1. Thought experiment 1 Brain Snatched

2. Do we have any REASON to suppose that the earth and everything on it really exists? Or could it all be an illusion!

3. A brain in a vat Colin Spiggott about to relax and watch the film Invasion of the body snatchers

4. Aliens from another planet

5. A night of nightmares

6. Neptune

7. Removing the brain

8. Brain in a vat

9. Connected to the super computer

10. It’s not real, it’s all an illusion

11. Carrot to goldfish

12. Immersed in a computer program

13. Wake up…it’s a nightmare

14. Hideous Neptunian alien

15. ‘This is you Colin’

16. How do you know that you are not a brain in a vat?

17. 2 Hypothesis 1. What you see around you is all virtual – An illusion. You are really a disembodied brain floating in water connected to a sophisticated super computer that generates perfect experiences as we know them What you see around you is real

18. What justifies that belief? In order to know something you need grounds for believing it. You must be justified in believing what you do. So in order to know that what you see is real and not virtual, you must be able to justify that belief. But it seems you cannot justify it. So, astonishingly, it seems you do not know that what you are now experiencing is real.

19. An astonishing conclusion A sceptical conclusion Sceptics claim that we do not know what we might think we know. The claim that we do not know anything about the world around us is called scepticism. http://www.youtube.com/watch?v=ursdoT66JlU

20. Lisa the sceptic Watch the episode from 6 minutes onwards