It's time for another physics question...
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It's time for another physics question...
...and I have to say, I have no idea what the answer is. This is all hypothetical too.
So, first of all, when there is a solar eclipse, and the moon is in between us and the sun, it's shadow is cast over 167 miles on the planet Earth, and it travels at 1,000 mph. This I do know, but it will help with my question.
Let's assume that an object like that moved at, or just about, the speed of light. How fast is that shadow travelling? Is it possible for the shadow to surpass the speed of light?
So, first of all, when there is a solar eclipse, and the moon is in between us and the sun, it's shadow is cast over 167 miles on the planet Earth, and it travels at 1,000 mph. This I do know, but it will help with my question.
Let's assume that an object like that moved at, or just about, the speed of light. How fast is that shadow travelling? Is it possible for the shadow to surpass the speed of light?
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From: DIXIE
The shadow would travel slower than the moon. Consider a wheel, the outside of the wheel is traveling much faster than the center hub. Since the moon orbits the Earth, the Earth is the hub. Therefore, the shadow that we see is moving exponentially slower than the moon. Consider this, How many miles does the moon travel for each mile the shadow moves?
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Hmm, interesting. I'm no expert but let see what I can do with this. A shadow is not a physical object, it is just the absence of light. The eclipse example makes things a bit more complicated - too many moving parts.
Imagine a light source 100 feet from, and aimed at a wall. A moving object half way between the source and the wall would cast a shadow which moves 2x the speed of the moving object. This is a big clue. Move the object closer to the light source (much different from the sun/moon/earth relationship) now the shadow's multiplier INCREASES. The shadow may now move 10x or 100x the speed of the object which is casting the shadow.
The shadow will decrease in size in the direction of travel of the casting object as it aproaches the speed of light - but only becasue the object itself changes dimensions. This is just more fun than it is relevent.
Ever wave a running garden hose back and forth? The stream of water appears to curve side-to-side. Infact, mostly, each bit of water travels in a straight line after exiting the hose. Since the speed of light is finite the same effect should take place, the shadow lags behind the object.
I say that yes, a shadow can move much faster than the speed of light. Any opaque object moving past a stationary light source casts a shadow with a lateral speed that increases as you get farther from the light source, beyond the speed of light without limit. The only reason it can do this, is because it's not a physical object.
I could be all wet though - don't try this on a physics exam!
Imagine a light source 100 feet from, and aimed at a wall. A moving object half way between the source and the wall would cast a shadow which moves 2x the speed of the moving object. This is a big clue. Move the object closer to the light source (much different from the sun/moon/earth relationship) now the shadow's multiplier INCREASES. The shadow may now move 10x or 100x the speed of the object which is casting the shadow.
The shadow will decrease in size in the direction of travel of the casting object as it aproaches the speed of light - but only becasue the object itself changes dimensions. This is just more fun than it is relevent.
Ever wave a running garden hose back and forth? The stream of water appears to curve side-to-side. Infact, mostly, each bit of water travels in a straight line after exiting the hose. Since the speed of light is finite the same effect should take place, the shadow lags behind the object.
I say that yes, a shadow can move much faster than the speed of light. Any opaque object moving past a stationary light source casts a shadow with a lateral speed that increases as you get farther from the light source, beyond the speed of light without limit. The only reason it can do this, is because it's not a physical object.
I could be all wet though - don't try this on a physics exam!
Last edited by BikerWithTruck; Feb 1, 2006 at 02:23 PM.
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BWT...I think everyone might be. This came up with my astronomy teacher, who is also a physics and astro-physics professor, and he stumped himself. You're right, the shadow has no mass, but what I think we kept getting stuck on, or what I am, is if that shadow is moving faster than the speed of light, what happens when it passes? Is there a lapse between the time it passes and the time it takes for the light to shine behind it again?
The whole eclipse thing was just for visual effect, even though that is a fact.
The whole eclipse thing was just for visual effect, even though that is a fact.
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Originally Posted by jdmorg
...if that shadow is moving faster than the speed of light, what happens when it passes? Is there a lapse between the time it passes and the time it takes for the light to shine behind it again?
The apparent effect to a viewer in the path of a shadow moving near, at or beyond the speed of light is likely this: If the shadow is not HUGE in the direction of travel then you never notice it. It's like how movies work, 60 frames per second is to fast too notice changes. The light cones and rods in your eye don't respond that fast. If the shadow is HUGE it would appear as 'instant lights off' when the shadow overcomes you, and 'instant lights on' when it has passed. This assumes you are on the plane of the shadow, and not observing it from a distance. I suspect that at a great enough distance one could observe a shadow moving at greater than the speed of light, but it would be so far away that it may not seem that impressive.
standard disclaimer.
Last edited by BikerWithTruck; Feb 1, 2006 at 03:04 PM.
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From: DIXIE
Now, when you talk about a shadow "moving" the only real part we would see or sense is the leading and trailing edge of the shadow. You would only see the absense of light, not the shadow itself. If the mass were travelling in such a way as to block a series of lazers that shone dots on a flat plane and the object was only large enough to block one lazer beam at a time, we would have to use very slow time motion photography to capture the "missing dot". Regardless of the amount of light or the size of the object, there would definately be a point at which the steady stream of light from the sun was blocked even if were for just a barely perceptable period of time.
Change the question a bit and see what you think of this. If a flat plane were to move into the stream of sunlight at the speed of light, instantly stop, then travel toward the earth at the speed of light, instantly change direction back out of the stream, would that be any different that it passing through the stream of light? To complicate the question more, if the flat plane travelled toward the earth faster than the speed of light, would it "push" the light to faster than the speed of light?
Change the question a bit and see what you think of this. If a flat plane were to move into the stream of sunlight at the speed of light, instantly stop, then travel toward the earth at the speed of light, instantly change direction back out of the stream, would that be any different that it passing through the stream of light? To complicate the question more, if the flat plane travelled toward the earth faster than the speed of light, would it "push" the light to faster than the speed of light?
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Originally Posted by jbabbler
Change the question a bit and see what you think of this. If a flat plane were to move into the stream of sunlight at the speed of light, instantly stop, then travel toward the earth at the speed of light, instantly change direction back out of the stream, would that be any different that it passing through the stream of light? To complicate the question more, if the flat plane travelled toward the earth faster than the speed of light, would it "push" the light to faster than the speed of light?
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Here's my take on it, for what it's worth.
I think of an example where a plane is flying overhead. For simplicity's sake say that the sun is directly overhead and the plane travels directly overhead. With a normal plane, when you look up you will see the plane block the sun and a shadow pass over you. Now, think of the beams of light as if they were drops of rain. Absent any wind (i.e. the rain is falling straight down) you would experience a moment when the rain is not falling on you, because the plane has blocked the rain for a second. This effect may happen a few seconds or minutes after the plane passes directly over head because of the speed of the plane relative to the speed that the drops are falling. As a plane approaches or passes the speed of light (if that were possible) this relationship of speed comes into play with the light taking the place of the rain drops. If the plane is moving faster than the speed of light, and you look up, you will still see a shadow. It may only last for a split second, but it will be there. How fast is it moving? Well it would be moving at the same speed as the plane, given the distance from the sun and the ground, there would be very little "multiplier" as discussed above. Now, because the plane is moving faster than the speed of light, it will not physically be located directly overhead when you look up and see it block the sun, but will be further along it's flight path. This is because the light takes time to reach you. Similar the way a jet airliner "sounds" like it's further back along it's flight when you look up and hear it. Because the sound takes time to reach you. The same principles apply to light.
Make sense?
I think of an example where a plane is flying overhead. For simplicity's sake say that the sun is directly overhead and the plane travels directly overhead. With a normal plane, when you look up you will see the plane block the sun and a shadow pass over you. Now, think of the beams of light as if they were drops of rain. Absent any wind (i.e. the rain is falling straight down) you would experience a moment when the rain is not falling on you, because the plane has blocked the rain for a second. This effect may happen a few seconds or minutes after the plane passes directly over head because of the speed of the plane relative to the speed that the drops are falling. As a plane approaches or passes the speed of light (if that were possible) this relationship of speed comes into play with the light taking the place of the rain drops. If the plane is moving faster than the speed of light, and you look up, you will still see a shadow. It may only last for a split second, but it will be there. How fast is it moving? Well it would be moving at the same speed as the plane, given the distance from the sun and the ground, there would be very little "multiplier" as discussed above. Now, because the plane is moving faster than the speed of light, it will not physically be located directly overhead when you look up and see it block the sun, but will be further along it's flight path. This is because the light takes time to reach you. Similar the way a jet airliner "sounds" like it's further back along it's flight when you look up and hear it. Because the sound takes time to reach you. The same principles apply to light.
Make sense?
Last edited by pitrow; Feb 1, 2006 at 03:05 PM.
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From: DIXIE
Originally Posted by BikerWithTruck
Huh? You lost me at "flat plane". Light speed (in a vacuum) is a constant meaning that it doesn't change, even if some flat plane is trying to push it around. I find it more productive to simplify questions rather than complicate them. Complicating things is easy and has less value. What if there were 17 flat planes each moving in a different direction and the light source was multi colored and rotating while orbiting 9 of the planes of which 5 had fuzzy dice hanging from them.... The answer is that Chuck Norris would just roundhouse kick the whole setup and there would be no more light - or shadows.
(AP) -- Scientists have apparently broken the universe's speed limit.
For generations, physicists believed there is nothing faster than light moving through a vacuum -- a speed of 186,000 miles per second.
But in an experiment in Princeton, New Jersey, physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering.
The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.
Researchers say it is the most convincing demonstration yet that the speed of light -- supposedly an ironclad rule of nature -- can be pushed beyond known boundaries, at least under certain laboratory circumstances.
This effect cannot be used to send information back in time," said Lijun ****, a researcher with the private NEC Institute. "However, our experiment does show that the generally held misconception that `nothing can travel faster than the speed of light' is wrong."
The results of the work by ****, Alexander Kuzmich and Arthur Dogariu were published in Thursday's issue of the journal Nature.
The achievement has no practical application right now, but experiments like this have generated considerable excitement in the small international community of theoretical and optical physicists.
"This is a breakthrough in the sense that people have thought that was impossible," said Raymond Chiao, a physicist at the University of California at Berkeley who was not involved in the work. Chiao has performed similar experiments using electric fields.
In the latest experiment, researchers at NEC developed a device that fired a laser pulse into a glass chamber filled with a vapor of cesium atoms. The researchers say the device is sort of a light amplifier that can push the pulse ahead.
Previously, experiments have been done in which light also appeared to achieve such so-called superluminal speeds, but the light was distorted, raising doubts as to whether scientists had really accomplished such a feat.
The laser pulse in the NEC experiment exits the chamber with almost exactly the same shape, but with less intensity, **** said.
The pulse may look like a straight beam but actually behaves like waves of light particles. The light can leave the chamber before it has finished entering because the cesium atoms change the properties of the light, allowing it to exit more quickly than in a vacuum.
The leading edge of the light pulse has all the information needed to produce the pulse on the other end of the chamber, so the entire pulse does not need to reach the chamber for it to exit the other side.
The experiment produces an almost identical light pulse that exits the chamber and travels about 60 feet before the main part of the laser pulse finishes entering the chamber, **** said.
**** said the effect is possible only because light has no mass; the same thing cannot be done with physical objects.
The Princeton experiment and others like it test the limits of the theory of relativity that Albert Einstein developed nearly a century ago.
According to the special theory of relativity, the speed of particles of light in a vacuum, such as outer space, is the only absolute measurement in the universe. The speed of everything else -- rockets or inchworms -- is relative to the observer, Einstein and others explained
For generations, physicists believed there is nothing faster than light moving through a vacuum -- a speed of 186,000 miles per second.
But in an experiment in Princeton, New Jersey, physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering.
The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.
Researchers say it is the most convincing demonstration yet that the speed of light -- supposedly an ironclad rule of nature -- can be pushed beyond known boundaries, at least under certain laboratory circumstances.
This effect cannot be used to send information back in time," said Lijun ****, a researcher with the private NEC Institute. "However, our experiment does show that the generally held misconception that `nothing can travel faster than the speed of light' is wrong."
The results of the work by ****, Alexander Kuzmich and Arthur Dogariu were published in Thursday's issue of the journal Nature.
The achievement has no practical application right now, but experiments like this have generated considerable excitement in the small international community of theoretical and optical physicists.
"This is a breakthrough in the sense that people have thought that was impossible," said Raymond Chiao, a physicist at the University of California at Berkeley who was not involved in the work. Chiao has performed similar experiments using electric fields.
In the latest experiment, researchers at NEC developed a device that fired a laser pulse into a glass chamber filled with a vapor of cesium atoms. The researchers say the device is sort of a light amplifier that can push the pulse ahead.
Previously, experiments have been done in which light also appeared to achieve such so-called superluminal speeds, but the light was distorted, raising doubts as to whether scientists had really accomplished such a feat.
The laser pulse in the NEC experiment exits the chamber with almost exactly the same shape, but with less intensity, **** said.
The pulse may look like a straight beam but actually behaves like waves of light particles. The light can leave the chamber before it has finished entering because the cesium atoms change the properties of the light, allowing it to exit more quickly than in a vacuum.
The leading edge of the light pulse has all the information needed to produce the pulse on the other end of the chamber, so the entire pulse does not need to reach the chamber for it to exit the other side.
The experiment produces an almost identical light pulse that exits the chamber and travels about 60 feet before the main part of the laser pulse finishes entering the chamber, **** said.
**** said the effect is possible only because light has no mass; the same thing cannot be done with physical objects.
The Princeton experiment and others like it test the limits of the theory of relativity that Albert Einstein developed nearly a century ago.
According to the special theory of relativity, the speed of particles of light in a vacuum, such as outer space, is the only absolute measurement in the universe. The speed of everything else -- rockets or inchworms -- is relative to the observer, Einstein and others explained
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this is just my opinion and probably a simplistic view, but at the risk of getting killed here goes. i don't see how a shadow could ever travel faster than the speed of light, as it is a lack of light.. it can only travel as fast as the entity that created it. the speed of light is a constant, so the lack of light should be as constant. i just can't think of any senerio where the source of a phenomena would be slower than the result of that source. i await the beatings and look foward to the lesson i'll soon get
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Originally Posted by pitrow
If the plane is moving faster than the speed of light, and you look up, you will still see a shadow.
2) If an airplane could travel faster than light, you could not see it at all. As an object reaches the speed of light they are compressed to zero length in the direction of travel. This might be the "flat plane" the jbabbler was talking about! Aint this fun?
3) Even if you ignore #2, at 30,000 feet altitude (or less) an airplane traveling at 186,000 miles per second would pass by faster than your vision could appreciate it. Again you see nothing.
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From: Joppa, Maryland
Bikerwithtruck: you said that if you move an object half way between a light source and whatever the light is hitting the shadow will move at 2x the speed of the object, right? So wouldn't you just take the object up to 93001 mps and move it by?
or if you move it close to the light source to make the shadow move at 100x than you would only need 1860.1 mps.
Theres probably some big glaring hole in this idea, but i thought i'd give some input.
or if you move it close to the light source to make the shadow move at 100x than you would only need 1860.1 mps.
Theres probably some big glaring hole in this idea, but i thought i'd give some input.
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From: Burlington Vermont area
Originally Posted by jbabbler
Now now, No reason to be condesending. read this before you go on speaking of things you don't completely understand...
I speak of things I don't completely understand all the time. It seems that it's often a mistake to think that one completely understands anything. To me the imoprtant part is knowing that I don't completely understand, and working at it.
I'm familiar with the article you pasted as well as other similar research at UC Berkley going back 5 or six years as I recall. It's fascinating. You must be a science fan too. That's great - I say lets all learn together!
It does appear that reliable sources are ripping up 100 years of Einsteins rule. I didn't think I'd live to see that happen. But if you're a scientist, you have to be prepared to re-examine long held beleifs in light of new evedence (pun intended). For the purpose of this discussion I think we can safely overlook chambers filled with vapors of cesium atoms since space is certainly not that.
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From: Burlington Vermont area
Originally Posted by captain p4
Bikerwithtruck: you said that if you move an object half way between a light source and whatever the light is hitting the shadow will move at 2x the speed of the object, right? So wouldn't you just take the object up to 93001 mps and move it by?
or if you move it close to the light source to make the shadow move at 100x than you would only need 1860.1 mps.
Theres probably some big glaring hole in this idea, but i thought i'd give some input.
or if you move it close to the light source to make the shadow move at 100x than you would only need 1860.1 mps.
Theres probably some big glaring hole in this idea, but i thought i'd give some input.