- Particle Generation and Their Masses
- Baryon Content of the Universe
- Matter (light + dark) Density in the Universe
- Nature of the Dark Matter
- Formation of Galaxies
- Large Scale Structure
- Determination of Cosmological Parameters
Particle Generation and Their Masses:
Masses of quarks endowed during some phase transistion? -->
sets the entropy of the Universe is well?
SU(10), SU(16), SU(??) --> how will we ever know which one is correct?
Baryon Content of the Universe:
Places where Baryons can reside:
Constraints on Baryon Density:
Conclusion --> We don't yet have an accurate census of the repositories
of baryonic matter in the Universe
- Abudances of helium, lithium --> 0.04 -- 0.07 (for h =1)
- Number density of galaxies
- Observations of Deuterium --> if believed then baryon density
is around 0.02
Matter (light + dark) Density in the Universe:
- Upper limit on Baryon density is likely to be 0.07.
- Galaxies (all types) themselves contribute 0.04 at most
- Inflation demands Omega = 1 --> Observationally, most
evidence points to Omega = 0.2
Conclusions: Dynamical determinations of Omega are quite difficult
but over most scales they indicate a value less than 0.2
Nature of the Dark Matter:
How do we know its there?
What is it?
- Baryonic Candidates --> stellar remanats, brown dwarfs -->
fine as long as the Universe is open
- If Omega = 1 --> its a particle
Detecting Dark Matter:
- MACHO Lensing survey
- MACHO is hard and may not produce unambiguous results
- SSC --> dead
- Solar Neutrino Experiment --> suggest small mass for neutrino?
--> note: for h=1 need neutrino mass of around 30 eV for closure
- Other Accelerator Experiments
Formation of Galaxies
This is understood in principle
In practice, there are lots of difficulties:
- Unknown initial conditions
- Unknown role and nature of dark matter
- Unknown primoridal fluctuation spectrum although there
are now constraints from COBE
- Not predicted in HDM scenarios
- Too many galaxies form in CDM scenarios
- Galaxy formation has never been observed!
- Oh hell let's just simulate it
Large Scale Structure:
- Determined from Redshift Surveys
- Extant surveys indicate three complicating themes:
- We haven't surveyed a fair volume of the Universe yet
- There is power on very large scales
- There are suggestions of motions on very large scales which
violates COBE anisotropy constraints --> galaxies are not the
same at the 10% level!
When redshift surveys are combined with the COBE constraint one
can make the following definitive statement:
Standard, biased CDM can't account simultaneously for both the
small scale and large scale structure. Unbiased CDM does not help
Now one is driven to consider:
- Mixed dark matter
- Tilted Inflationary scenarios (non-Gaussian distributions)
- Non-zero Lambda
So, things are getting complicated and there are not yet good enough
observations to distinguish between the above combination of models
(meaning that theory can now fill the literature ).
Determination of Cosmological Parameters:
Hubble Space Telescope Key Project --> determination of h
First results (Oct. 94): h = 0.8 +/- 0.17
When corrected for small systematic errors h = 0.9 +/- 0.17
But hey there are now stars that
are older than the Universe!
GO WHERE THE DATA LEADS --> Lambda is not ZERO!
The Electronic Universe Project