[ncmncm]

My CPU can't, but it is theoretically possible to make a CPU that could.

[plasticchris]

do you mean that a turing machine can't simulate the universe but some other kind of cpu (i.e. quantum) could?

[jhoechtl]

This is all very theoretical so ... a turing machine can simulate a universe as it assumes infinite memory

[ncmncm]

No, I mean that it is physically possible to perform an unlimited amount of computation on a fixed amount of energy, if you are willing to wait long enough. Nobody has built hardware that has this property.

[NathanielK]

1W is one joule per second. With unlimited time, you also have unlimited joules trickling out.

[ncmncm]

You are not getting this.

You can do an unlimited amount of computation on one joule. One watt-second, if you like.

Not an infinite amount of computation, but any finite amount.