J. Goodman – May 2003

Quarknet Symposium May 2003

Neutrinos, Dark Matter and the Cosmological Constant

The Dark Side of the Universe

Jordan Goodman

University of Maryland

J. Goodman – May 2003

Outline

• Why do we care about neutrinos?• Why do we think there is dark matter?• Could some of it be neutrinos?• The search for neutrino mass – Solar Neutrinos

– Super-K– SNO– Kamland

• The accelerating Universe - Dark Energy – SCP – WMAP

J. Goodman – May 2003

Seeing Big Picture

J. Goodman – May 2003

Why do we think there is dark matter?

• Isn’t obvious that most of the matter in the Universe is in Stars?

Spiral GalaxySpiral Galaxy

J. Goodman – May 2003

Why do we think there is dark matter?

• In a gravitationally bound system out past most of the mass V ~ 1/r1/2

• We can look at the rotation curves of other galaxies– They should drop off

But they don’t!

J. Goodman – May 2003

Why do we think there is dark matter?

• There must be a large amount of unseen matter in the halo of galaxies– Maybe 20 times more than in the stars!– Our galaxy looks 30 kpc across but recent data

shows that it looks like it’s 200 kpc across

J. Goodman – May 2003

Measuring the energy in the Universe

• We can measure the mass of clusters of galaxies with gravitational lensing

• These measurements give mass ~0.3

• We also know (from the primordial deuterium abundance) that only a small fraction is nucleons

nucleons < ~0.04 Gravitational

lensingGravitational

lensing

J. Goodman – May 2003

What is this ghostly matter?

• Could it be neutrinos?• How much neutrino mass would it take?

– Proton mass is 938 MeV– Electron mass is 511 KeV– Neutrino mass of 2eV would solve the galaxy

rotation problem – 20eV would close the Universe

• Theories say it can’t be all neutrinos– They have difficulty forming the kinds of structure

observed. The structures they create are too large and form too late in the history of the universe

J. Goodman – May 2003

Super-Kamiokande

J. Goodman – May 2003

Hubble Law

J. Goodman – May 2003

The expanding Universe

• The Universe is expanding

• Everything is moving away from everything

• Hubble’s law says the faster things are moving away the further they are away

J. Goodman – May 2003

The expanding Universe

J. Goodman – May 2003

Supernova Cosmology Project

• Set out to directly measure the deceleration of the Universe

• Measure distance vs brightness of a standard candle (type Ia Supernova)

•The Universe seems to be accelerating!•Doesn’t fit Hubble Law (at 99% c.l.)

J. Goodman – May 2003

The expanding Universe

J. Goodman – May 2003

Energy Density in the Universe

may be made up of 2

parts a mass term and a “dark energy” term

(Cosmological Constant)

massenergy

• Einstein invented to keep the Universe static

• He later rejected it when he found out about Hubble expansion

• He called it his “biggest blunder”

m

J. Goodman – May 2003

The Cosmological Constant

J. Goodman – May 2003

What is the “Shape” of Space?

• Closed Universe >1– C < 2R

• Open Universe <1– Circumference (C) of a

circle of radius R is C > 2R

• Flat Universe =1– C = 2R– Euclidean space

J. Goodman – May 2003

Results of SN Cosmology Project

• The Universe is accelerating

• The data require a positive value of “Cosmological Constant”

• If =1 then they find

~ 0.7 ± 0.1

J. Goodman – May 2003

Accelerating Universe

J. Goodman – May 2003

Accelerating Universe

J. Goodman – May 2003

Measuring the energy in the Universe

• Studying the Cosmic Microwave radiation looks back at the radiation from 400,000 years after the “Big Bang”.

• This gives a measure of 0

J. Goodman – May 2003

Recent Results - 2002

0=1 nucleon

J. Goodman – May 2003

WMAP -2003

J. Goodman – May 2003

WMAP - 2003

J. Goodman – May 2003

What does all the data say?

• Three pieces of data come together in one region

~ 0.73 m~ 0.27 (uncertainty ~0.04)

• Universe is expanding & won’t collapse

• Only ~1/6 of the dark matter is ordinary matter (atoms)

• A previously unknown and unseen “dark energy” pervades all of space and is causing it to expand and accelerate

J. Goodman – May 2003

What do we know about “Dark Energy”

• It emits no light• It acts like a large negative pressure

Px ~ - x

• It is approximately homogenous– At least it doesn’t cluster like matter

• Calculations of this pressure from first principles fail miserably – assuming it’s vacuum energy you predict a value of ~ 10120

• Bottom line – we know very little!

J. Goodman – May 2003

Conclusion

• total = 1.02 ± 0.02

– The Universe is flat!

• The Universe is : ~1/2% Stars

~1/2% Neutrinos

~27% Dark Matter (only 4% is ordinary matter)

~73% Dark Energy

• We can see ~1/2%• We can measure ~1/2%• We can see the effect of

~27% (but don’t know what most of it is)

• And we are pretty much clueless about the other 3/4 of the Universe

There is still a lot of Physics to learn!