The Fate of The Universe

Will the universe continue expanding forever?

Does the universe have enough kinetic energy to escape its own gravitational pull?

Fate of a Launched Cannonball

Fate of universe depends on the amount of dark matter.

Critical density of matter

Not enough dark matter

Lots of dark matter

Amount of matter is ~25% of the critical density, suggesting fate is eternal expansion.

Not enough dark matter

But expansion appears to be speeding up!

Dark energy?Not enough dark matter

Estimated age depends on both dark matter and dark energy.

old older oldest

Thought Question

Suppose that the universe has more dark matter than we think there is today. How would that change the age we estimate from the expansion rate?

A. Estimated age would be olderB. Estimated age would be the sameC. Estimated age would be younger

Thought Question

Suppose that the universe has more dark matter than we think there is today. How would that change the age we estimate from the expansion rate?

A. Estimated age would be olderB. Estimated age would be the sameC. Estimated age would be younger

Is the expansion of the universe accelerating?

The brightness of distant white dwarf supernovae tells us how much the universe has expanded since they exploded.

An accelerating universe is the best fit to supernova data.

Topology(shape) of The Universe

• Over short distances even a curved Universe will appear flat.

• If the Universe is curved that means that the shortest distance betweeen two points is not a straigth line … it is a curve.

– Do aircraft follow a straight line when the fly from London to Hawaii?

– NO! they followed the curvature of the Earth.

– But over short distances aircraft appear to move in a straight line.

The inflation of the universe flattens the overall geometry like the inflation of a balloon, causing overall density of matter plus energy to be very close to critical density.

Topology(shape) of The Universe

• The curvature and topology (the shape) of our universe is directly related to the critical density.

• However, we may only be able to see a small part of our universe since photons further away that 14 billion light years have not reached us yet.

• Our universes appears to have the CRITICAL DENSITY and hence is flat.

• But like an ant walking on a large sphere … maybe it only appears flat.

The overall geometry of the universe is closely related to total density of matter and energy.

Density = CriticalExpand forever

Density > CriticalWill eventually stop expanding and collapse ‘big crunch’

Density < CriticalWill expand forever

The Ultimate The Universe• Density > ‘Critical Density’, the Universe will evenually

collapse in a big crunch.– The opposite of the big bang.

• Density = ‘Critical Density’, the Universe will expand forever but very slowly.– It will reach zero velocity at infinite time.

• Density < ‘Critical Density’, the Universe will evenually expand forever, but very quickly.– A cold death, the distance separating galaxies will be enormous.

– Stars in galaxies will eventually burn out when they run out of gas.

• Current measurement suggest that our Universe has a density equal to or very nearly equal to the critical density.