# Could You Avoid Objects Traveling at Near Speed of Light?

## Main Question or Discussion Point

If we suppose that you could travel at near light speed through space, then would there be a problem with bumping into things?

Could you avoid "stuff" in space, such as asteroids, planets, etc. (down to microscopic stuff like particles floating around)?

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Drakkith
Staff Emeritus
Not very easily. At high velocities approaching c, even dust starts to become extremely hazardous. Depending on how fast you are going you may or may not have any way to see what you're travelling towards. When objects are approaching you at near the speed of light, you start to lose the ability to detect them at significant ranges unless they are brightly illuminated or sending out some EM signal. Using something like RADAR to bounce a signal off of them becomes near useless, as the return signal is barely traveling faster than the object it bounced off of.

Not very easily. At high velocities approaching c, even dust starts to become extremely hazardous. Depending on how fast you are going you may or may not have any way to see what you're travelling towards. When objects are approaching you at near the speed of light, you start to lose the ability to detect them at significant ranges unless they are brightly illuminated or sending out some EM signal. Using something like RADAR to bounce a signal off of them becomes near useless, as the return signal is barely traveling faster than the object it bounced off of.
Wouldn't the reflected RADAR signal travel along with the object? Or are we assuming the object is traveling only at a percentage of the speed of light?

Drakkith
Staff Emeritus
Wouldn't the reflected RADAR signal travel along with the object? Or are we assuming the object is traveling only at a percentage of the speed of light?
Well, you in your ship are the one who accelerated to near c. But from your frame, everything in front of you appears to be approaching at near c. So if you send out your radar signal, once it reflects off of the object it barely manages to reach you before the object does.

Well, you in your ship are the one who accelerated to near c. But from your frame, everything in front of you appears to be approaching at near c. So if you send out your radar signal, once it reflects off of the object it barely manages to reach you before the object does.
Oh, now I understand. You've aroused a question I've had for quite some time now (as rookie as it may be): If I am theoretically traveling at the speed of light, and I were to send out a radio signal in the same direction I am moving, would its velocity add to the speed of light (2c) at which I am currently moving at?

Drakkith
Staff Emeritus
You can't travel at c, but you can get very close, so let's say you are traveling at 0.99c. The velocity of the light (or radio signal), as measured by you, is 1c. The velocity of the light, as measured by an observer who standing still, is also 1c. This occurs because of several different effects having to do with relative motion at high velocities, specifically time dilation and length contraction. The Relativity forum should have plenty of posts about these effects. You can either do a search for the threads or start a new one yourself if you can't find one.

Khashishi
Space is very nearly empty, so your chances of hitting something are pretty small. It's probably a good idea to map out your trajectory to avoid any particularly dense regions, but then just hope you don't run into some stray asteroid.

DHF
I would work on the assumption that if your hypothetical crew has the technical know how and resources to travel at near the speed of light, they would also have some method of deflection. Traveling at such speeds would require a level of engineering hundreds of years ahead of our own, perhaps thousands. a Technology like near light travel would not develop in a vacuum so the ship would have access to some manner of shields. One possible system I read about involved the ship spraying a mist of water ahead of the ship. Any dust or small debris would impact the water molecules and their kinetic energy would be absorbed or deflected by the mist.

Not very easily. At high velocities approaching c, even dust starts to become extremely hazardous. Depending on how fast you are going you may or may not have any way to see what you're travelling towards. When objects are approaching you at near the speed of light, you start to lose the ability to detect them at significant ranges unless they are brightly illuminated or sending out some EM signal. Using something like RADAR to bounce a signal off of them becomes near useless, as the return signal is barely traveling faster than the object it bounced off of.
Very interesting. By "EM," do you mean electromagnetic? How fast could that signal travel (say compared to RADAR that you mentioned)? Non-science major here. :)

One thought I had would be what if you mapped out all the "stuff" in front of you beforehand and plotted a course based on that mapping? Would that safely get you through space at high speeds? Or would mapping it all out be too tough or impossible?

Space is very nearly empty, so your chances of hitting something are pretty small. It's probably a good idea to map out your trajectory to avoid any particularly dense regions, but then just hope you don't run into some stray asteroid.
But what of even dust particles as Drakkith mentioned? Wouldn't those be like a super fast bullet coming at you (or rather you going to it, lol)?

I would work on the assumption that if your hypothetical crew has the technical know how and resources to travel at near the speed of light, they would also have some method of deflection. Traveling at such speeds would require a level of engineering hundreds of years ahead of our own, perhaps thousands. a Technology like near light travel would not develop in a vacuum so the ship would have access to some manner of shields. One possible system I read about involved the ship spraying a mist of water ahead of the ship. Any dust or small debris would impact the water molecules and their kinetic energy would be absorbed or deflected by the mist.
That's an interesting point! Hadn't thought about deflection and shield technology. I'm guessing to make things less hazardous, they'd probably send a machine/auto-piloted craft out first to see how things worked out before attempting such a high-speed flight themselves.

Drakkith
Staff Emeritus