[thedoc (OP)]

Arun asked the Naked Scientists:
   If there is light and no dark, what could be the third thing in the universe?
What do you think?

[Bill S]

Hi Arun, I don't understand the question.  That's not unusual [], but I think you might need to be a bit more specific.

[alancalverd]

The Other Thing.

[Colin2B]

Forget the third thing, you need to find out what the second thing would be?

[evan_au]

If there is light and no dark

To expand on Colin's answer: Dark is the absence of Light.
So you have only described one thing in the universe (Light).

What is the second thing? (to a materialist, maybe matter?)

[Colin2B]

What is the second thing? (to a materialist, maybe matter?)

I like that answer. Once you get solid matter you get a shadow, hence dark.
So dark is now the 3rd thing :-)