## Distance to Time

Discussions on introductory science topics. Ask simple or beginner questions and expect clear and level answers.

### Distance to Time

How do we convert light years (distance) into years (time)? If something is four light years away, how do we say how long it would take to get there? I assume we need to know how fast we are traveling but there must be a basic number that we generally use and I am not finding it. Or do not recognize it when I see it.
vivian maxine
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### Re: Distance to Time

Hi Vivian,

Fun question. Obviously, you already know that a Light Year is a distance. It's how far light can travel in a Year:

1 Light Year in distance:
or
Exactly: 9,460,730,472,580,800 Meters.
or

Vivian wrote:If something is four light years away, how do we say how long it would take to get there?

Depends on your speed and point of view.
If you could travel at Light Speed.. it would take 4 years as measured from home.
If you could travel at Light Speed.. it would take 0 time as measured by your watch.

See clocks and aging slow down with your speed as compared to the Speed of Light Maximum.

If you could travel at about 86% the Speed of Light:

At about 86% the Speed of Light your aging and clocks will slow down to about 50% of normal.

http://www.emc2-explained.info/Dilation-Calc/#.WKhcEzjSMSU

Note: This doesn't consider the time it takes to get going or time to slow down. That is a lot more complicated.

http://convertalot.com/relativistic_star_ship_calculator.html

1 Gravity (1G) of acceleration means you will feel normal weight while always picking up speed. At 2G's you will have twice the weight for the whole trip.

At 5G's you would weight 5 times as much as normal.. so how long do you think you could stand weighing this much? Would not be very comfortable for sure.

Computing the time for speeding up and slowing down:

For 4 Light Years of distance:
At 2G's it would take 4.8 years to go the distance by Earth clocks.
At 2G's it would take 2.2 years to go the distance by your watch.

The nice thing about acceleration/deceleration (2G's) is if you wanted to go real far.. like 25 times further or 100 Light Years distance.. then it would only take about twice as long (5.1 years by your watch). Sadly, your friends back home will be about 100 years older during your 5.1 year trip there.

If your target destination was 200 Light Years away (twice as far).. then by your watch.. it would only take about 5.8 years at 2G's (pack a really big lunch). Back home about 200 years have passed for your 5.8 year trip (so don't forget to turn off the oven before you leave).

(Also, stopping for gas along the way would be a bitch.. lol.)

Hope that helps.

Best wishes,
Dave :^)

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Location: Tucson, Arizona
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### Re: Distance to Time

Hi Vivian,

A correction is needed above as pointed out by my friend Positor.

I wrote: 5,878,625,000,000,000,000 Miles.

It is: 5.878 625 trillion Miles.

https://en.wikipedia.org/wiki/Light-year

or: 5,878,625,000,000 Miles.

I didn't compute it.. I looked it up on Wiki.
The problem was with my eyes. I didn't see the decimal point.
So I thought it said: 5 878 625 Trillion Miles.

Losing my eyesight is just one of many reasons I need to retire soon.

Thanks Positor.

Regards,
Dave :^)

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Posts: 3230
Joined: 08 Sep 2010
Location: Tucson, Arizona
Blog: View Blog (2)

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