Einstein and Dark Energy

• However, now we see that there is indeed a cosmological constant term – but it acts in the opposite sense to Einstein’s original idea

• The Dark Energy implied by the non-zero value of pushes the Universe apart even faster, rather than adding stability to an unstable Universe, as Einstein originally intended.

• The dark energy density/critical density = 

• There are many theories for Dark Energy: vacuum fluctuations, extra dimensions, etc.