Answer: Inflation and Positive interest rates.
Explanation:
If a dollar today is worth more than tomorrow, this is primarily due to the inflation and positive interest rate in an economy. Suppose there is a further increase in the inflation rate in the near future, so the quantity of goods which I am buying today from the given $10 is more the quantity of goods which I will get in the future.
This clearly shows that the value of dollar decreases because of inflation rate. If a country is having negative inflation and negative interest rate then this will not be the case. In this case, the value of dollar improves.