Near Light Speed Travel Possible After All?

DrStrabismus writes "PhysOrg has a story about research that may indicate that close to light speed travel is possible. From the article: 'New antigravity solution will enable space travel near speed of light by the end of this century, he predicts. On Tuesday, Feb. 14, noted physicist Dr. Franklin Felber will present his new exact solution of Einstein's 90-year-old gravitational field equation to the Space Technology and Applications International Forum (STAIF) in Albuquerque. The solution is the first that accounts for masses moving near the speed of light.'"

Comments

Actual papers...

[QuantumFTL]

For more information, see Dr. Felber's recent works on arXiv.org:

Weak 'Antigravity' Fields in General Relativity
Exact Relativistic 'Antigravity' Propulsion

Personally I'm a bit skeptical about his claims, however energy appears to be conserved. This method uses gravitationally-mediated kinetic energy exchange - this is the same principle that allows gravitational slingshot to work.

Has Slashdot become crackpot central?

[Expert Determination]

The most obvious giveaway is

Felber's research shows that any mass moving faster than 57.7 percent of the speed of light will gravitationally repel other masses lying within a narrow 'antigravity beam' in front of it.

because, of course, no physical phenomenon can operate only for masses travelling above a fixed speed like that because such a phenomenon would violate Lorentz invariance. Therefore he's not actually using Einstein's equations which are fully Lorentz invariant. Note that I'm making weak assumptions here - I'm not even assuming the validity of Einstein's field equations, I'm just saying that this work doesn't follow from the equations he claims it follows from. That means he's made up some new physics, something completely untested, and is therefore a crackpot.

Re:Has Slashdot become crackpot central?

[barawn]

because, of course, no physical phenomenon can operate only for masses travelling above a fixed speed like that because such a phenomenon would violate Lorentz invariance.

No. (For one thing, Cerenkov radiation is a physical phenomenon that operates only for masses travelling above a fixed speed.)

All this is saying is that if you've got an object (say object A) at rest, and another object (say object B) approaching object A at more than 0.577c in object A's reference frame, object A will be pushed forward (away from object B). Obviously if object A and object B are aligned exactly, they'll collide - but if object A is off-axis from object B, it will be "pushed along" with object B.

Since the relative velocity is measured in one object's rest frame, it's Lorentz invariant. (Object B sees object A approaching it at 0.577c, and sees object A pushing object B backwards).

It's very similar to frame dragging, actually. With frame dragging, there is likely a "critical rotational velocity" above which an object near the rotating object will be forced into an orbit. There's probably a "critical rotational velocity" above which an object deflects every incident object away from it.

And as with frame dragging, it likely exists for lower velocities - but the "push" is probably not along the axis of object A's direction, which means it won't "push" the object along.

Re:The subjunctive case

[barawn]

This guy seems to be saying that if you have an anti-gravity machine, you could counteract that.

Nonono: he's saying that a mass travelling near the speed of light creates an "antigravity beam" in front of it. This sounds hokey, but it's not unprecedented - frame dragging is a similar situation where general relativity basically says that a moving body can "push" others nearby. So in this case the near-light-speed object is "dragging" its frame forward. Calling it an "antigravity beam" sounds wacko, but it's probably quite straightforward. It's almost like the objects would be riding the "wake" of the NLS object, caused by the fact that the object is moving faster than space can respond.

He's essentially saying that you can pretty much effortlessly accelerate something to really high velocities with little effort by hitching a ride on a bigger object.

(Where to find a star moving at greater than .577c is another question.)

Re:Make sure you account for everything

[Plunky]

Surely time dilation effects would significantly lessen the amount of air and food that needs to be carried?

Re:WTF?

[LurkerXXX]

Because if you have to accellerate for an entire year to get above the 57% the speed of light he's talking about, there's a lot more time/distance you have to go through where you are likely to run into a piece of sand that is gonna do just nasty things to your spaceship. Once you are above that 57% cuttoff, you have a nice antigravity field clearing your path (according to him).

What if, after you have been accellerating for months, but are still at only 50% the speed of light, you hit a 1 lb chunk of rock/dust/ice that fell off some asteroid...

50% of speed of light = 1.5 x 10^8

1 pound = 0.4536 kg

Kinetic energy = (.5) (mass) (velocity) (velocity)

Kinetic energy = (.5) (.4536 kg) (1.5 x 10^8) (1.5 x 10^8)

Kinetic energy = (5.1 x 10^15)

Ouch.

The energy of the atomic bomb dropped on Hiroshima was only ~ 5.2 x 10^13

Even hitting a piece of sand at half the speed of light is gonna do waaaaaay more than just scratch your paint job. You want to get to get up to speed where you have the antigravity-clearing path for you as soon as possible, because every second going less than that speed is extremely dangerous. (That's if his theory isn't entirely bogus.)

Re:Go fast enough to look like a black hole?

[pammon]

> One thing I have often wondered is if an object moves fast enough, could its relativistic mass become so large that it
> would look like a black hole relative to a laboratory frame?

No.

Re:Make sure you account for everything

[SirBruce]

Sorry, extrans didn't work right the first time...

He's talking about this:

http://math.ucr.edu/home/baez/physics/Relativity/S peedOfLight/Superluminal/superluminal.html

And he's right, in that yes, sometimes things CAN appear to be moving faster than light at first calculation. I don't think it would work exactly as he described with an object coming straight at you, however.

Bruce