>>Hi Hilmar,
>>
>>One more question about which I've wondered. Can matter be accelerated to near the speed of light in the vacuum of space? Assume for proposes of the question, that in a vacuum there would be no resistance to the matter or any other thing that acted upon the matter like gravity, other than the thrust of the rocket engine. Common sense would indicate that a steadily applied force, like in a rocket's thrusters, would over time accelerate the matter to near light speeds or beyond.
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>Near the speed of light, yes, that could be possible in theory. Beyond, no. While getting closer and closer to the speed of light, the mass would increase beyond bounds.
>
>BTW, an electron or a proton can also be considered "matter", so this actually does happen in practice, too. It is for larger chunks of matter that a practical means has not be found yet.
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>Particles like photons always travel at the speed of light - they are said to have "no rest mass". Photons apparently can't travel at a lower speed.

Hilmar, it should be mentioned that the "speed of light" is a constant in a specific medium. In a vacuum it is 186,000 miles per second. The speed of light changes in matter depending upon the index of refraction of the matter. Light can be slowed down below 186,000 miles per second in denser mediums.