Lightyear Thought Experiment

[deleted-300380]

A lightyear is the distance light can travel, in a vacuum, over one year ( some 10 trillion km ). It's also how we measure the age of the universe. If a star is 10 lightyears away, we know we're seeing it ten years in the past because it took that long for the light to get here. However, if I were a being that evolved on a planet thats orbit was shorter than Earths, say 250 days, wouldn't my lightyear be less distance? And if that was the yard stick I used to measure the distance between stars or age of the universe, wouldn't I come up with a different answer than we do here on Earth? Wouldn't my age of the universe be way different? That's my question; Is a lightyear standard across the entire universe? From any perspective? On any planet in the universe?

[bfinio]

Hi Haley72,

When we say "one year" on Earth, we mean "one Earth year" which is 365 of our (Earth) days. You're correct that a civilization that evolved on a different planet with a different orbit would have a different definition of "year." So, any other quantities derived from the length of that year (for example, the distance of a light year) would also be different.

In the example you gave, that planet's definition of "light year" would be 250/365 = 0.685, or 68.5%, as long as ours. So, by their definition, that star that's 10 of our light years away would be 10/0.685 = 14.6 of their light years away. However, the actual distance to the star would still be the same - we just have different definitions of how far a "light year" is.

It's just like using two different units of measurement for anything else - like miles and kilometers. Someone in America might say that two cities are 10 miles apart, and someone in Canada might say that two cities are 16 kilometers apart. The actual distance between the cities is the same because 10 miles = 16 kilometers, but the units are different lengths so the numbers are different. In your example the different units are "Earth light years" and "other planet light years." Does that make sense?

[deleted-300380]

That makes total sense. Like the title suggests, it was just a thought experiment. I imagined what would happen in a "First Contact" type of situation. And what would happen when we started comparing notes on what we know about the universe. And I thought: "Would we end up getting in some sort of a tussle because in their minds the universe is way older than WE are saying"? Or "Would they think we're total morons"? (though, in this scenario we did just create a warp drive, so maybe a bad example) Then the question a universal standard popped in my head. Of coarse we would use math to show it's the exact same thing. MATH is the universal standard. Not sure why that didn't occur to me. Not enough sleep I guess. lol

Thank you for the response!

[bfinio]

No problem. If you want to learn more, you should read about how one second is defined - it's based on the vibrations of a specific atom, which is independent of any "astronomical" variables - so it's the same regardless of what planet you're on or what star you're orbiting:

https://www.google.com/search?q=how+is+ ... 8&oe=utf-8

so, if we needed a common unit of time, that would be a place to start.