670 million mph!
So she jumps on the Millenium Falcon, which speeds away at 170 million mph. So the light should be catching up to them at 500 million mph, right (670-170=500)? Just like how if you run away from a 67-mph car at 17 mph, the car catches up to you at 50 mph.
But, to Han Solo's surprise...this isn't true. Light is still catching up to him at 670 million mph!
Impossible?
In response, Han picks up the speed some more...and pumps the falcon's speed to 570 million mph. At this rate, light should catch up to them at a feeble 100 million mph. But...no! The light again catches up them at 670 million mph, again.
Did light speed up? No...from Steve watching from the sidelines, the light has been going at the same speed all along. But it's obvious that the light that Anna sees is traveling faster than the light that Steven sees...
WTF is going on?
a quick summary - No matter how fast you go, light always catches up to you at 670 million mph.
It's a simple fact. But do you have trouble believing it? So did the scientists 100 years ago. You can see why they were all jealous of Einstein when he cracked the mystery...which is what we'll be doing later.
--
If there is anything here that you didn't understand, if you believe that I am dreadfully incorrect on some accounts, or if you just want to comment, please leave a comment :) I'd be happy to take it, and I'd appreciate it a lot.
(Note - On November 7th, 2006, I finished the sequel to this post - A Glimpse of Time Dilation.)
Wednesday, November 01, 2006
Chasing a beam of light
Subscribe to:
Post Comments (Atom)
17 comments:
I don't believe that is true, so let me give you an example. You look up at the night sky and see a star that is ten light years away. This means that it took the light from that star ten years to reach your eye. A star that is 20 light years away apears to be right beside the ten light year star. Now the light fron the first star takes ten years to reach your eye and the second star takes 20 years to reach your eye. Now lets say both stars were born at the same time . Are you saying that the star thats 20 light years away will only take ten because its chasing the light from the other star. Obviously not
I'm not quite saying that.
First of all, let's establish that what you are saying is true. If you go out tonight, the light you see from a star 10 ly away is light that was emitted 10 years ago, and the light from a 20ly-away star was emitted 20 years ago.
Now, let's look at two space ships that are launched from the two stars at the same time and headed straight for Earth at .5c (half the speed of light) relative to the earth-stars system.
From the point of view of the space ships, the two ships are stationary relative to each other.
There is no relativity to take account here, because the two ships are operating from identical inertial reference points!
Where is the relativity occurring?
Let's say Spaceship A (from the farther star) shines his headlights at Spaceship B (from the closer star).
If you're watching these spaceships at the earth-and-stars reference frame, you'll see a .5c spaceship shooting out light, that travels 1c. The light's only moving .5c faster than the spaceship, to you.
If you're on Spaceship A, you'll see your headlights shooting out at, not .5c, but 1c. That's because time slows down for you, and you see the light moving faster because of that.
I have to respectfully disagree with that also. If that were true there would be no such thing as the "dopler efect". You're talking about time as if it were something physical when in fact it is just a concept . The physical stuff in this equation isn't that strange. Both spaceship A and B are traveling at .5c and since light can only travel at the speed of light it would take twice as long as normal for the light to reach the spaceship. This is because of the physical charactoristics of light and the medium that it travels in.Keep in mind that it traveled twice the distance to reach it though. However I do agree that time as it is percieved on the spaceship slows down but not actually.
My friend, it would take twice as long as normal for you, who are watching them while at rest with earth-star system. But what if you're on the ship, and you see you and the other ship as stationary?
If time truly were fixed, you would be saying "Wait, why is light moving twice as slow for me?", would you not?
Let's say there were two spaceships sitting stationary, 10 light years apart. One shines their headlights at the other, and the light takes "twice as long as normal" to get from one to the other, in a vacuum.
What is happening here? Did the did the astronaut just witness light that traveled slower than the speed of light?
What actually happens is that the astronaut witnesses the light traveling from his ship to the other ship taking 10 years, like it should.
This effect, though on a smaller scale, has been experimentally verified. In fact, it was experimentally verified in the late 1800's, which puzzled scientists quite a bit. I made a post on Einstein's solution; the link is at the bottom of this post.
You mention two stationary ships 10ly apart and they experience light traveling slower. Well that's just not true because that's the same as the light leaving the sun and hiting the earth which by the way is traveling pretty fast spinning in the Milky Way and which ever other way it's traveling in the universe. How would we be able to make heads or tails of anything in the universe if we had to acount for time changing because the earth and the sun and the milky way are moving.In my oppinion time is the constant and everything else can change including the speed of light. Why should the speed of light be constant in fact it is not . It depends on the density of what it is traveling in is.Light is energy like the rest of the material world is, and it travels like a wave in the medium that fills the universe not in a vacuum. When you make that medium less dense by introducing matter/energy light travels slower.Theoretically light can travel faster than we experience it if it were to travel in a more dense medium vacant of energy.
Your opinion is rooted in everyday newtonian physics and common experience, so it's very understandable.
However, what I am mentioning isn't just theoretical, or opinion. What I am mentioning are results that have been experimentally verified. They have measured the speed of light at varying velocities in vacuum, and they have found that it is constant.
Even the Earth is moving at 30 km/s around the sun. The sun itself is moving 220 km/s around the galaxy. If spacetime is truly fixed, where is "stationary"? Is it at the galaxy's center? Because if so, we'd be experiencing light that was 220 km/s slower in the direction of the sun's motion through the milky way, right?
Nope. In fact, they've never experienced a change over 1 m/s out of the 299,792,458 m/s, and that doesn't even depend on the direction they measure it in.
Also, it's a common misunderstanding about how light propagates through a medium. When light hits, say, glass, it doesn't just pass through. It hits the first atoms, which absorbs it and then retransmits new photons to the next atoms (while absorbing some), then to the next, etc. It's the same in any gas, such as air. Transparent materials basically just materials that retransmit a lot more than they absorb.
However, moving through materials this way obviously slows down the rate in which the information that light carries moves through the material. It has to be picked up and reabsorbed and retransmitted for every atom, etc. Even in water, this delay is detectable by the eye in something called refraction.
What we are interested in is the spirit of light from atom to atom. Because...how much more of a vacuum can you get, when you're in between atoms? That's the speed of light in a vacuum.
Justin, I like talking to you and this is an interesting subject but let me introduce something a little different.What if the universe is not empty, not a vacuum but instead it is a fluid medium. Now consider that what we know as matter is really energy packaged in different ways and sizes, building blocks of energy if you will. This energy spins and it moves and it displaces the fluid that fills the universe, but it can't hold it back , after all it's moving and you have the weight of the whole universe pushing back. Now think of light as a wave in this fluid. Light leaves the sun and ripples through the universe unless you take away what it travels in, just like sound waves stop if it encountered a vacuum (of air). Now what would be a vacuum of the mystery fluid....it would be matter, but not all matter just matter that is dense enough (or energy filled enough) to displace enough of this fluid as to create a vacuum so to speak. In fact matter does stop light and matter that is not dense enough or is configured in such a way that it lets light pass through still is enough to slow it down.
Looking at it this way also explains other forces that are elusive to understand such as gravity and magnetism. These can be looked as a wave in the fluid (magnetism) of simply the weight of the fluid poshing down on you ( gravity).. Tell me what you think
It has been a rather enjoyable conversation, i will admit.
If dense matter displaced this fluid, then why are some dense things transparent? Or why are some things that are less dense than glass opaque?
If the universe is filled with a fluid medium, would not we on Earth be travelling through it? A sort of "wind", you could say.
And what about the solar system? The solar system is flying at about 220 km/s through the gravity, carrying us with it. Surely, if the universe were filled with this fluid, we'd be moving through it. At around 220 km/s, at least, at times. That's pretty fast.
So we have this fluid blowing at us at 220,000 m/s. The same way wind blows at you at 80 km/h if you're in a convertible traveling 80 km/h. Let's propose a test to see if this fluid exists.
1) Send a beam of light in one direction in the wind, while you're traveling at a certain speed.
2) Send a beam of light in another direction in the wind, while you're traveling at another speed.
3) Actually, if there is any difference between the two, then yes, light does change based on how fast you are going.
However, scientists performed this experiment. And did you know what they found?
The difference in the speeds was 10,000 times smaller than they had anticipated...and that difference was random, due to experimental errors.
Light is constant at all velocities; it is fun to think about other frameworks, but you can't turn your back on experimentally verified data.
Transparency can be explained by chemical structure.The crystaline nature of certain substances allow the space between the atoms to be sufficiently big enough to allow the fluid medium to be in there and remember the light doesn't go through there unchanged.
Think about this you drop a stone into a pool of water and it creates waves of concentric circles and then you drop another stone beside the first one and the same thing happens. The waves created by both stones travel at the same speed and are not hindered by each other even though they intersect each other. There speed doesn't change . they just travel until the energy dissipates . The only way you can stop it is if you take away the water. Light has a maximum speed because of the physical characteristics . How do you know that the spinning of the sun and the earth proximity doesn't cause some kind of wave and this wave contributes to gravity. Magnetism is a wave in something. (what is it) Nobody knows what gravity is or magnetism for that matter. In fact they had to invent the nonsense of gravity waves because heaven forbid one of the weakest forces is faster that light. We've been programed to think of gravity as a pulling force even though every force in the universe pushes. You could tell everybody in the world that we landed on Jupiter and then argue,a week later, about how ridiculous that is and you wouldn't be able to convince everyone be cause people are hardwired to believe the first thing they hear.
Before you read experimental data try to rid yourself of prejudice that might skew that data.
You obviously know more about these subjects than I do. I just look at something and ask does it make sense, when it does that's fine but when it doesn't I don't just accept it , even if Einstein said it and you have to admit there is an awful lot about the way the universe is described that doesn't make sense that's why we have paradoxes. I think when you have a paradox something might be wrong with the way we look at it.
Your theory is interesting, but that doesn't explain how things much, much less dense than glass (say, paper). or manage to be opaque when their atoms are more spread out than even glass's atoms.
Anyways, about the experimental data --
These experiments were carried out by people who tried to prove that light is a wave in a medium. They set out determined to prove it. They believed it with all of their hearts and they spent their whole lives building a framework around it and studying it.
Do you think they had prejudice?
In science, we have something that is called peer-review. This is that in order for anything to be vaguely accepted, it has to be published and subject to scrutiny by every scientist in the field.
Science at that time believed in the fluid, and every scientist set out to prove these ones wrong. To prove that their experiments were due to an error and that "luminiferous aether", as they called it, was where light traveled.
Time and time again, they've tried to prove the existence of a fluid by measuring the aether wind. They've used more and more accurate devices to try to say "You guys were wrong. There has to be a fluid." But so far, nobody has been able to produce any evidence, despite nearly 200 years of experimentation and searching for it. Even these people who so adamantly believed in it that they would spend their whole lives studying it couldn't find any evidence of it when it came down to experiment.
What could possibly explain this experiment or skew this data, other than the absence of aether?
Fortunately, Einstein did not leave the paradox as I have stated it in this post. He later on explained it. I've posted about it here: http://cosmicoeuvre.blogspot.com/2006/11/glimpse-of-time-dilation.html
His explanations make a lot of sense. They explain everything and why everything happens, all under a simple framework.
btw, you can read more about the experiments testing about aether here:
http://en.wikipedia.org/wiki/Michelson-Morley_experiment
The transparency of glass has to do with the matrix that it's molecules line up in. The molecules in paper are all over the place making it more likely that light , which travels in a strait line,will hit it.
It's true that the aether (as it was called) may be difficult to detect or prove, but I don't see the same scrutiny given to explanations about gravity or magnetism. When scientist say that gravity is a force that pulls from the center of the earth there is no one that can explain the mechanism (what is pulling , how does it grab on to things why does it seem to pull harder on heavier things) there is no proof , no explanation, just a blanket statement ( gravity pulls) no one questions it . The difference is that theory equally has no evidence but is not discarded. I can make the same argument about magnetism which they also have no credible explanation about what it is. I offer an explanation that is more credible but because you can't detect the aether the theory is discarded. What I am saying is that whatever is "pulling" is also not detected as of yet but some people have the licence to create the nonsense of gravity waves so it's hard to argue with someone that is so rooted in there convictions that they have to fabricate evidence to support it. ( I'm not talking about you, it's been a pleasure talking with you about things. I can tell you have an open mind even though you argue your beliefs passionately.
Think about the example I gave you about the waves in water. Intersecting waves do nothing to each other just like intersecting light. You have light waves , radio waves, all kinds of different waves traveling in every direction all around us not interfering what so ever with each other unless you put something in front of it that it can't travel in.
Back to the speed of light. If you were in a spaceship traveling at the speed of light wouldn't it be more likely that if you looked behind you , you would see darkness because light couldn't catch up to you. What if you were going twice the speed of light would it catch up to you then . How do you wrap your mind around that. Light can not travel faster than it's physical properties and time is a man made concept so you can say a second is a year and it makes no difference and changes nothing. If you want to explain things that you don't understand (not you) you have to do better than fixing the books. Slowing down or traveling in time is science fiction.
My apologies; my argument about paper and glass was not sound.
There are frameworks of gravity that offer an explanation. I explain it in my post at http://cosmicoeuvre.blogspot.com/2006/11/gravity-and-fabric-of-spacetime.html , where gravity is suggested to be a warping of space-time. How mass scrunches together the very reality of space and time, and that curvature results in otherwise straight paths becoming curved by gravity.
That could have been left as a guess. A fanciful thought experiment, an imagination. Someone could have said "What if...?" and that would be the end of it.
What makes science science is that things aren't accepted until they are testable.
Someone goes, "What if _____?"
And science goes, "Well, if that were true, then __(a)__. If that wasn't true, then __(b)__."
Experimenters would then go, "Well, we found out that __(a)__ happened, and __(b)__ didn't happen."
Science says, "Your ideas are pretty cool."
This isn't the only way to gain knowledge. I'd be the last one to argue that. It's just the framework of obtaining knowledge that people gave a name too, called "Science".
Here's the idea:
"What if time slowed down when you are going faster?"
Instead of saying, "That's impossible," scientists say, "Well, if that were true, then if you put a clock with x accuracy on a plane and fly it really really really fast, and leave a clock with x accuracy on the ground, if the fast clock actually ends up slower than the ground clock by more than x accuracy (say, 10*x), then one of the possible explanations is that time slows down at higher speeds."
And then experimenters say, "Ok cool. Let's try it."
So they tried it, and it happened.
Scientists say, "Hey, your ideas are pretty cool. All of your mathematical predictions lined up. But just to be safe, we could use some more evidence. Let's say we had a particle that was timed to live exactly x seconds. All experiments we've done have proven it so far. Now, let's shoot that particle at 99.5% the speed of light. According to your equations, time would slow down about 10x to that particle. So it'd die after 10*x seconds."
Experimenters go, "I love shooting stuff really really fast. Let's try it!"
So they do it, and they come back and go, "This is very odd. Our particle, which has always died in x seconds, actually lived ten times longer when it was moving at 99.5% the speed of light. Very odd indeed! Its as if its internal time bomb was 10x slower when it's moving faster."
And science goes, "I think you're onto something here with your ideas."
And what if, someone else comes up, and says, "but wait! I think that time does not slow down at faster speeds!"
Science goes, "Okay. If that is true, then clocks wouldn't turn slower at faster speeds, and that muons (the time-bomb particle) would die regardless of their relative velocity. (Keep in mind Gallilean invariance: that experiments conducted in a system at a fixed velocity act exactly the same as they do at rest)"
Experimenters go, "You're on it!"
And they do the experiments again (for some reason). And...everything they'd expect to find does not happen. At all. Clocks don't stay the same at faster speeds, and muons turned to to last longer at fast velocities!"
Science would say, "Unless you can explain these phenomenon, your theory is of less value to us than the ones that can."
What if there were a physical reason why things take longer when you're going fast instead of implicating something like time, which doesn't exist.Time is not a physical thing , you can't touch it, you can't smell it, you can't taste it, you can only contemplate it.We should be asking what is slowing things down then you might find out why, instead of cooking the books to explain things we don't understand.
When someone says what if______? and science says well if that's true then ___a____ . Science should make sure it's assumptions are true first.
As far as the two experiments that you mentioned , I don't know any particulars about them and they sound pretty complicated but I have to tell you the one about the particle lasting longer sounds very suspect.
Justin, you make very good arguments and you are not combative. I'd like to throw some other ideas I have at you and see what you think. My name is Nick. I can talk about light and time, I just can't figure out how to post my comment with my name attached.
If you're suggesting that things behave differently at different velocities, then you're defying one of the most fundamental principles of physics: variance.
Let's say there are two rooms that are identical. They have no windows or anything that can let you see how things are outside.
Now, put one room on a perfectly smooth train track, moving at 30 mph.
Let's say you wake up in a room, but you don't know which. Galilean equivalence states that there are no experiments that could possibly be done that allows you to tell which room you are in.
If you say that there are no perfectly smooth train tracks, then let's say that that room is instead flying through space at a fixed speed, 30 mph (with the same gravity, somehow).
There literally are no experiments that could possibly done aside from breaking out of that room to tell whether the room you are in is moving at a fixed velocity or stationary.
This is a product of conservation of momentum. I could explain it more deeply here, but I think that if you think about it for a bit, you will see that the principles of conservation of momentum imply Galilean equivalence.
This is to say, if Galilean equivalence did not exist, there would be no conservation of momentum.
Muons are in such a state. Whatever velocity they are moving at, they act, internally, unchanged. What else would change them? Would they get buffeted by air? Muons are thousands of times smaller than a single air molecule.
Either way, even if something about their velocity was slowing them down, let me tell you what you are actually saying.
Either:
1) Special relativity accurately predicts the phenomenon, with exact mathematical predictions, down to the fifth decimal place, because it's true
or
2) There are forces at work which we do not know that magically, somehow affect these phenomenon exactly how special relativity would predict them to act, down to the fifth decimal place, by sheer coincidence.
Your unknown phenomenon are somehow affecting these experiments exactly the way that Special Relativity predicts they would.
If the results of the experiment were due to your odd forces, what are the chances that they exactly line up with Special Relativity?
I would understand your suggestion that objects behave differently at different velocities, because the velocity is somehow affecting how they work. That's cool. Maybe the plane's shaking or something makes a clock run slower, not the moving itself. Maybe muons know they're going faster and live longer. Maybe there is a fluid that jams the clock up when you go faster.
But if that were true, why is it that the results line up exactly with Special Relativity's equations?
Keep in mind, these are predictions. Scientists didn't just run the experiment and go "okay, how can we make our formulas produce this number somehow."
Instead, they made the formulas first, predicted the slow-down, and then tested them. It was exactly how they predicted.
So, if there were forces at work that jam up the clock or give youth the the muon...why is the time dilation exactly as special relativity says?
I'd love to hear your ideas, Nick. It's been interesting boiling down what science actually is in order to get down to the very fundamentals of what i'm trying to say.
Justin, this is your most compelling argument yet I don't know enough about the experiments to be able to comment. You've actually stumped me. I'll have to edjucate myself some more on the subject, but here is an experiment that could be done. Take two identical twins at birth and have one stay in Boston and have the other fly to Los Angelas and back every week and see which one lives longer.People on both sides of the argument might say there are a lot of facters that could makes someone die but if you do it with a big enough group of twins you probably would get good data. After all you should be able to predict how much longer the fying twin should live. In fact why not use data that we already have with frequent flyers all over the world.
On a totally different subject I want to fly this by you.
Most of the land on earth is located in the northern hemisphere. I want to offer a possible reason why that is. We all know that there are techtonic plates that are floating and moving and pushing up against each other. This is what causes mountains and volcanos (not the same thing but caused by the same thing). We also know that the earth is tilted and spins on an axes ( nothing to do with the spin) . The earth also revolves around the sun but not in a perfect circle, it revolves in an elipse getting closer the the sun then farther away. Now, the time when the earth is closest to the sun is during our winter when the northern hemisphere is tilted away from the sun. I propose that over a very long period of time the centrifical force of the earth speeding up when it whips around the sun so to speak make the techtonic plates slide to the northern hemisphere which is tilted away from the sun.
Now, I'm not a scientist but I've researched this a little and found some evidence that most of the volcanic eruptions and earth quakes occur between three months before and three months after the winter solstice. Perhaps the extra pressure brings the mounting tention to a breaking point.
What do you think?
Your experiment doesn't quite work (although it's a good start), because time dilation is almost unnoticeable at humanly achievable speeds. Time dilation is measured at fractions of the speed of light.
Airplanes travel at 260 m/s, which is a far cry from the 299,792,458 m/s of light. Time dilation factor is 1/(square root of (1 - v^2/c^2)). You'll notice that as v gets smaller relative to the speed of light, that number approaches 1/(1-0) = 1/1.
If you plug in 260 m/s there, you'll get that time on an average 747 airplane slows down by about factor of 1.0000000000003760757189463351795. If you somehow knew that the two twins would die at exactly eighty years of age, time dilation would make one live 0.00094879 seconds longer than the other. In fact, if you knew that the twins would live to be exactly 800 years of age, time dilation from an airplane would cause their deaths to differ by .1 seconds.
And that's if they're flying at every second, at the same velocity, for their entire lives.
Now, let's say that twin was out in orbit, traveling at 7859 m/s (the average orbiting space shuttle's speed). In that case, time dilation is a factor of 1.0000000003436079284607947049916. In this case, twins living exactly 80 years would die 0.867 seconds apart. We could always blame that difference on different eating habits, exercise habits, living in space, etc.
In fact, if you wanted them to differ in death by 1 second, they'd have to be moving at at least 8499.29 m/s, -- that's 5.3 miles per second.
As for your suggestion, a lot of it sounds interesting.
As for plate tectonics, one would think that the continents would tend to move northward over time; however, since Pangea, any of the continents have moved southward. The major movement of the northern hemisphere continents hasn't been northward, but east- and westward.
But I can't claim to be anyone who has studied these; honestly, I am unqualified to comment on any sort of geology beyond the high school level.
But a lot of your suppositions make sense. The next step would be -- instead of finding things and making them fit into your theory --to make testable predictions beforehand, and try to prove them.
I'll take that .0009 seconds dialation, I'm not getting any younger.
As far as the movement of the techtonic plates in other directions that has more to do with the position of the cracks between the plates. What I am saying is that one of the forces could be centrifical force. The only evidence that I can think of is the occurance of earthquakes and volcanic activity coinciding with the speed up of the earth, and again that has to be over time because there are other factors that would determine when an earthquake would happen . The tipping point could theoretically happen at anytime. That doesn't mean that it hasn't moved in other directions throughout earth's history, as I understand it the earth's axis has shifted from time to time. Maybe there would be a way to look at the position of the continents through out all the shifts, but that's way out of my leage.
Post a Comment