What is the biggest number?

The brain a complex machine.
My complex machine is overheating, from guesstimating the size of a hand to trying to use a laptop ad getting angry at it for not working in the same way the desktop does.
I swear when my laptop arrives I will be investing in a mouse. Grrrrrrr

So a cup of tea quick fix to relax and cool down my overheated fleshy machine. Whilst watching a show on BBC2 I think its called Infinite universe, ahhhhhhh with its talk of googles and grahams and now the question:
What is the biggest number?

and now I don't feel the effects of the relaxing with a cuppa so much, now I must crack open that unopened wine, Bet I can work out the answer then ; )

Good evening all
x