No the speed of light is constant. as said before, in something else than the vacuum, it looks differently, but this is an illusion
Light also travels in straight lines, but in a gravitational field you'll observe the illusion of light appearing to curve.
atoms are mostly made out of vacuum
So is a gravitational lens.
those (electrons in general, mostly bound to their atom) will oscillate in response and create an EM field on their own like new sources those sources will interfere with the original source and create a new overall pattern that we would call 'this is light traveling in this medium' This new wave is what can be seen as light going slower than c in this particular medium.
I don't buy it. See elsewhere for my response to that theory.
Completely wrong. A noteworthy journalist reports that the speed of light is actually 300,000 km/s
Can't be. The meter is exactly 1/299,792,458 of one light-second by definition. If we've measured the speed of light incorrectly, we have to change the length of the meter. Light will still go exactly 299,792.458 km/s.
Feynman replied that when light passes through matter, the charged particles in that matter oscillate in sympathy with the oscillations of the light's electomagnetic field. But because they are all in a bound state, and because accellerating charged particles causes them to emit light of their own, thereby carrying away energy and so dampening their sympathetic oscillation, the movements of the charged particles in matter is not quite in phase with the waves in the light passing through the medium.
Feynman concluded, "The light emitted by the charge particles in matter interferes with the light passing through the medium" - that is, wave peaks add to wave peaks, and so with troughs, while peaks and troughs together cancel each other - "so that the resulting combination of light waves only appears to move slower than C."
Thus the Photons are always moving at a constant velocity of C, but all the Photons in the medium interact so that passing a Photon through the medium will result in the exit Photon being delayed from the timing you would expect from when the entrance Photon entered the front surface.
I'm not sure I buy that explanation. To appear to move slower than C, the interference would have to exactly cancel out the light for
t >= distance / C, t < distance / speed of light in medium
and have exactly zero effect on the light for
t >= distance / speed of light in medium
Or in other words - if the first photon leaving the medium isn't the first photon that entered it, what happened to that photon? Why doesn't the same thing happen to the rest of the photons that enter the medium?
Anyway it would mean that transparent objects transmit light in much the same way as fluorescent objects fluoresce - which leads to all sorts of other questions, such as why in one the angle of light leaving is related to the angle of light coming in, but in the other the light leaving it is diffuse; and in one, the light produced is different in phase but in the same wavelength, but in the other the wavelength is different.
That was my first inclination too, but I did the math and apparently the scientists were too smart for that. (Italicized expressions can be plugged straight into Google.)
Assuming the distance is the curved distance (arc length): arc length in radians = 732 km / circumference of earth * 2 * pi 732 km / 40075.16 km * 2 * pi
Form an equilateral triangle with two sides with the length of earth's radius intercepting the 732km arc, and that angle between them. Angles in a triangle add up to pi, so the other two angles in the triangle are both: other angle = (pi - arc length in radians)/2. (pi - (732 km / 40075.16 km * 2 * pi))/2
Law of sines: straight-line distance = (radius of earth / sin(other angle)) * sin(arc length in radians) (6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi)
difference in distance = arc length - straight line distance 732 km - (6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi)
difference in time = difference in distance / c (732 km - (6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi))/c
According to Google, that's about 1.3485 microseconds. Obviously they couldn't have been using the arc length instead of straight-line distance or their error would have been much larger than 60 nanoseconds.
If, from your inertial frame of reference, the signal appears to be moving backward in time, you've violated causality in all frames of reference. According to Wikipedia:
since one of the two fundamental postulates of special relativity says that the laws of physics should work the same way in every inertial frame, then if it is possible for signals to move backwards in time in any one frame, it must be possible in all frames
Yes. Actually, the gravitational fields cancel. Within a hollow shell of homogenous density, they exactly cancel and you are weightless. In a homogenous sphere, you can solve the problem in two parts; the shell of material at greater radius from the center than you, and the sphere of material closer to the center than you. The gravitation from the shell is zero, so you're effectively in the gravitational field of a smaller sphere, the sphere composed of all the material closer to the middle than you.
(Since integrating the problem in polar coordinates converts it into infinitely many differential-thickness hollow spheres, all that matters is that each hollow sphere has a homogenous density. The overall density of the sphere need not be homogenous as long as the density is a function of radius and no other variables, because then it will break down into homogenous hollow spheres.)
For non-homogenous spheres, or for non-spherical shapes, the gravitational fields do not quite cancel out exactly, but there's still a similar effect when you get closer to the center.
Nope. The refractory index of a material is a ratio between the speed of light in the medium and the speed of light in air. Also, "light" does not necessarily or generally mean the visible portion of the electromagnetic spectrum. Most materials are transparent to at least part of the spectrum, so the local speed of light is applicable even to materials which are opaque to visible wavelengths.
Light is also affected by gravity, although this may be because space/time is warped by the gravitational field and from the photon's frame of reference it is traveling in a "straight" line. Only from an outside observer's frame of reference would its path appear to be curved. I personally think that this is also probably the most likely explanation for why the speed of light changes in non-vacuum... the strong fields generated by proximity of mass on an atomic scale curve or compress space/time within the material.
Not entirely your fault, perhaps - the person you were replying to seemed confused too. He used the terms "isopropyl alcohol", "industrial forms of ethanol", and "denatured alcohol" somewhat arbitrarily. In fact they are three different things. One is poison, one is not, and one wasn't until poison was added to it.
Both consist of a carbon atom attached to an -OH group. Carbon makes 4 bonds. In ethanol, the other 3 bonds are to two H and one CH3. In isopropyl alcohol, it is bound to one H and two CH3.
The Techspray in GP's link is not ethanol. Nor is it denatured ethanol (ethanol rendered undrinkable by adding poison). It is isopropyl alcohol (read the page - it's clearly labeled), and it is not safe for human consumption.
IDE-to-USB should be around for a while longer, I expect. Buy a stand-alone adapter, buy a USB enclosure kit for an IDE drive, or just rip apart an old USB hard drive - the drive inside it is either IDE or SATA.
Because it tends to break legacy DOS apps that use the mouse in text-mode, and the preferred behavior is that which doesn't break things by acting differently. If you want it to act differently, you have to explicitly configure it to do so.
Legacy DOS didn't natively support copy-and-paste at all... you had to do an >out.txt if you needed to capture the output. Then you could open it in your text editor of choice. Be glad you have it at all.
And the ability to change the colors of the command prompt was around long before Windows ever existed, using ansi.sys.
I thought Windows is not the hobby OS where you need to spend hours to tweak it until it works.
It works about the same as DOS ever did with no tweaking, and it has a few new features (such as copy-and-paste) which you can enable if you are inclined to do so. And if you do want to tweak it, I doubt that you could spend more than five minutes looking through the entire dialog to set the command prompt options. It certainly doesn't take "hours".
Can anybody give a brief summary of the differences between UltraDefrag, Defraggler, and the native defrag utility in Windows 7? The only difference I'm aware of is that the native utility only defragments entire drives, whereas the other two can defragment a single file or folder.
Slashdot Mirror
No the speed of light is constant. as said before, in something else than the vacuum, it looks differently, but this is an illusion
Light also travels in straight lines, but in a gravitational field you'll observe the illusion of light appearing to curve.
atoms are mostly made out of vacuum
So is a gravitational lens.
those (electrons in general, mostly bound to their atom) will oscillate in response and create an EM field on their own like new sources those sources will interfere with the original source and create a new overall pattern that we would call 'this is light traveling in this medium' This new wave is what can be seen as light going slower than c in this particular medium.
I don't buy it. See elsewhere for my response to that theory.
Completely wrong. A noteworthy journalist reports that the speed of light is actually 300,000 km/s
Can't be. The meter is exactly 1/299,792,458 of one light-second by definition. If we've measured the speed of light incorrectly, we have to change the length of the meter. Light will still go exactly 299,792.458 km/s.
Feynman replied that when light passes through matter, the charged particles in that matter oscillate in sympathy with the oscillations of the light's electomagnetic field. But because they are all in a bound state, and because accellerating charged particles causes them to emit light of their own, thereby carrying away energy and so dampening their sympathetic oscillation, the movements of the charged particles in matter is not quite in phase with the waves in the light passing through the medium.
Feynman concluded, "The light emitted by the charge particles in matter interferes with the light passing through the medium" - that is, wave peaks add to wave peaks, and so with troughs, while peaks and troughs together cancel each other - "so that the resulting combination of light waves only appears to move slower than C."
Thus the Photons are always moving at a constant velocity of C, but all the Photons in the medium interact so that passing a Photon through the medium will result in the exit Photon being delayed from the timing you would expect from when the entrance Photon entered the front surface.
I'm not sure I buy that explanation. To appear to move slower than C, the interference would have to exactly cancel out the light for
t >= distance / C,
t < distance / speed of light in medium
and have exactly zero effect on the light for
t >= distance / speed of light in medium
Or in other words - if the first photon leaving the medium isn't the first photon that entered it, what happened to that photon? Why doesn't the same thing happen to the rest of the photons that enter the medium?
Anyway it would mean that transparent objects transmit light in much the same way as fluorescent objects fluoresce - which leads to all sorts of other questions, such as why in one the angle of light leaving is related to the angle of light coming in, but in the other the light leaving it is diffuse; and in one, the light produced is different in phase but in the same wavelength, but in the other the wavelength is different.
That was my first inclination too, but I did the math and apparently the scientists were too smart for that. (Italicized expressions can be plugged straight into Google.)
Assuming the distance is the curved distance (arc length):
arc length in radians = 732 km / circumference of earth * 2 * pi
732 km / 40075.16 km * 2 * pi
Form an equilateral triangle with two sides with the length of earth's radius intercepting the 732km arc, and that angle between them. Angles in a triangle add up to pi, so the other two angles in the triangle are both:
other angle = (pi - arc length in radians)/2.
(pi - (732 km / 40075.16 km * 2 * pi))/2
Law of sines:
straight-line distance = (radius of earth / sin(other angle)) * sin(arc length in radians)
(6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi)
difference in distance = arc length - straight line distance
732 km - (6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi)
difference in time = difference in distance / c
(732 km - (6378.137 km / sin((pi - (732 km / 40075.16 km * 2 * pi))/2)) * sin(732 km / 40075.16 km * 2 * pi))/c
According to Google, that's about 1.3485 microseconds. Obviously they couldn't have been using the arc length instead of straight-line distance or their error would have been much larger than 60 nanoseconds.
What we consider vacuum might not be as empty as we think
Forget about dark matter; we already know what it's full of: gravitational fields. Does gravity affect light? Yes it does...
If, from your inertial frame of reference, the signal appears to be moving backward in time, you've violated causality in all frames of reference. According to Wikipedia:
http://en.wikipedia.org/wiki/Time_travel#Via_faster-than-light_.28FTL.29_travel
since one of the two fundamental postulates of special relativity says that the laws of physics should work the same way in every inertial frame, then if it is possible for signals to move backwards in time in any one frame, it must be possible in all frames
I thought it was also based off of being absorbed and getting retransmitted
No. That's called fluorescence. Refraction is completely different.
Yes. Actually, the gravitational fields cancel. Within a hollow shell of homogenous density, they exactly cancel and you are weightless. In a homogenous sphere, you can solve the problem in two parts; the shell of material at greater radius from the center than you, and the sphere of material closer to the center than you. The gravitation from the shell is zero, so you're effectively in the gravitational field of a smaller sphere, the sphere composed of all the material closer to the middle than you.
(Since integrating the problem in polar coordinates converts it into infinitely many differential-thickness hollow spheres, all that matters is that each hollow sphere has a homogenous density. The overall density of the sphere need not be homogenous as long as the density is a function of radius and no other variables, because then it will break down into homogenous hollow spheres.)
For non-homogenous spheres, or for non-spherical shapes, the gravitational fields do not quite cancel out exactly, but there's still a similar effect when you get closer to the center.
how in the hell is the ratio of mass to energy exactly the speed of light squared?
The same way that the ratio of mass to volume is exactly 1 gram per cubic centimeter of water.
Nope. The refractory index of a material is a ratio between the speed of light in the medium and the speed of light in air. Also, "light" does not necessarily or generally mean the visible portion of the electromagnetic spectrum. Most materials are transparent to at least part of the spectrum, so the local speed of light is applicable even to materials which are opaque to visible wavelengths.
Light is also affected by gravity, although this may be because space/time is warped by the gravitational field and from the photon's frame of reference it is traveling in a "straight" line. Only from an outside observer's frame of reference would its path appear to be curved. I personally think that this is also probably the most likely explanation for why the speed of light changes in non-vacuum... the strong fields generated by proximity of mass on an atomic scale curve or compress space/time within the material.
The speed of light in a vacuum (c) is a constant. The speed of light in a non-vacuum is not.
I don't believe a publisher would not be aware of Confessions of a Dangerous Mind
How was that unauthorized? Wiki says he sold the rights to it to Columbia Pictures.
It's not a fallacy when it's true by definition.
Can a true pacifist use lethal force? Can a true vegetarian knowingly eat meat? Can a true Christian willfully disobey parts of the Bible?
Not entirely your fault, perhaps - the person you were replying to seemed confused too. He used the terms "isopropyl alcohol", "industrial forms of ethanol", and "denatured alcohol" somewhat arbitrarily. In fact they are three different things. One is poison, one is not, and one wasn't until poison was added to it.
Oh, by the way that Techspray 99.8% alcohol is pure ethanol, not denatured
Ethanol = C2H5OH = CH3HCHOH
Isopropyl alcohol = (CH3)2CHOH = CH3CH3CHOH
Both consist of a carbon atom attached to an -OH group. Carbon makes 4 bonds. In ethanol, the other 3 bonds are to two H and one CH3. In isopropyl alcohol, it is bound to one H and two CH3.
The Techspray in GP's link is not ethanol. Nor is it denatured ethanol (ethanol rendered undrinkable by adding poison). It is isopropyl alcohol (read the page - it's clearly labeled), and it is not safe for human consumption.
It is very large, but also very compressible.
IDE-to-USB should be around for a while longer, I expect. Buy a stand-alone adapter, buy a USB enclosure kit for an IDE drive, or just rip apart an old USB hard drive - the drive inside it is either IDE or SATA.
I'm just explaining Thing 1's joke because you apparently didn't get it.
They still don't need space to contract. You could have left it off altogether.
Why is that all not enabled by default?
Because it tends to break legacy DOS apps that use the mouse in text-mode, and the preferred behavior is that which doesn't break things by acting differently. If you want it to act differently, you have to explicitly configure it to do so.
Legacy DOS didn't natively support copy-and-paste at all... you had to do an >out.txt if you needed to capture the output. Then you could open it in your text editor of choice. Be glad you have it at all.
And the ability to change the colors of the command prompt was around long before Windows ever existed, using ansi.sys.
I thought Windows is not the hobby OS where you need to spend hours to tweak it until it works.
It works about the same as DOS ever did with no tweaking, and it has a few new features (such as copy-and-paste) which you can enable if you are inclined to do so. And if you do want to tweak it, I doubt that you could spend more than five minutes looking through the entire dialog to set the command prompt options. It certainly doesn't take "hours".
Whoosh.
Files don't need more space to contract; they need more space to expand.
Sooner or later, high-gain audio sensors and computer voice processing will be added, and then you can be prosecuted for "cursing in public."
You are fined one credit for a violation of the verbal morality statute...
MyDefrag doesn't support boot-time defrag.
I really don't like the name either.
My Win7 computer came preconfigured to defrag on Wednesdays at 01:00, IIRC.
Can anybody give a brief summary of the differences between UltraDefrag, Defraggler, and the native defrag utility in Windows 7? The only difference I'm aware of is that the native utility only defragments entire drives, whereas the other two can defragment a single file or folder.