Faster than light travel

[theridane]

At high enough speeds (lorentz factor of some crazy big number) all the starlight would redshift into extremely low frequency radio waves and would become impractical to detect (huge antennas). On the ship's fore it would blueshift into hard gamma, which is detectable alright, but also erosive to the chemical bonds of the sensor array (and the ship's hull, and the flesh of everyone inside, ...) and very hard to shield against.

 

[csmyth3025]

At what fraction of c would a hypothetical spaceship be limited in order to avoid hard gamma ray overexposure? Is starlight from local stars or from the Andromeda galaxy a concern or is just blue-shifted CMB the limiting factor?

Of course there's also the possibility of running into micro-meteorites or grains of dust. How prevalent are these sort of things in interstellar and intergalactic space? Is this something we just don't know yet?

Chris

 

[theridane]

At some 0.999999999c (9 nines) white light (540 THz, center of our visible spectrum) becomes gamma (above 10^19 Hz). CMB is less of an issue, as it's both weaker and of lower frequency than starlight (it would be five orders of magnitude below gamma at this speed).

Interstellar matter, however, would get nasty much sooner than that. It doesn't really matter how dense the void is, as even 1 proton per cubic km would be enough to ensure several collisions per second (a 10-meter cross-section ship going 0.999999999c plows through 23 km³ every second, so it's bound to get hit a lot).

A single proton impacting a ship's erosion shield at 0.999999999c releases an energy of roughly 75 mJ - not that much, but considering we're talking about a single proton... that much energy concentrated in a small area like that can easily knock a couple dozen atoms off the erosion shield. A day or two at this rate, and the bow starts to get all ugly.

Note that real interstellar medium is much, much more dense than this - several particles per cubic meter (several billion per cubic km). At these speeds it might even work like aerobraking

 

[csmyth3025]

Thanks Theridane. It looks like we're stuck with the solar system for now - at least until someone invents the warp drive.

That's sort of like the Pilgrims in 1620 saying: "It looks like we're stuck with Massachusetts for now - at least until someone invents the interstate highway system."

Chris

 

[darkmatter4brains]

I think the idea that it is the increase in mass that makes achieving lightspeed impossible is one of those "teachers lie to you" moments - to avoid having to explain something more complicated.This is the easies to make and can form a sort of engine that allows you to travel as fast or faster then light and you can stear effectively as well.

Well, I never had a teacher "lie" to me about that , nor would I say I have had them lie to me in general, but I would say they ... hmmmm ... withhold truths

Like they teach you the charge of an electron is 1.6*10^-19, only to find out later in Quantum Field Theory that this probably isn't the true charge, but rather an effective charge due to vacuum polarization "screening"!

But, don't worry, they are telling you the truth about relativistic mass. And, you can never go as fast, or faster, than the speed of light