Would it be a bad idea to travel the speed of light?

[willwolvescry]

Let's face it. Everyone wants to travel the speed of light even if its just to get to the moon in seconds but let's think about this. We do know right now Light speed travel is impossible for manned flights currently and at best we can make particles achieve light speed but I see some major problems. First off the most obvious to me is navigation. When we finally do achieve manned light speed travel how do we know where we are going or more importantly where we are? Currently what we use to navigate wont work for light travel. Most of our navigation is visual and we wouldn't be able to see any visual cues since light wouldn't be able to reach our eyes fast enough. Any auditory cues would also be useless for the same reason. Felt cues may work but by the time we receive them and react it may be too late. Let's also think about getting out of light speed. If it takes a long time to return to a safer speed wouldn't it seem rather pointless well with the exception of long distance travel. Finally what would happen if the worst were to happen? What would happen if you crashed into an object at light speed? Would you be absorbed or would you be vaporized?

[SargeRho]

First of, it's not possible to travel *at* the speed of light. It's not advisable to do either, since at that kind of speeds, a grain of dust hits with the force of a large nuclear device.

At something like 99.9% the speed of light, I think you can travel to the edge of the Galaxy in a week as seen from your point of view, but by the time you arrive there might not be a galaxy left the edge of which you were traveling to.

[K^2]

This is the sort of thing that happens when two nuclei collide at near-light speed. Collisions with absolutely anything, down to space dust, is going to be really, really bad.

Navigation you can work around. Combination of inertial navigation and some other cues, like signals from pulsars, would get you to the right general location, and you can slow down well ahead of your destination to make corrections. Compared to all other issues, this is category of engineering problems. They might be tricky, but we have means of solving them. Actually accelerating to light speed and protecting ship from impacts are the more fundamental problems of near-light speed travel.

[Themohawkninja]

First of, it's not possible to travel *at* the speed of light. It's not advisable to do either, since at that kind of speeds, a grain of dust hits with the force of a large nuclear device.

At something like 99.9% the speed of light, I think you can travel to the edge of the Galaxy in a week as seen from your point of view, but by the time you arrive there might not be a galaxy left the edge of which you were traveling to.

75,000 years at most isn't going to do much to the galaxy. It's still a few billion until we "collide" with the Andromeda galaxy (the quotations are just because the term 'colliding' isn't really an apt way of describing it).

[Themohawkninja]

Navigation you can work around.

What about avoiding stars (or an other large body for that matter)? To the best of my knowledge, we can only determine a star's distance to within a few percent, which is quite a large uncertainty as far as navigation goes.

And that is only the things we can easily see.

[SargeRho]

75,000 years at most isn't going to do much to the galaxy. It's still a few billion until we "collide" with the Andromeda galaxy (the quotations are just because the term 'colliding' isn't really an apt way of describing it).

You forgot relativity. A week passes for you, but millions if not billions of years may pass in "normal" time.

[brooklyn666]

That depends entirely on how you plan on achieving that speed. If you plan on using an artificial wormhole or some sort of Alcubierre Drive, you avoid all of the consequences mentioned above.

[K^2]

What about avoiding stars (or an other large body for that matter)? To the best of my knowledge, we can only determine a star's distance to within a few percent, which is quite a large uncertainty as far as navigation goes.

Number of stars and other dense objects is so low, that you might as well just take your chances. Navigate far from the stars you know to the best of your ability, and take the chance with rest.

some sort of Alcubierre Drive, you avoid all of the consequences mentioned above.

No, you don't. Matter in the path of Warp Drive is still a problem. And we are talking about sub-light travel, not FTL.

[DaveofDefeat]

Full power to the deflector shields!

[Seret]

Most of our navigation is visual and we wouldn't be able to see any visual cues since light wouldn't be able to reach our eyes fast enough. Any auditory cues would also be useless for the same reason. Felt cues may work but by the time we receive them and react it may be too late.

Um, auditory?

Are you talking about difficulties with the ship displaying information to the crew? That wouldn't be a problem at all, since they're not moving relative to one another.

Edited December 30, 2013 by Seret

[Ravenchant]

You forgot relativity. A week passes for you, but millions if not billions of years may pass in "normal" time.

Nope. At 99,9% lightspeed, the Lorentz factor is still only about 22,4, which means that for each "week" passing for the people on the ship, the stationary universe around them ages about half a year. If you want to get to the edge of the galaxy, you'll have to go faster than that. At 99,9999% c it would just about be achievable within a human lifetime.

[willwolvescry]

Um, auditory?

Are you talking about difficulties with the ship displaying information to the crew? That wouldn't be a problem at all, since they're not moving relative to one another.

[Seret]

Relative positioning would still be a problem since light will just like sound does when traveling mach speed.

Nope, the speed of light is the same for everybody regardless of how they move. Light and sound do not behave the same.Sound itself is only affected if you're moving at a different speed from the medium that it's travelling through, which you wouldn't be. Within an aircraft moving at supersonic speeds sounds are perfectly normal. If they weren't how would the cabin crew of the Concorde have served you your champagne?

Edited December 30, 2013 by Seret

[ZetaX]

On the Lorentz factor and special relativity, there is a neat way to very easily calculate some things:

You don't need the Lorentz factor to do some types of computations at all. The Lorentz factors cancel when calculating flight time from the space ships own frame of reference, thus everything behaves like in the classical scenario as long as no interaction with other objects is considered. Therefore, investing 4 times as much energy into velocity will get you there exactly two times as fast, i.e. in half the time, from your point of view.

And if you travel to anywhere outside your current solar system in comfortable flight times (own frame again) of at most months, then your speed relative to the stars is rather close to c, letting you expect a year per lightyear to happen in the frame of the stars/the galaxy.

[Themohawkninja]

You forgot relativity. A week passes for you, but millions if not billions of years may pass in "normal" time.

Right, but if you are traveling across the galaxy at near the speed of light, it will take at most 75,000 years of "normal" time to do it.

[architeuthis]

The impact energy of a single mote of space dust with relative velocity of 1c isn't so bad. A mote of space dust masses about the same as a bacterium; it would only have an kinetic energy of about 10J. Over time this would sandblast your hull, but otherwise it is not particularly devastating. It also means that the dust exerts a pressure on the hull not unlike aerodynamic drag in an atmosphere; therefore relativistic rockets, if they ever are built, will probably be streamlined, sleek designs.

But there would be some pretty extreme radiation hazards for near-light speed travel. At .99c visible light blueshifts into x-rays, which may not be a big problem if you are in the interstellar void but flying through a solar system at that speed would be a death sentence. Even worse is that interstellar gas and dust particles would have energy comparable to high energy cosmic rays, on the order of 100MeV up to 1-3GeV. In unshielded conditions this would equate to human radiation dosages in the tens- to hundreds of thousands of rems per second, which is similar to conditions inside the core of a nuclear reactor. Some of these particles are charged, so they could in principle be deflected with magnetic shields (of course then the problem would be cohabiting with 20 T magnetic fields). To deal with the neutral particles you would need a many meters thick radiation shield made out of water or titanium. Also our solar system is inside a bubble of abnormally low density interstellar medium. In other areas of our galaxy the radiation hazards might be even more extreme, therefore interstellar travel of the far future will probably have galactic navigation routes passing through low density corridors not unlike the hyperspace trade routes from starwars:)

[brooklyn666]

Number of stars and other dense objects is so low, that you might as well just take your chances. Navigate far from the stars you know to the best of your ability, and take the chance with rest.

No, you don't. Matter in the path of Warp Drive is still a problem. And we are talking about sub-light travel, not FTL.

The title of this thread is "Would it be a bad idea to travel the speed of light?" So how is that not talking about FTL?

[K^2]

It helps to read the opening post, not just the title. Author compares it to particles in an accelerator, so he's obviously talking about very, very close to light speed, yet sub-light.

[brooklyn666]

When we finally do achieve manned light speed travel...

He explicitly stated it right there.

[K^2]

And by light speed, he clearly means near-light speed.

is impossible for manned flights currently and at best we can make particles achieve light speed

You don't need the Lorentz factor to do some types of computations at all. The Lorentz factors cancel when calculating flight time from the space ships own frame of reference, thus everything behaves like in the classical scenario as long as no interaction with other objects is considered. Therefore, investing 4 times as much energy into velocity will get you there exactly two times as fast, i.e. in half the time, from your point of view.

No, actually, it does not. All has to do with the way proper acceleration works. As it turns out, once you are going really, really fast, speeding up gets way easier.

Edited December 30, 2013 by K^2

[brooklyn666]

Since he brings up BOTH FTL and near speed-of-light travel, how about we stop quibbling over minutiae?

[K^2]

Where does he even once mention faster than light?

[brooklyn666]

Ok, clearly you're going to continue on with this, so I'm going to bow out.

[Ravenchant]

For all practical purposes, "light-speed travel" means near or infinitesimally close to the speed of light. Travelling exactly at light-speed is not FTL, photons do it all the time.

It's actually technically possible to go FTL - just not in a vacuum

[maltesh]

The impact energy of a single mote of space dust with relative velocity of 1c isn't so bad. A mote of space dust masses about the same as a bacterium; it would only have an kinetic energy of about 10J. Over time this would sandblast your hull, but otherwise it is not particularly devastating. It also means that the dust exerts a pressure on the hull not unlike aerodynamic drag in an atmosphere; therefore relativistic rockets, if they ever are built, will probably be streamlined, sleek designs.

You cannot use the classical Kinetic Energy formula when calculating kinetic energy for objects moving with relativistic speeds. You either have to plug relativistic mass into the kinetic energy formula, or you have to use the relativistic kinetic energy formula.

Any object with any positive value of rest mass would have infinite kinetic energy if it was moving at 1c.