Heretik

Yes, I expect so. What a pity that it is SO difficult to directly experiment with these topics. It is fun to think about them, though.

Thanks for that, Spyman. Now, I could be wrong but I suspect that we only have half the equation. When a body(A) is travelling at a very high speed relative to another body(B ), the light it produces is redshifted. Also the light produced by body(B ), obviously also travelling at a very high speed relative to body(A), is also redshifted. When something is producing redshifted light it follows that when receiving light from other sources, the received light should be blueshifted. Therefore the redshifted light produced by (A) should be blueshifted when received by (B ), and the redshifted light produced by (B ) should be blueshifted on receival by (A). That means that the relativistic component of the light received by (A) and (B ) from each other is a big, fat, Zero. This leaves only the Doppler shifted light to explain the red/blue shifts observed. Maybe the observable universe is expanding at a different rate to what we thought.

As soon as you say the word, "accelerate", the scenario is not subject soley to Special Relativity. Special Relatively only pertains to the special case of objects travelling in a straight line at a constant speed. As soon as the speed is altered General Relativity is invoked. Seeing as Brian is the one being accelerated relative to Andy, he is the one to experience time dilation. Both he and Andy on his return agree that Brians clock is slow but the math to figure out by how much is beyond me, i'm afraid.

I'm sorry but you didn't seem to understand my point! If you'll re-read my scenario you'll see that the space craft is, "broadcasting light and other EM radiation from within itself", not reflecting light. In other words it has flood lights and a radio transmitter scattering light and other EM radiation 360 degrees. The light and other EM radiation that it is manufacturing is, according to Einstein's theory of special relativity, running slow compared to the observers who are passing/being passed at .87 the speed of light relative. In fact, at that relative speed all that happens on board the craft is happening at about half speed, according to the observers. This has no effect on the speed of light from anyones point of view. What it does do is slow down the freguency of the light/Em Radiation reaching the observers. That is, a barely visable violet light would be seen as a barely visable dull red. The frequency of this light/EM radiation is further modified, according to the observers, by the Doppler effect. This means that the observers behind the craft see the light/EM radiation as having a lower frequency than the observers in front of the craft. The dull red would become an invisable infra-red to the rear observers and to the observers in front, the dull red would become an invisable ultra-violet. This effect is commonly called redshift and blueshift. If the craft WAS reflecting light produced by the observers, the reflected light would only be subject to the Doppler effect, from the point of view of the observers.

I think we approximately agree with each other...

1st Yeah, I knew I'd get into trouble for putting it that way. Delete "stationary to the Cosmos" and insert " the observers are all stationary to each other and the craft is travelling .87c relative to the observers" 2nd The redshift referred to is because the craft producing the light/EM radiation is travelling at a relativistic speed (.87c) relative to all the observers which would reduce all onboard processes to about half the clock speed experienced by all the observers. The Doppler effect is a seperate effect caused by the observed shortening of the wavelength of transmitted EM radiation if the craft is coming towards an observer or the observed lenghtening of the wavelength if it is going away from the observer. Thanks for that Janus. 1; The speed of light is not in question. From the instant that each individual photon of light leaves the spacecraft and travels the distance from where it left the craft to where the observer happens to be it travels at 186000 miles/sec. 2; I see the terms "Relativistic" and "Doppler" as two completely separate processes, "Relativistic" always resulting in a redshift and "Doppler" resulting in a redshift if going away from the observer and a blueshift if going towards an odserver. It's a great article. Thanks

Consider a spacecraft travelling through the cosmos at a constant high speed, say .87c, and vector. It should be experiencing time dilation to about half normal (stationary) time. Ie, 1 sec to it would be experienced as 2 seconds to all stationary observers regardless of their orientation to the spacecraft. By that I mean regardless whether the observers are behind, beside or ahead of the spacecraft. The craft is broadcasting light and other electro-magnetic radiation from within itself as it is travelling. Because of time dilation this EM radiation would be observed as redshifted by all (stationary to the Cosmos) observers. In addition to this, the fact that it is moving changes the wavelength of the EM radiation that reaches the observers due to the well known Doppler effect. Where the observer is situated will determine how that wavelength is changed. For example, to an observer behind the craft the EM radiation will be redshifted. To an observer in front of the craft the EM radiation will be blueshifted and the observer that is beside the craft for the briefest of moments that the craft is actually beside the observer, he will notice no frequency change. Ok, it will be blueshifted changing to redshifted the instant it goes past. The point here is that to the observer in front, the EM radiation would be redshifted first due to time dilation, then blueshifted because of the Doppler effect. This would cancel out the redshift resulting in no net frequency change. Therefore there should be no observable blueshifts in the the universe. However astronomers do observe some blueshifts. Why is this? Could it be that there is no time dilation due solely to velocity? Or could it be that at a given speed the Doppler effect more than compensates for the time dilation giving a net blueshift. Somebody do the Math!!

The reason that there are time paradoxs with special relativity is that Einstein got it part wrong. Which part? In his parable of the train with the light beam bouncing up and down he mistakenly assumed that inside the train was a separate part of space-time to the outside of the train. In fact it is not separate and the observer in the train will see what the outside observer would see.. ie, the light beam zig zagging between the mirrors in the direction the train is coming from, the zig zags becoming greater as the speed increases. So, no time dilation due to speed. However, due to the tremendous input of energy to accelerate the train to near light speed the mass of the train would increase tremendously to where there would be time dilation due to gravity... a la general relativity. There are no paradoxs involved with general relativity.