Dark Matter, Dark Energy, and Dark Gravity Alan Heavens Imperial - - PowerPoint PPT Presentation

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Dark Matter, Dark Energy, and Dark Gravity Alan Heavens Imperial - - PowerPoint PPT Presentation

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Dark Matter, Dark Energy, and Dark Gravity Alan Heavens Imperial College London ! Friends of Imperial College 28 January 2014 Space Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may

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Dark Matter, Dark Energy, and Dark Gravity

Alan Heavens Imperial College London

!

Friends of Imperial College 28 January 2014

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Space…

“Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” - Douglas Adams

Photo: Jill Furmanovsky

NASA/STScI

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Credit: ESO/S.Brunier

100,000,000,000 stars

Birth of modern cosmology

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Doppler shift

Credit: NASA/Goddard

Credit: R. O’Connell

Credit: San Jose State University

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Vesto Slipher

Credit: Lowell Observatory

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Hubble’s law

Speed ∝ distance v = Hr

From: Studyblue

Credit: CalTech

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Big Bang

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Will it always expand?

Gravity should slow it down If it is dense enough it will stop Measured by Ω Ω=1 is equivalent to a few atoms per cubic metre Ω>1 Ω<1

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Ordinary matter

Credit: N. Wright

Credit: Pearson Education

£5.60.

Credit: Amazon

NOT ENOUGH!

Ωnormal matter = 0.04

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Dark Matter

Fritz Zwicky (1937)

Coma cluster

Credit: NASA/JPL

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Ωmatter ' 0.27

Credit: Mark Whittle, University of Virginia Emilio Segre Visual Archives/AIP/SPL

Vera Rubin

drawception.com

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Bullet cluster

Markevitch et al 2002 Clowe et al 2004

Hot Gas (X-ray) Dark Matter (Lensing) Galaxies

What is the dark matter?

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Light from the Big Bang

Arno Penzias and Robert Wilson

Credit: Pearson Education

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“Cosmic Microwave Background (CMB)”

Credit: CalTech

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Spectrum of the CMB

Universe must have been very dense

Credit: NASA

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Geometry of the Universe

Planck satellite

Credit: ESA and Planck team, & J. Cramer for the sounds

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Universe is ‘flat’

Einstein: geometry and mass content are related What is the rest? This is referred to as DARK ENERGY

Ωtotal = 1

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Supernovae

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Type 1a Supernova

Don Dixon

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New one!

Discovered by UCL undergraduates and supervisor These are ‘standard candles’

astronomygcse.com

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Measuring the expansion history

Speed Distance

Non-decelerating Universe

Fainter Brighter

Decelerating Universe

Further back in time

Should appear brighter

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They appear fainter…

!

Universe is ACCELERATING!

Credit: High-z SN team

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Nobel Prize for Physics 2011

Saul Perlmutter Brian Schmidt Adam Riess

For the discovery of the acceleration of the Universe

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How to get acceleration

Modify gravity - need something to ‘push’ Einstein’s cosmological constant “The biggest blunder of my life”

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General Relativity

Matter tells space-time how to curve Space-time tells matter how to move

Credit: wikipedia

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Possibilities 1 and 2

Possibility 2: the vacuum has energy and other strange properties (negative pressure, repulsive gravity) Gµν = Tµν Gµν − Λgµν = Tµν Gµν = Tµν + Λgµν Gµν = Tµν + T new

µν

Possibility 1: Einstein was right: the cosmological constant exists curvature : matter

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Vacuum energy

Particle-antiparticle pairs 10120 times too much energy If there is a vacuum energy, we have no idea why it has the energy it has

Tim Jones

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Dark Energy

Possibility 3: some new field or form of matter might be driving the acceleration ‘Quintessence’ or ‘Dark Energy’ Expansion history may be a little different

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Exotic possibilities

Einstein Gravity works fine on small scales

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Possibility 4: Extra dimensions

Universe may have more than 3+1 (space+time) dimensions Gravity ‘leaks out’ into the bulk Gravity in our 3+1D universe is modified

Braneworlds

Credit: DAMTP

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How can we tell?

If the gravity law is changed:

!

  • it changes the way the

Universe expands

  • it changes the rate at

which structures grow

  • it changes how light gets

bent by matter

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Weak gravitational lensing

Credit: S. Colombi

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Credit NASA/STScI

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Testing gravity with lensing and galaxy surveys

Simpson et al 2013

Growth rate agrees with Einstein Light bending agrees with Einstein

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Λ

So far, it seems Einstein may have been right

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EPFL

Launch 2020 A thorough test:

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Credit: George Dvorsky

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