Laptop for university 2012, 10 points for best answer.?

I'm looking for a laptop for university next year in which I will be studying physics. I'm not good at computer's at all and just telling me the required specs isn't really that much of a help. I have around £400-£1000 to spend on a laptop so I want it to be good. The main things im looking for is:

Good battery life (6+ hours), very reliable meaning it should last me for 4 years or atleast an extended warrenty, relatively light (no more than like 3.5 kilograms), be very fast and able to run multiple programs at once.

I have no idea about certain brands and some people say others are rubbish compared to some and I just confused so I someone could give me specific models or good laptop makes it would be great.

Thank you so much.