It would seem that SiFi is more like prophesy or is that science just sets out to prove what the SiFi writers come up with.
And Sandoz (who invented LSD) is the most reliable and reputable outfit to get it from, but that was a looooong time ago.
Q: Can anything travel faster than light? A: No
- Thread starter earth_as_one
- Start date
And Sandoz (who invented LSD) is the most reliable and reputable outfit to get it from, but that was a looooong time ago.
s_lone, one has to be careful about such experiments, and what they really measure. As I said in my previous post, many paradoxes can occur near the speed o light. I remember reading once how speed of light may be exceeded.
The experiment is simple. Suppose we take a very tight laser with a long range. Suppose the laser is 10 cm long, and it casts a beam which is 1000 cm long. Hold a screen at 1000 cm, the laser beam will appear on it as a point of light.
Now, rotate the laser are 10% the speed of light (theoretically perfectly possible). The point of light on the screen will move at 10 times the speed of light, since at a distance of 1000 cm, the point will travel 100 times as fast as the tip of the laser.
Here apparently we have exceeded the speed of light, but it is only apparent. In reality, the speed of light is not exceeded, since the same photons do not travel the length of the screen. It is the different photons which strike different parts of the screen, so nothing is actually moving faster than light.
Now, I don’t know if the experiment described in space.com is simply smoke and mirrors or a real breakthrough, time will tell. But one must be cautious of any claims of exceeding the speed of light.
Last edited:
Speed does not depend upon wavelength, Liberalman.
Speed = Wavelength X Frequency
If wavelength is large, that simply means that frequency is low. Thus blue light has smaller wavelength than red light. But it also has higher frequency, so the speed of light is the same in both cases.
But there is one way to vary the speed of light. That is to use another medium than vacuum. If you use glass, water or any other medium, speed of light will be different there than the value in the vacuum (it will be lower, of course).
I think the news media are terrible at reporting science, and scientists are terrible at explaining science to the media, with a few notable exceptions like Carl Sagan, and what probably happened there was a failure to clearly distinguish among phase velocity, group velocity, and signal velocity. Unfortunately, I don't think I know how to explain those very well to a non-mathematical crowd. Loosely speaking, any signal is composed of a whole lot of waves of different frequencies and phases and they travel at different velocities through different media. I'm sure that makes it clear as mud. If you feel up to dealing with some relatively simple differential equations, have a look at this.
The key points of relativity are that the speed of light is the same for all observers, a consequence that actually follows from Maxwell's equations (known since the 1860s) where it appears as a numerical constant defined by the ratio of electrical to magnetic forces, and that the laws of physics must be the same for all observers. Not all motion is relative in relativity, only motion that's uniform in magnitude and direction. Accelerated motion is not relative, but the laws of physics appear different in accelerated systems so it's possible to distinguish between accelerated and uniformly moving systems. If the earth was alone in the cosmos, we'd still know it's rotating simply by observing that high and low pressure systems in the atmosphere rotate in opposite directions. They're a consequence of the Coriolis effect, which appears only in rotating systems. Rotation is an acceleration, which is simply a change in velocity, and velocity has both a speed and a direction, speed and velocity are not synonyms. A change in speed and a change in direction are both accelerations.
The laws of physics being the same for all observers just means that measurements of things like time and distance and velocity and mass will always have the same relationships among each other, but different observers will not in general measure the same values for them when observing the same events, unless they happen to be unmoving with respect to each other.
I think that answers most of the questions raised here, at least in a general way. I'll have a look back in the thread later to make sure, I'm a bit rushed this evening despite the apparent long-windedness of this, but if anyone's got any other questions, lay 'em out and I'll try to answer. No guarantees on timing though... :smile:
Two other points:
1. SJP's example of an observer seeing him get a beer before getting up off the couch is a reversal of causality, and for that to happen the observer would have to be going faster than light with respect to SJP.
2. light travels at different speeds through different media, fastest in a vacuum and slower in everything else, and a medium's index of refraction is a measure of that, more or less. Actually different frequencies travel at different speeds and the index of refraction is different for each of them, which is how a prism breaks up white light into a rainbow. It is, however, possible to get particles traveling through a medium other than a vacuum faster than light goes through it. In that event, a little cone of radiation spreads out behind each particle. It's called Cerenkov radiation, and accounts for the glow you may have seen in photos of radioactive stuff, like nuclear reactors and spent fuel bundles, sitting in water.
I've been mulling this over all day and have come to the conclusion there is one thing that travels faster than light----------- malicious gossip LOL
If two objects are traveling, both at a speed of light , what would be the speed at the point where the two objects pass one another .
Last edited:
That depends a lot on which way each is travelling..............a lot less than the speed of light for sure.
Shadows can travel faster than the speed of light. So can the dot from laser pointers. Even though the photons are travelling at the speed of light, the shadow/light-beam can have a tangential velocity greater than c.
Go back to school.
There's something called the refractive index. Light varies in velocity depending upon which medium it is in.
Do you ever wonder about stuff you say? If velocity did not depend upon wavelength then you equation is out-to-lunch.
Balogna, If wavelength is large, then either frequency is low or else velocity is different. wow What is this, grade 10 physics? and you still can't get it right?
Last edited:
You mean what would be the closing speed of the two objects? That would depend upon the relative angle from each other.
They would still approach each other at the speed of light, not at twice the speed of light. I know this sounds absurd, but one encounters plenty of absurdities when one approaches the speed of light.
This is one instance when 2 plus 2 does not equal 4, but equals 2.
Last edited:
Dexter, I remember reading a very interesting science fiction story based upon this principle. The writer had postulated a material he called ‘slow glass’. Light travels through slow glass very slowly, it may take 10 years to pass through a sheet of glass a few millimeters thick.
And he came up with an interesting application for slow glass. Place the sheet of slow glass in a strategic position in a spot of scenic beauty, with lakes, valleys, mountains etc. For 10 years, you wouldn’t see anything on the other side. After ten years, you will begin to see the scenery. Then the sheet of slow glass can be sold as a paining, mosaic, sculpture or whatever. The buyer will continue to see the scene of natural beauty for the next 10 years, and it will be ever changing scenery, a flock of birds flying, or snow falling in winter etc.
It will go on for 10 years and then the sheet of slow glass would become blank. Of course, one could purchase a mosaic which would last for 5 years, 10 years, 20 years etc. for different prices.
Indeed. That is the principle behind the example I gave, where one can apparently exceed the speed of light.
The speed of what, the objects? Objects with mass cannot travel that fast, they'd have to be photons, and they'd pass each other at light speed.
Many ways have been devised to measure the speed of light.
The first measurement of c on Earth was by Armand Fizeau in 1849. He used a beam of light reflected from a mirror 8 km away. The beam passed through the gaps between teeth of a rapidly rotating wheel. The speed of the wheel was increased until the returning light passed through the next gap and could be seen. Then c was calculated to be 315,000 km/s. Leon Foucault improved on this a year later by using rotating mirrors and got the much more accurate answer of 298,000 km/s. His technique was good enough to confirm that light travels slower in water than in air.
Time is relative to motion. Since we live on same planet, circling the same sun we all experience time the same way, creating an illusion of time being constant. A measurable difference in relative time can be observed on earth by putting atomic clocks on aircraft:
In 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40+/-23 nanoseconds during the eastward trip and should have gained 275+/-21 nanoseconds during the westward trip ... Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59+/-10 nanoseconds during the eastward trip and gained 273+/-7 nanosecond during the westward trip, where the errors are the corresponding standard deviations.
However, you would not measure a change in the speed of light in either aircraft... Because of the shift in time.
I stand corrected.
Electrons can travel faster than light by cheating...
The blue glow in this "swimming pool" nuclear reactor is Cherenkov radiation, emitted as a result of electrons travelling faster than the speed of light in water.