Dark Energy Flashcards
What does dark energy do?
Responsible for acceleration of universe
What do we expect gravity to do to expansion of universe?
Counteract it and slow it down
What does negative pressure mean in relativity?
Can get repulsive gravity
What does dark energy do different to normal gas?
Normal gas pushes outwards on things but dark energy pulls instead
Without dark energy what would universes age be predicted as?
8-10 billion years
What is the simplest way to get acceleration and leading explanation for dark energy?
Cosmological constant
What is a cosmological constant?
A constant energy density inherent in empty space which would exert negative pressure on space causing negative gravity
Particles flickering in and out of existence at microscopic scales because energy fields that describe gh have a zero point energy. Why is this prediction for being dark energy wrong?
Wrong by factor of 10^120
What is one problem with dark energy?
Fine tuning problem- case where we expect number to be 1 turns out to have some tiny value
What will happen to universe if matter dominated and cosmic density higher/lower than critical density?
•higher- re collapse in Big Crunch
•lower- expand forever
How do density parameters compare?
Dark energy>dark matter>baryons
How much do dark energy/matter and baryons cluster?
•dark energy probably not at all
•dark matter clusters a bit
•baryons cluster most
What percentage of total do baryons make up?
5%
What are baryons?
Mixture of visible matter in stars and gas and things too dark to see
What percentage of cosmic energy density does dark matter make up?
26%
