If I travelled to the 12th century and returned 1 year later would I have spent a full year there or less .?

Question

I'm looking for a different take on the Twin Paradox. I'm not travelling through space at high speed but back in time.
I hope the answer is that I thought I'd been there a few months but discover when I return I was there 1 year.

Answer 1

The summation of all Earth's velocities (speed + direction) over a 12 month period is so close to being the same in the 21st century as in the 12th century, that the overall time flow will have been the same.

In other words, no time dilation.

The frame of reference of Earth in 12th century is equivalent to that of Earth in the 21st century.

Therefore, 1 year then is the same as one year now.

If you were to compare a shorter period (say two months) over an interval when the Earth is moving one way (at 30 km/s) in the 21st century and when the Earth is moving the other way in the 12th century, then you could assume a difference of 60 km/s between the two frames of reference.

Two months = a little over 5 million seconds.

Perceived interval : 5 million seconds * SQRT(1 - v^2/c^2)
v=60 km/s c = 300,000 km/s
v/c = 0.0001
(v/c)^2 = 0.00000001
1 - v^2/c^2 = 0.99999999 (eight nines)
SQRT = 0.9999... (four nines plus some small stuff)
t' = 4,999,999.975 seconds

difference = 0.025 second (= 1/40 of a second)

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If you could rig the time machine so that your return is one second after your departure (in 21st century), then your body will have aged 5 million seconds (minus 1/40 ?) while your twin has only aged one second.

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One big problem with such scenarios is that science-fiction stories assume that travelling to the past does not involve any spatial distance.

However, the Earth in the 12th century was nowhere near the location in space where it is now. We orbit the Sun at 30 km/s and the Sun orbits the Galaxy at 200 km/s relative to the Galactic centre. The Galaxy moves at some 400 km/s relative to the CMB radiation...

So your twin will recover a frozen corpse, damaged by exposure to vacuum.

Answer 2

If you can travel back in time to a certain point, you should be able to travel back to the future to a certain point. So, if you leave now, you could come back into the next instance. People watching you leave would think you had just flipped around backwards, grown a beard and mustache, and had your clothing transformed. You would probably smell bad too!
You would "lose" the year you spent in the 12th century. Unless you set your "time machine" to bring you back one year later than when you left.

PS. Travelling through time is easy, it's travelling through time AND space thats hard. Everything constantly moves at incredible speed, and traveling through time means having to move to it's new location. Keeping a fix on a relative local is next to impossibly.

Answer 3

Imagine traveling 12 years into the past and you've forgotten to allow for the Earth's angular momentum and instead of arriving on the Earth 12 years prior you reach the point in space where the Earth was but one second off from the exact 12 year time frame! You're now just floating in raw space with no protection and have infinite regrets!

Answer 4

When you start thinking about time travel, you're completely in the realm of science fiction. In such a realm, you are free to make up whatever rules you wish, since clearly you are choosing to ignore the rules that actually exists.

In terms of time travel, if you travel BACK in time, and then travel FORWARD in time to a point one year later then when you left, the amount of time you actually spent in the past could be ANYTHING (1 minute or 100 years). If, in the fiction you are creating, you impose rules on how the time travel works, you can make the fiction work out in whatever way satisfies the dramatic needs of the story.

Answer 5

if you spend a year in the 12th C then you will have spent a year there

whether or not you were "missing" from the 21st C for a year is a whole different ball game

Answer 6

i got a question for you.

if you travel 1000 years back in time, do you have any idea just how FAR the Sun has traveled in a 1000 years? wouldnt you just POP out into space somewhere?