# Thread: how long would it take to travel a light-year?

1. ## how long would it take to travel a light-year?

I'm not so keen on the calculations needed, but with current technology, how long would a light-year-long trip take? 1500 years? 200?

2. Depends on how fast you're going. If you're travelling at light speed, 1 year, by definition.

3. Figure it out yourself.
Assuming you're undergoing constant acceleration, the formula is s=ut+a/2*t^2 .
Let's make a couple of assumptions:
You're undergoing constant acceleration of 10m/s (gravity on Earth, more or less (well, more actually)).
Half way there, you're going to turn around and undergo constant deceleration of 10m/s. This way you'll have zero speed when you get there.

So: for the first half lightyear, s (distance) = (a/2) * t^2 = 5 t^2.
So when you know s in meters (c=299792458m/s), divide by 5, take the square root and there's your time in seconds. There's half the journey; double it for the whole one.

None of this takes time dilation into account, of course.

4. I did a bit of a calculation and came up with this, I hope I got it right

Light travels 9,454,254,955,488 Km per year.

Spacecraft travels at around 50,000 Km per hour 438,000,000 Km per year

Just over 21,585 years to cover the distance.

Here's some refs. for a bit of thought.

240,000 miles - Distance from Earth to Moon

93,500,000 miles - Distance from Earth to sun

3,695,000,000 miles - Distance to Pluto at its most distant point

19,000,000,000,000,000 (19 quadrillion) miles (3,200 light years) - Approximate distance to nearest black hole candidate A0620-00

5. See this is why I'm majoring in English.
Seriously, there's a vague awareness of anything as far as my left brain is concerned.
That and I have no effort.. INSTA-PHYSICS!
I guess I shouldn' hang out in SCIforums then, eh?

6. you should stay, this place seems cool if you believe that you cant accelerate past the speed of light then you can go up to it but not beyond it. time dilation is when as you approach the speed of light time slows down for you. if someone was watching your craft leave they would see it going infinitely slow and stretch out then it would seem to "snap" and seem to accelerate all at once. from inside the ship you would see everything else going infinitely slow also.if you acheived the speed of light or beyond it then even light would seem to stretch out and slow down. if you ask me i say damn the acceleration and just use some sort of ftl drive or some sort of "insto-travel" device. this is how I understand it. i may be wrong but their are many theories as to what would really happen as you started to accelerate to and past teh speed of light.

7. ## Acerbus

As I understand it, one of the things that happens when mass approaches light speed is that it [Mass] approaches infinity, hence it would take infinte energy to accelerate any mass to the speed of light. I think that is one of the reasons why light speed is seen as the limit (i.e. never go faster than the speed of light).

8. ## correction

Originally Posted by Alpha
Depends on how fast you're going. If you're travelling at light speed, 1 year, by definition.
You are wrong sir as a light year isnt a measurment of time but distance if you travelled at the speed of light you could in theory do it a lot quicker as a year travelling at light speed would mean 100 years pass on earth strange as it is while you travel forward faster you age slower so in the theory faster than the spead of light means your going back in time yet although your going backwards your self earth doesnt as its time line continues at its own speed so you could get younger by traveling a 2 x the speed of light yet earth will still age luck of it is tho an object that had mass could never reach that speed by it moving its self it would just be atomised if it did but they say that we can travel 10 faster than the speed of light in warp but then we aint actually moving time and space is moved instead so we aint travelling at 10x the speed of light space and time its self is if they ever manage to create a warp engine which in theory is possible in the future but would be safe travel to as we just sit still and the destionation comes to us if im lucky I might even get to see it in my time the way technology is today they have the idea for a warp ship just not how to create mass amounts of negative energy to create a warp bubble

9. Originally Posted by kevdunne3
You are wrong sir as a light year isnt a measurment of time but distance if you travelled at the speed of light you could in theory do it a lot quicker as a year travelling at light speed would mean 100 years pass on earth strange as it is while you travel forward faster you age slower so in the theory faster than the spead of light means your going back in time yet although your going backwards your self earth doesnt as its time line continues at its own speed so you could get younger by traveling a 2 x the speed of light yet earth will still age luck of it is tho an object that had mass could never reach that speed by it moving its self it would just be atomised if it did but they say that we can travel 10 faster than the speed of light in warp but then we aint actually moving time and space is moved instead so we aint travelling at 10x the speed of light space and time its self is if they ever manage to create a warp engine which in theory is possible in the future but would be safe travel to as we just sit still and the destionation comes to us if im lucky I might even get to see it in my time the way technology is today they have the idea for a warp ship just not how to create mass amounts of negative energy to create a warp bubble
Just a few points.
1. This thread is 12 years old.
2. learn to use punctuation.
3. Everything you've written is incorrect.

10. You see this all looks long like we would all be dead before we got there ha ha but in theory the distance isnt the issue its the time it takes to get there if you travel at the speed of light time stands still meaning why you travel a light year in possibly a few weeks everyone on earth you know would be gone I just love the thought that the quicker you travel the less you age and if uou travel faster than light speed 1x faster for each light year you travel you go back a year in time too yet on earth time has gone forward another 100 years you see going back in time is impossible its just your travelling that fast that time cant keep up for example we measure speed by distance per hour mph kph yet time at that speed cant be measured I love the thought of space but to be honest if we were ment to take to the stars why is it so far just to another planet let alone another star

11. None of what I say is correct and light years are not a measurment of time like our years but of distance and after all that I was just trying to help you no need to be snotty

12. Only an object of mass cant travel at the speed of light but space and time its self can move faster

13. The traveling isnt a problem but humans will never be able to move in any cind of ship at or beyond the speed of light at that speed wed be atomised but in theory we can travel at warp wich could be 10 times the speed of light but not actually have to move so not breaking the laws of realativity in theory its like taking a short cut without leaving the start wich would make for a great holiday

14. Your sentences are unique.

15. Originally Posted by kevdunne3
The traveling isnt a problem but humans will never be able to move in any cind of ship at or beyond the speed of light at that speed wed be atomised but in theory we can travel at warp wich could be 10 times the speed of light but not actually have to move so not breaking the laws of realativity in theory its like taking a short cut without leaving the start wich would make for a great holiday

In reality all that space travel is a bunch of BS. On paper you can accelerate decelerate , but at the end you can wipe yourself with the exercise, and go no were.

16. Originally Posted by arauca
In reality all that space travel is a bunch of BS. On paper you can accelerate decelerate , but at the end you can wipe yourself with the exercise, and go no were.
you wipe yourself and go no were. He is a young kid, probably from UK, and might just as well be part of ESA astronaut team someday.

17. Originally Posted by spankyface
I'm not so keen on the calculations needed, but with current technology, how long would a light-year-long trip take? 1500 years? 200?
I don't know if the information used in these calculations is still valid, but 20 years ago sci-fi writers were assuming that there might be habitable planets within about 10 LY. Based upon:
• 1. the maximum acceleration that a human body can tolerate for a long period of time
• 2. (surely unconscious with the ship running itself),
• 3. and accounting for the fact that for the entire second half of the trip the ship has to decelerate so it doesn't just crash into the planet,
• 4. and assuming that by then we'll be able to provide the power for that level of acceleration
• 5. not to mention the fuel to last that long
They figured that it would be a 40-year trip. So it was just barely feasible that one crew that starts out in their 20s would be able to explore the planet and come back. The suspended animation would help slow down aging.

I have no idea what that translates to for a one-LY trip. Obviously the first light-year is the slowest! I can do that math but I don't feel like it today. One of you youngsters can surely do it faster and more accurately. You might even know how far it is to the nearest possibly habitable planet. I'm sure it's farther than we thought in 1993.

18. Fraggle, those sci-fi writers clearly didn't know what they were writing about.

A 10LY journey with acceleration to the mid-point of 1g and then -1g thereafter would take c.12 years to get to the destination (as measured from Earth) and only c.5 years as measured on board the ship.
And max speed achieved would be 0.987c - quite an achievement.

If you're thinking of the max that humans can tolerate, then 3g would be uncomfortable if also moving around. This would result in trip of 10.6 years (earth time) and 2.3 years ship time, and max speed of 0.998c!

At 5g (e.g. assuming occupants in hibernation etc) then it's 10.4 years earth time, and 1.5 ship time. With max speed 0.999c at the mid-point.

I think, perhaps, the acceleration those writers may have been referring to was the max that they could foresee ships performing?
A 1g acceleration for 12 years would take some considerable leap in tech and fuel performance - e.g. anti-matter and more. Even then it may simply not be feasible.

If the ship accelerates at 0.1g then it would take 22 years from earth point of view and 19 years from on-board pov (max speed 0.75c).

If the ship accelerates at 0.01g then it lengthens to 63 years (62 on-board), and max speed of 0.3c etc.

Even hard-SF writers would have to get this sort of data correct to be taken seriously.
They'd also have to explain why the ship would bother accelerating at 5g rather than 1g if it only shaves c.2 years off each leg of the trip.

19. We have no idea what technology the real powers that run earth has. The world thinks nukes are the best weapons we have although they where made in 1940's.

You telling me after all this time, no better techs exist. Of course they do

But they are not telling us, so the question of the op is not something the lay person can answer.

20. Originally Posted by andy1033
We have no idea what technology the real powers that run earth has. The world thinks nukes are the best weapons we have although they where made in 1940's.

You telling me after all this time, no better techs exist. Of course they do

But they are not telling us, so the question of the op is not something the lay person can answer.
Nutcase.

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