LOL

[conuly]

http://www.sheldoncomics.com/archive/130916.html

So, my mother and I were talking about time travel. Her big plan with time travel is to go back in time, exchange modern bills for older series bills, and do her groceries on the cheap. Which, quite aside from being the very definition of a mundane utility, has a few practical problems with it.

Lets take a shopping trip in 1980. She obtains $100 in $20s from the 1980 series. It's not clear if she's doing this exchanging now or in the past, but I think making the exchange now creates fewer logistical difficulties, though the end result will be the same.

She goes back in time and does her shopping, using those bills. But those bills already exist! With every trip, she is devaluing the money by adding 5 new 20s to the mix. Worse, if she continues this shopping, sooner or later those bills are going to meet! It'll be a paradox to beat all paradoxes. The world will explode! And why?

Because my mom wanted to pay less for coffee.

Comments

[steorra]

I don't understand how swapping old and new bills will let you get groceries for cheap.

[conuly]

You swap for face value today. Due to inflation, that means that when you go back in time your money is worth more. If I go back to 1980, every $20 bill will buy as much as $56.77 would today. That's a lot of savings! I might need only $45 to do the shopping that takes me $130 nowadays.

But you can't spend bills from the 2000 series in 1980. They don't look the same.

[conuly]

Of course, what my mother is forgetting is that some things are easier to obtain now than then. When I was a kid, stores stocked at most three kinds of apple. Now, even the crappiest supermarket will stock at least five. So you might not be able to do all your shopping in the past.