[katieHaylor (OP)]

David says:

If we were able to treat travelling to the stars like a bus journey, say to the nearest star taking 10 minutes, at roughly 4,000,000,000,000 (?)  miles/hour. Would such speeds be possible, and what would the chances be of hitting a stellar object on route?

What do you think?

[jeffreyH]

The speed of light is around 670,616,629 mph. So no, you it isn't possible.

[evan_au]

at roughly 4,000,000,000,000 (?)  miles/hour. Would such speeds be possible?

Unfortunately for fans of Star Trek, Einstein showed in his theory of special relativity that you can't accelerate a massive object from stationary to faster than the speed of light in a vacuum = 6,700,000 miles/hour (= 186,000miles/second or 300,000 km/sec).

Scientists have tried very hard to exceed this limit. The Large Hadron Collider in Switzerland consumes large amounts of electricity to accelerate subatomic particles called protons as fast as possible. They can get them to almost the speed of light (within a few meters per second), but can't get them going faster than the speed of light.

Scientists are looking for some "loophole" in this law that would allow interstellar travel, but none have been demonstrated yet.

travelling to the stars like a bus journey, say to the nearest star taking 10 minutes

Another quirk of the theory of relativity says that the speed of time depends on where you measure it, on the "frame of reference".

By accelerating a spaceship close to the speed of light, the experience of elapsed time would be greatly reduced.
But it takes an enormous amount of energy to do this.

what would the chances be of hitting a stellar object on route?

The space between stars is fairly empty - but even hitting a speck of dust at these "relativistic" speeds would be like setting off an atomic bomb.

At least the scriptwriters on Star Trek they thought of having a "deflector dish" to sweep aside any specks of dust in space, avoiding a premature end to their bold voyages into the unknown.

See: https://en.wikipedia.org/wiki/Speed_of_light#Upper_limit_on_speeds

[Bored chemist]

Jut a thought. Here on Earth, the nearest star is the Sun.
It takes about 8 minutes for light to travel across the space between the to.
So, yes, it's just about possible to travel from Earth to the "nearest star" in under 10 minutes, but it's rather less impressive than you might think.

[jeffreyH]

186000 * 60 * 60 = ?

[Bored chemist]

186000 * 60 * 60 = ?

Pretty much the answer you gave earlier
"around 670,616,629 mph"
Why did you ask?

[unstman]

Excluding the sun, which I should have mentioned was the nearest star, I was thinking of Alpha Centauri, which is 4.22 light years away. So, to cover a distance of 4.22 light years in 10 minutes, this would far, far exceed the speed of light. I may have  my calculations wrong in the initial question? lol  I think you would have to travel at 44,650,000,000,000 km/hour??? or 12.5 Billion km a second. (I think?) lol

[yor_on]

Depends on how you think of it, I presume that it is possible, by local measurements, aka using your wristwatch. And if you decide that you're the sole anchor of the universe, trusting your chronometer then your 'speed' must have been FTL :)

On the other tentacle. It would make for a very egocentric universe in which every chronometer should be its own universe builder. So you would have to come up with something connecting all those 'time lines' and 'speeds' into one coherent universe, agreeable by us all. That's what Einstein succeeded with.

[yor_on]

He did it by presuming c. Then adding time dilation's. Those comes from speeds and mass, as observed by others than yourself.

[evan_au]

If you wanted to travel from Earth to Alpha Centauri, the most comfortable trip for a human would be to accelerate at Earth's normal gravity (1g=10m/s²) until you reached half way, then flip over and decelerate at 1g until you stop at your destination.

Now if we do a "back of the envelope" calculation and apply Newton's theory of motion: v=gt
- where v is the velocity in m/s, g is Earth's gravitational acceleration, and t is time in seconds
- To reach the speed of light (according to Newton's theory) would take almost a year.
- In reality, you will never actually reach the speed of light (as per Einstein's theory, which is more complex to calculate).
- But it does show that after a year of comfortable flight, time will slow down for the astronaut, so the elapsed time will be shorter than for an observer on the Earth.
- To the astronaut on the spaceship at the journey midpoint, the distance will appear to be less than 4 light-years (another quirk of relativity), so it will seem to her that the spaceship has not exceeded the speed of light.

The gains are not that great for a 4 light-year journey, as you spend the first and last year getting near relativistic speeds.
But for a journey to the center of the Milky Way Galaxy (25,000 light-years), most of the journey is taken at relativistic speeds.

Of course, we have no method of powering or accelerating a spaceship at 1g for a year, let alone decelerating it at the end of the journey. For a rocket, you would need to carry a lot of reaction mass - even a sizeable antimatter battery doesn't have enough energy for this.

[evan_au]

The Lorentz factor appears in many places in Einstein's theory of special relativity: SQRT(1-v²/c²)
It affects all the fundamental units of time, length and mass.

It starts to become noticeable at about 10% of the speed of light, when these fundamental units are changed by about 1%.

So an astronaut would start noticing the effects of relativity after accelerating for 1 or 2 months at 1g.

[yor_on]

Yes Evan, forgot to add length contractions to it. The 'speeding observer' if I may say so, would find the universe contracting in the direction of motion. So then it comes down to what he will use for defining a distance. Using the measurements he made before starting to accelerate will give a 'FTL effect' according to his chronometer, while using the distance measured at different times accelerating always will give him under 'c'.

Although practically speaking I suspect it should be a really big headache measuring distances while accelerating relativistically. It's best done theoretically I think :)

[unstman]

There is another major issue in traveling in space at speeds equal to or greater than the speed of light, this being time variations, depending on distance.

e.g. If you could communicate to another person 5 light years away, as if it was in real time, and you said you would see them in 10 minutes...........traveling at the speed of light or greater, would the 10 minutes be increased in respect to time outwith the spacecraft, presuming 10 minutes would be 10 minutes as far as the traveler was concerned?

How much time would have elapsed as far as the person being at a distance of 5 light years?

Would the meaning ' See you in x minutes (or any other time reference) ' become redundant in meaning?   

[yor_on]

Well, they would most probably be dead by those ten minutes :)
Time is a local constant, not a 'universal'.

It's just as 'c' in that it's locally the same, no matter what you do, but when compared to other 'frames of reference' becomes questionable as a 'universal golden standard'. And that's more of a question of what we mean by a 'universal standard' than about what our experiments tells us.

[saspinski]

Considering that the relevant time is that measured by the traveller, it is theoreticaly possible to reach distant stars in minutes. But the acceleration would be so great that any material would be crushed, including of course any living organism. And imagine the amount of fuel to keep accelerating along trillions of km.