Is it possible for a slow computer to beat the world mining Bitcoin?
It is of course possible... however it is incredibly unlikely!

Mining with a CPU has not been profitable since the earliest days of bitcoin, the expected time to find a block is likely on the order of centuries at this point, and by that time you'll have burned much more in electricity costs than the eventual block reward.

So, as an experiment you could try, but if it costs you even just $5 worth of electricity a month, you would actually have better odds spending that money on a lottery ticket!