[Public domain], via Wikimedia Commons

According to special relativity, how fast does my dog have to go to age the same as me if one calendar year is equal to seven dog years?

Short answer: About 99% of the speed of light

Long answer: “Dog years” is a bit of a made-up thing, just meant to show that dogs have a lifespan about 7x shorter than a human on average. There’s no timey wimey madness there.

No one can say for sure how different species experience time. How would you even begin to devise such an experiment? Maybe humans are slowed down by our massive brains and all our extra processing, and have very slow reflexes, compared to other more agile creatures? Or maybe I’m a theoretical physicist who has no business speculating about this? This doesn’t really tell us anything about the fundamental nature of time, but it’s fun to think about how perception of it could be different.

But back to the question. How fast would your dog have to be going in order to get the benefits of special relativity, so that one calendar year on earth would be the same as one ‘dog year?’ Equivalently, how fast does a dog need to go so that the effects of time dilation will make it live as long as a human?

If a “dog year” is 1/7th of a calendar year, then we need her to go fast enough that her relativistic gamma factor is 7. I know this one off the top of my head- it’s 99% the speed of light. So if you want a puppy, born on the exact same day as you, to live a nice long happy (slow-mo) 80 years in your reference frame, all you have to do is send her away on a rocket going 99% the speed of light!

Since you’re getting this dog as a puppy, can I suggest a name? Laika was a stray dog, plucked from the streets of Moscow, and shot into space by the Soviets in 1957 to study whether a living passenger could survive the conditions of spaceflight. The difference is that your Laika is going to live a long and happy life exploring the cosmos, while the Soviet Laika only lived long enough to orbit the earth. It seems like a fitting tribute to me.



asked by Aryan M.

cover image credit: Wikimedia Commons


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