# Would we as humans ever be able to travel close to the speed of light?

1. Dec 7, 2009

### zeromodz

I mean how would we ever do it in the first place? What rockets or propulsion units would we use?

2. Dec 7, 2009

### mgb_phys

It doesn't affect measurements you make in your own reference frame.
You wouldn't notice getting shorter, more massive, slower - only an outside observer would.
That's rather the whole point of relativity.

3. Dec 7, 2009

### cfrogue

The SR acceleration equations provide a different and impossible answer.

How much fuel is this? The next chart shows the amount of fuel needed (M) for every kilogramme of payload (m=1 kg).

d Not stopping, sailing past: M
4.3 ly Nearest star 10 kg
27 ly Vega 57 kg
30,000 ly Center of our galaxy 62 tonnes
2,000,000 ly Andromeda galaxy 4,100 tonnes
http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken]

Last edited by a moderator: May 4, 2017
4. Dec 7, 2009

### DaveC426913

Well, it's untold centuries in the future, so the technology we'll use is going to be even weirder than anything we could dream of.

Ask a roman centurion how we will power our hybrid cars in the 21st century. (What's a hybrid car? What's a car?)

5. Dec 7, 2009

### atyy

But the earth is already travelling at 0.99999999999c , so we are travelling close to the speed of light.

6. Dec 7, 2009

### DaveC426913

Since there are no constraints on imagining how we do it, I would guess that, if/when we manage to do this, it will be by
a] not having to bring our fuel with us
b] using something more efficient than "primitive" total conversion of mass to energy.

7. Dec 7, 2009

### cfrogue

I vote for the no fuel option and pick up random particles in space, ....

lots of them.

8. Dec 7, 2009

### cfrogue

How silly of me.

Atyy already has this figured out.

We start out at 0.99999999999c and we do not need to worry about all this.

Sometimes, the answer can be so simple.

9. Dec 7, 2009

### DaveC426913

OK, all seriousness aside, I'm pretty sure the point of pushing c is to get some distance from Earth.

10. Dec 7, 2009

### Matterwave

Only problem with that is the interstellar medium is oh so sparse...you'd need a catching tool on the order of Astronomical units across just to get a few particles.

The interstellar medium is a much better vacuum than any vacuum we've ever been able to create on Earth.

I suppose you could just boost off each star system tho. Aim for one star system at a time, and bring enough fuel for ~10 Light-years of travel.

11. Dec 7, 2009

### cfrogue

Fine then,.

I say drive by planets and whatever else and suck their mass.

I note I can buy the latest vacuum cleaners on TV and they are guaranteed..

12. Dec 7, 2009

### atyy

mgb-phys and I answered when the original question was: would travelling near the speed of light Lorentz contract our organs and kill us?

13. Dec 7, 2009

### Matterwave

In your own reference frame, nothing changes. You would see the universe around you contract though...that would be quite weird! =P

14. Dec 7, 2009

### cfrogue

You failed to consider the acceleration to get you there.

15. Dec 7, 2009

### DaveC426913

When was that the original question?

16. Dec 7, 2009

### cfrogue

The born thread shows our organs would expand during acceleration.

17. Dec 7, 2009

### DaveC426913

What??

18. Dec 7, 2009

### ideasrule

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

Orion spacecraft, which are actually possible to build today, can achieve 8-10% the speed of light using hydrogen bombs and 50-80% the speed of light using matter-antimatter annihilation. If it's possible to store antimatter, relativistic space travel is certainly possible.

BTW, Dave, did you just say "all seriousness aside"?

19. Dec 7, 2009

### cfrogue

???
the born thread recently shows during acceleration, all expands in the accelerasting frame.

20. Dec 7, 2009

### atyy

Oh, I don't know. Maybe I was dreaming, but mgb_phys's answer makes much more sense if he also had the same dream. Anyway, it doesn't matter.