# Tag Info

37

I do disagree with the other answers, not on the result, but on the reason. You don't need to go faster than the speed of light to pass through multiple stars in a few seconds. Putting aside the problems of accelerating to a high enough speed in a human lifetime without being crushed by G forces, storing enough fuel for that (what would you use as fuel? ...

32

Does this logic make sense? Has anyone thought of this before? Yes, it's been considered. In the literature it's known as the "incentive trap". There are a couple of academic papers on it, notably Andrew Kennedy's 2006 Interstellar Travel - The Wait Calculation and the Incentive Trap of Progress and René Heller's Relativistic generalization of the ...

22

The expression $v_e = \sqrt{\frac{2Vq}{m}}$ is a non-relativistic approximation. This is quite valid when the exhaust velocity is small compared to the speed of light, which is the case for ion thrusters made to date (exhaust velocity is on the order of $10^{-4}c$). A more precise expression is $${v_e}^2\left(1+\frac{2Vq}{mc^2}\right) = \frac{2Vq}m$$ No ...

15

Not on macroscopic scale. The Special Relativity theory is fairly well understood and says it's impossible for any objects that possess rest mass, period. The closer you get to speed of light the more energy you need to accelerate, additional energy gets increasingly converted towards mass instead of velocity, so to actually reach it you would need infinite ...

6

Matter cannot move faster than the speed of light in vacuum. Nothing you try to come up with is changing that. (If you do come up with a peer-reviewable proof that it's possible you're in for a Nobel prize.)

6

The important thing to note here is that to say "it takes 8-9 years" doesn't make sense without specifying who it applies to. When relativistic effects start to apply, it's not the same in all reference frames. Let's take your Proxima Centauri example. At half the speed of light, the spacecraft reaches Proxima Centauri in 8.5 years, and if it immediately ...

5

MIT made a little demo game, called A Slower Speed of Light, which attempts to show what would happen as you reach the speed of light by slowing the speed of light in the game. Watch the Youtube trailer to see the relativistic effects, or download the game from MIT's game lab. This game purely shows how visual problems appear very quickly - red- and blue-...

5

Your equation is non-relativistic, and hence only works for small numbers. What happens at relativistic speeds is that, from our point of view, an object will shrink in length, increase its mass, and time will run slower on it. As it approaches light speed, its length will approach zero, its mass will approach infinity, and time will approach stasis. You ...

4

It helps to suppose that you're flying your ship somewhere closer to a galactic nucleus than we are. Sure, the nearest star to us (after the Sun) is several light years away, but if you get within a few light-years of the center of the Milky Way, the average distance between stars is less than 0.02 light year (1/250th of what other answers are taking as the ...

4

Nothing with mass can move at the speed of light. A massless particle (such as a photon) moving at the speed of light experiences no duration (also known as proper time) at all. As an illustration of this, when we observed that neutrinos can change flavour in transit, we could deduce that they must have mass (and so travel below the speed of light) because ...

3

We can't talk about travel at the speed of light, because the length contraction goes to zero for the travelers and their time dilation goes to infinity. It would take infinite energy to go that fast. Instead, let's assume our craft reaches 87% of the speed of light on the way to the Alpha Centauri system. From the perspective of the travelers, the trip is ...

3

I think you've misunderstood something; there's no generally accepted model for light-speed-or-faster travel, and so there's no generally accepted model for the passage of time in such a mode. There is a well-known time dilation effect for speeds near, but below, the speed of light ("relativistic speeds"); a complete explanation is both very long and beyond ...

3

The section "How Much Fuel is Needed" of this page essentially answers your question $$M/m = \gamma (1 + v/c) - 1$$ Here $m$ is the mass of the rocket, $M$ the mass of the fuel (matter/antimatter in equal quantities) $v/c$ is $P/100$ in your terms and $\gamma = 1/\sqrt{1-v^2/c^2}$

2

It's not going to do much at all with a regular sized probe. There are two problems: 1) You can't effectively scale this up due to the incredible acceleration. The bigger it gets the tougher it must be built and thus the lower the acceleration. 2) They're looking to boost a gram or two at 10,000g. Boost a kilogram or two and that drops to 10g. By the ...

2

Yes, via a light-speed U-turn When traveling at speeds close to the speed of light, stars appear to conglomerate into a single blurb in front of a spacecraft (artistic example). When slowing down, those stars will appear to move back to their 'normal' rest positions, and diminish in spectrum (i.e. they will appear to undergo redshift). This means that stars ...

2

The first thing I notice is that the paper first handwaves away the difference between the size of the probe and the size of the replicator. It references the Freitas paper (which is itself pretty handwavey) while failing to mention that the probe required to send the 500t replicator masses ten million tons. The second thing I notice is that the author ...

1

It depends on whether you are approaching or leaving that star. Light undergoes blue shift if the source of light is moving towards the observer (equivalently, if the observer is moving towards the source) and red shift if the observer and source are moving further apart. The equations are not particularly simple for velocities approaching that of light, ...

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