I disagree with einstein..

[dextrous]

The speed of light is constant relative to any moving object - this is what was (sort of) demonstrated by the michelson-morley experiment when they were searching for the aether.

Where your reasoning falls down CJ is the implicit assumption that by returning to the earth at the speed of light, you will be "recapturing" time (by adding your own incoming speed to that of light coming from the earth - this contradicts the basic axiom that nothing (with positive mass) can travel faster than the speed of light relative to anything)).

 

[ColJack]

but surely if you shine 2 laser beams at each other, where they meet, they will be "impacting" each other at twice the speed of light.. , each one only traveling at the speed of light.. like 2 trains on a track doing 50mph towards each other.. the impact would be equivalent to crashing a 100mph train into a stationary one ( ok so minus whatever gets lost in inertia etc.. )

 

[ColJack]

my assumptions are no less relavent than the assumptions that all of this theoretical maths / physics is based on..
until I see evidence that time slows as you approach the speed of light then ( and that you rule out ALL other possible reasons for the change ) then I stand by my assumptions..

I know they did a test with 2 atomic clocks, sending one on a flight and keeping on on the ground, but that could simply have been as a result of the decreased gravity at higher altitudes causing the decay rate to alter minutely..
has anyone done a study on the effects of gravity on atomic decay rates? sent a sample on a far out orbit and retrieved it? maybe to the moon and back?
how about dropping it off in space and waiting there for a year until we come back round for it?

 

[EddieM]

no, the fundamental mistake you are making is that your assuming the speed of light can vary.

Totally wrong, the speed of light is constant in a vacuum true, but the speed of light can vary enormously depending on the medium it is travelling through.

 

[empip]

Get the cool photon clock at approx' 2:30 mins into video...

-0-

 

[sooey]

until I see evidence that time slows as you approach the speed of light then

There already is evidence for this. Sat nav satellites have very accurate clocks on board, but they still have to make constant adjustments for the fact that the clocks run slower due to their orbital motion. If the adjustments weren't made the systems would lose accuracy by about 6 or 7 miles a day I believe.

 

[ColJack]

until I see evidence that time slows as you approach the speed of light then

There already is evidence for this. Sat nav satellites have very accurate clocks on board, but they still have to make constant adjustments for the fact that the clocks run slower due to their orbital motion. If the adjustments weren't made the systems would lose accuracy by about 6 or 7 miles a day I believe.

again, prove to me that it's the motion causing the change and not the lack of gravity affecting the clocks..

 

[joinerjohn]

no, the fundamental mistake you are making is that your assuming the speed of light can vary.

Totally wrong, the speed of light is constant in a vacuum true, but the speed of light can vary enormously depending on the medium it is travelling through.

Very true Eddie, for instance if you shine a beam of white light through a prism, it's refracted and split up into it's component colours. This alone proves that light does slow down when travelling through glass. It also proves that different colours of the visible spectrum are slowed down by different rates.
As for two objects travelling away from each other. once they got to just over half the speed of light, relative to each object the other would apparently cease to exist as the light from each object couldn't theoretically catch up with the other.

 

[Lincsbodger]

no, the fundamental mistake you are making is that your assuming the speed of light can vary.

Totally wrong, the speed of light is constant in a vacuum true, but the speed of light can vary enormously depending on the medium it is travelling through.

Very true Eddie, for instance if you shine a beam of white light through a prism, it's refracted and split up into it's component colours. This alone proves that light does slow down when travelling through glass. It also proves that different colours of the visible spectrum are slowed down by different rates.
As for two objects travelling away from each other. once they got to just over half the speed of light, relative to each object the other would apparently cease to exist as the light from each object couldn't theoretically catch up with the other.

The entire argument about photons travelling in matter is interpretable.

In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and the new light interfering with the original light wave to form a delayed wave. In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitations of the matter (quasi-particles such as phonons and excitons) to form a polariton; this polariton has a nonzero effective mass, which means that it cannot travel at c.

Alternatively, photons may be viewed as always traveling at c, even in matter, but they have their phase shifted (delayed or advanced) upon interaction with atomic scatters: this modifies their wavelength and momentum, but not speed. A light wave made up of these photons does travel slower than the speed of light. In this view the photons are "bare", and are scattered and phase shifted, while in the view of the preceding paragraph the photons are "dressed" by their interaction with matter, and move without scattering or phase shifting, but at a lower speed.

Look at it like this - the photons still travel at c, but the delay (and slowing) is created by the information flow across the atom, in absorbing then reemitting the photon. The refractive index is the metric by which information travels through the medium, not the rate it slows light down.

We can all split hairs in physics.............

 

[lifesagasman]

no, the fundamental mistake you are making is that your assuming the speed of light can vary.

Totally wrong, the speed of light is constant in a vacuum true, but the speed of light can vary enormously depending on the medium it is travelling through.

Very true Eddie, for instance if you shine a beam of white light through a prism, it's refracted and split up into it's component colours. This alone proves that light does slow down when travelling through glass. It also proves that different colours of the visible spectrum are slowed down by different rates.
As for two objects travelling away from each other. once they got to just over half the speed of light, relative to each object the other would apparently cease to exist as the light from each object couldn't theoretically catch up with the other.

hopeful theory, but the instantaneous light from object A would simply require time to be visible from object B, dependant on the velocity of B, which explains why light from stars is millions of years old.

 

[Space cat]

Einstein's fundamental postulate (that's physics talk for a leap of faith) states that the laws of physics are the same for all inertial observers, an inertial observer being one moving at constant velocity. The inertial bit is important because, if you're lost in space without a telescope, Newtonian mechanics provides no way to determine whether you are moving or not. Einstein proposed that any experiment you did in your spaceship would yield exactly the same results in a second spaceship moving relative to yours. It's a very reasonable assumption but it has some profound consequences.

So what has the speed of light got to do with this? Let's start here on Earth and measure the speed of sound - because it's easier. You are on a platform 300m long with clocks at each end. A 300m long train comes past, also with clocks at each end. At the back of the train is a cardboard flap which will collide with an identical flap at the end of your platform as the train comes through.

You measure the time it takes the noise to reach the other end of your platform while somebody on the train measures the time it takes to reach the other end of their train. You will get different answers but who's right. Obviously it's you because you weren't moving.

So let's repeat this experiment with two airships high above the clouds without navigation equipment. Once again you get different answers - and once again yours is right because you weren't moving. Or were you??? This conundrum is easily resolved when you realize that sound has a fixed speed through air. If you take your air speeds into account you will both get the same answer.

Now let's repeat the experiment out in space. You can't use sound because it can't travel through a vacuum but light can; so you replace the flaps with a spark gap and away you go. Common sense dictates that you will get different answers so which of you has the right one? Who's moving?

To get out of this, physicists proposed the existence of an aether that filled the whole of space and through which light travelled at a constant speed (unless matter got in its way). So now the race was on to measure the speed of the Earth through this invisible aether. If you look in old physics books you'll find lots of those old experiments.

A simple one used a telescope to observe a distant star. As the Earth orbited the Sun, it would move in opposite directions through the aether and so the focal length of the telescope's objective lens should appear to change. The change they were looking for was ±v/c where v is the Earth's orbital speed. That's about 0.01%; small but detectable. It didn't work. Why? Because the movement of the lens through the aether would alter its refractive index so as to almost cancel the effect being sought. The predicted change was now ±(v/c)^2 or about one part in a hundred million!

Every experiment was dogged by the same first-order cancellation problem. It would need a very sensitive instrument to detect such a tiny variation and so we had to wait for the Michelson-Morley interferometer which proved, beyond reasonable doubt that there was no aether. That wasn't the answer physicists wanted but it's what they got. (The idea of an Earth-centred aether was ruled out as preposterous. )

So now we have two spaceships moving relative to one another getting different answers for the speed of light, despite the fact that the speed of light can be calculated from a pair of easily measured physical constants! Einstein provided the solution by throwing away the concept of absolute time. It sounds ridiculous but it does allow all inertial observers to get the same answer for the speed of light.

There is no proof that the theory of relativity is true because experiments can only ever disprove theories but it does make predictions that can be tested and they work. Fast moving unstable particles do live longer than they should and GPS satellites must take account of their orbital velocity or they would be useless.

 

[sooey]

Nice one spacey, nice to hear from someone who really knows what they are talking about.
It's now all as clear as mud to me.

 

[Lincsbodger]

until I see evidence that time slows as you approach the speed of light then

There already is evidence for this. Sat nav satellites have very accurate clocks on board, but they still have to make constant adjustments for the fact that the clocks run slower due to their orbital motion. If the adjustments weren't made the systems would lose accuracy by about 6 or 7 miles a day I believe.

again, prove to me that it's the motion causing the change and not the lack of gravity affecting the clocks..

well the theory relating to time dilation from motion was proved by three separate experiments:

* Ives and Stilwell (1938, 1941), “An experimental study of the rate of a moving clock”, in two parts. The stated purpose of these experiments was to verify the time dilation effect, predicted by Lamor-Lorentz ether theory, due to motion through the ether using Einstein's suggestion that Doppler effect in canal rays would provide a suitable experiment. These experiments measured the Doppler shift of the radiation emitted from cathode rays, when viewed from directly in front and from directly behind. The high and low frequencies detected were not the classical values predicted. However , this forum lacks the ability to post the maths to prove it.

Rossi and Hall (1941) compared the population of cosmic-ray-produced muons at the top of a mountain to that observed at sea level. Although the travel time for the muons from the top of the mountain to the base is several muon half-lives, the muon sample at the base was only moderately reduced. This is explained by the time dilation attributed to their high speed relative to the experimenters. That is to say, the muons were decaying about 10 times slower than if they were at rest with respect to the experimenters.

* Hasselkamp, Mondry, and Scharmann (1979) measured the Doppler shift from a source moving at right angles to the line of sight (the transverse Doppler shift. Again, you cant post the maths that proves it on this 19th century forum software.............you also have to realise the proofs for this sort of theory are some fairly advanced maths, it isnt primary school algebra.

 

[EddieM]

no, the fundamental mistake you are making is that your assuming the speed of light can vary.

Totally wrong, the speed of light is constant in a vacuum true, but the speed of light can vary enormously depending on the medium it is travelling through.

Very true Eddie, for instance if you shine a beam of white light through a prism, it's refracted and split up into it's component colours. This alone proves that light does slow down when travelling through glass. It also proves that different colours of the visible spectrum are slowed down by different rates.
As for two objects travelling away from each other. once they got to just over half the speed of light, relative to each object the other would apparently cease to exist as the light from each object couldn't theoretically catch up with the other.

The entire argument about photons travelling in matter is interpretable.

In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and the new light interfering with the original light wave to form a delayed wave. In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitations of the matter (quasi-particles such as phonons and excitons) to form a polariton; this polariton has a nonzero effective mass, which means that it cannot travel at c.

Alternatively, photons may be viewed as always traveling at c, even in matter, but they have their phase shifted (delayed or advanced) upon interaction with atomic scatters: this modifies their wavelength and momentum, but not speed. A light wave made up of these photons does travel slower than the speed of light. In this view the photons are "bare", and are scattered and phase shifted, while in the view of the preceding paragraph the photons are "dressed" by their interaction with matter, and move without scattering or phase shifting, but at a lower speed.

Look at it like this - the photons still travel at c, but the delay (and slowing) is created by the information flow across the atom, in absorbing then reemitting the photon. The refractive index is the metric by which information travels through the medium, not the rate it slows light down.

We can all split hairs in physics.............

Good old wikipedia

 

[Lincsbodger]

A US boffin has effectively put the mockers on Star Trek-style warp speed travel to the stars by warning that interstellar hydrogen gas would become deadly to humans as they approached the speed of light.

Professor William Edelstein of the Johns Hopkins University School of Medicine explained that while interstellar space has just a couple of hydrogen atoms per cubic centimetre, as the crew of the Enterprise hit the gas pedal, a compression effect would greatly increase the number of atoms hitting the spacecraft.

As the spaceship reached 99.999998 per cent of the speed of light, "hydrogen atoms would seem to reach a staggering 7 teraelectron volts", which for the crew "would be like standing in front of the Large Hadron Collider beam".

This is a very bad thing, because humans in the path of this ray would receive a dose of ionising radiation of 10,000 sieverts, and as Bones McCoy would doubtless confirm, the lethal dose is 6 sieverts.

The result? Death in one second.

The spacecraft's structure would do little to mitigate the effects of the killer hydrogen. Edelstein "calculates that a 10-centimetre-thick layer of aluminium would absorb less than 1 per cent of the energy", and the intense doses of radiation would damage the ship's structure and fry its electronics.

Edelstein grimly concluded: "Hydrogen atoms are unavoidable space mines."

The professor presented his killer calculations to an American Physical Society meeting in Washington DC on Saturday.