Transcript Lect4.DarkEnergy.Ear..

Coming up
• Chapter 7 on Dark Energy
Read Now: Coming next
Putting it together
Puzzles and Future Frontiers
Our Cosmic Future
Does the Cosmos know us?
Are We Alone?
Searching for Life
Spring is Springing!
Feb
Daylight is
increasing
by about
20 mins
per week
Jan 4
Mar 12
http://www.timeanddate.com/sun/usa/seattle
Review Questions
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How did density contrasts change from t=1 min to
400,000y (start of transparency)? Why?
Ditto from 400,000y until now? Why?
Was dark matter needed in order for galaxies to
form? Why?
Why couldn’t galaxies form
• Before the radiation of the CMB was released?
• >≈1 billion years after the CMB was released?
Why are we confronted by the Cosmic Conundrums?
• Flatness,
• Ripple (“Ideal Inhomogeneity”),
• Horizon,
• Exotic Particles
Factor or 1043
Inflation: Review
•Was Inflation
an Explosion?
•Was it Hot?
•Did it
homogenize the
structure of the
cosmos?
Inflation @ T > 10+29 K
WHAT: Sudden growth of the cosmic horizon
WHEN: 10–35 s ABB
WHERE: everywhere
 Space inflated (multiplied) in scale by a
factor of 1043 between 10–35 and 10–33 ABB.
 the horizon (radius of spheres of influence) ballooned
from 10-28.5 km to 10+14.5 km ≈30 l.y. Size of proton,10–
13 cm, grew to 1025 km = 1012 l.y. = 100x present
horizon!
 Regions once in close touch suddenly lose touch and
no longer influenced each other’s evolution
 However, these regions still share their
“inheritance”– physical properties, forces, &
processes
Inflation
Inflation
WHY: Energy unleashed by the
transformation of the
“Grand Unified Force”
?
Factor or 1043
Inflation: Why Believe it?
Physics fills in the huge gap in time from
from 10–36 s to the era of transparency
observers
geeks
Ωm = 0.3!
Ωm = 1!
The Outlook of Observers
Best observations implied r/rc = Wmatter = 0.3 with ≈ 10% uncertainties
Important note:
Photons of energy E have an “effective mass” E/c2 and contribute to Ωmatter just like mass
The Outlook of Theoreticians
The Outlook of Theoreticians
Relative Strength
Theoreticians require r/rc ≈ 1 in order for galaxies to
form from the CMB ripples before cosmic expansion
dropped the density of the ripples too much.
The Outlook of Theoreticians
r/rc = 1
No condensation
of galaxy clusters
Model estimation
www.astro.ucla.edu/~wright/cosmo_03.htm
Premature “crunch”
↑
Now
ACCOUNTING FOR THE STUCTURE THAT WE SEE ALL
AROUND US, r/rc MUST BE UNITY TO WITNIN
1 part in 2235 sextillion
Surprise!
Dark Energy Changes the Game
empty universe
open universe
flat universe
closed universe
Preview: Dark Energy rules!
10–43 s
Matter (Gravitation)
Dominates
Dark Energy
Dominates
The expansion of the Universe is accelerating.
Here’s the First Evidence
Deviation
Distance
The data are pretty
darn good and an
unexpected pattern
emerges
Pre-1995 data
Since 1998:
Two other very different
types of observations also
point to dark energy.
CONFIRMATION!
Discovery of Dark Energy
(using SN-Type Ia’s as standard candles)
The presence of dark energy is
confirmed by other methods:
CMB ripples
“acoustic noise”
Space distortions
Supernova best results
WL
Ωtot = Ωm + ΩL
Ωm = matter (grav)
ΩL = dark energy
Goldilocks
Wmatter
Add “gamma-ray” bursters as standard
candles
Various independent best results
“Error ellipses”. Best
estimate of Ωm & ΩL
Supernovae
CMB ripples
Structure of nearby
clusters of galaxies
and g-ray bursters
Ωtot = Ωm + ΩL
Ωm = matter (grav)
ΩL = dark energy
= 0.3 + 0.7
= 1.0023 ± 0.0055
Wmatter
Goldilocks
mid 1990s
of dark energy)
2016(before
(afterdiscovery
latest observations)
In the 1980s the best observations implied r/rc = Wm = 0.3 with ≈ 10% uncertainties
Best observations imply Wtot = 1.0023 ± 0.0055 uncertainties
OPEN UNIVERSE
FLAT UNIVERSE
Goldilocks
0.7
0.3
The Evolving Cosmic Energy Budget
Throughout
cosmic history
380,000 y ABB, when
Universe became
transparent.
Types of Model Cosmic Outcomes
(Ωm= 0.3, ΩL= 0.7)
(Ωm= 1.0, ΩL= 0)
(Ωm= 5.0, ΩL= 0)
Ωtot = Ωm + ΩL
Ωm = matter (grav)
ΩL = dark energy
Future →
Classical (pre D.E.)
Flat universe
(model)
Forcing Flatness
Einstein’s Field Equation including his L fudge
geometry and curvature of space
=0
+
–
T describes the
insert this with
distribution of
mass-energy.
(repulsive).
G is Newton’s
constant of
gravitation
(attractive)
L>0
Fine-tuning L
gives zero
curvature
Dark Energy and motions
We can rewrite the field equation in a
local environment. In this case the ugly
tensor math in Einstein’s field equation
becomes manageable (O&M AppA p274).
Net acceleration of two
nearby isolated bodies
separated by distance
repulsionr
attraction
acceleration = –GM / r + L × r / 3
2
Based on
Equation
A18
Newton’s Law:
decreases as
separation = r2
increases with
separation = r
Dark Energy and motions
The right side contains an attractive force,
gravity, and a repulsive term generally
described as dark energy.
These terms act in opposition.
attraction
repulsion
accel = –GM / r + L × r / 3
2
L ≈ 10-122 !
If r is increased the force of gravity decreases and the repulsive “force” increases
in strength. So once the Universe expands it can’t stop. Similarly, if the Universe
shrinks a little then the opposite occurs. The contraction is not stoppable.
In summary, this equation predicts that the Universe is unstable (page 214).
This deeply troubled Einstein. He later regarded the L term as superfluous.
The expansion starts to “run away” a few billion years after the L term dominates:
1/2
separation µ exp [(L / 3) t]
Today the L term seems to give an accurate description of the way in which Dark
Energy works. That’s not to say that the term is otherwise justified.
Dark Energy and
Cosmic Fate
Goldilocks
Ωtot = S Ωm + ΩL
best model with dark energy
0.3089±0.0062
open universe without dark energy
flat universe without dark energy
closed universe without dark energy
ΩL
Wtot = 1.0023 ± 0.055
0.6911±0.0062 Planck (2015)
now
2x
now
3x
now
Adapted from O&M Fig 7.2
Summary:
Dark Energy and
Cosmic Fate
ΩL = 0.7
Bye bye love
Bye bye happiness
Hello loneliness
I think I'm-a gonna cry-y
–– Everly Bros (1957)
Do you really believe this
stuff?
Pause:
CREDIBILITY (legal style)
Standards for establishing truth
The “Burden of Proof”
• The legal system requires that decisions of
guilt or innocence be made with solid but
fragmentary evidence, and that they be made
expeditiously by peers during the course of a
trial. This is challenging.
Standards of truth
• Civil vs Criminal thresholds of guilt
– (http://www.rbs2.com/cc.htm)
– invent a "spectrum of proof"
• from unproven (0) to proven (100)
– Civil Trials. (burden of proof usually on plaintiff;
usually fines, no jail) standard exceeds ?
• standard of proof is the “preponderance of the evidence”.
– Criminal Trials. (burden on the state; many forms of
punishment) standard above?
• the burden of proving guilt is on the prosecution.
• standard of proof is “beyond a reasonable doubt”
Credibility scale
0%
100%
Final Paper:
“My Critical Review of the Big Bang Theory”
• Identify three vulnerabilities and
reasons.
– Be concise. Stay on point. No long reviews of BB
model.
• YOUR VIEW of the model’s credibility.
– State your unambiguous conclusions at the start.
Then explain/ justify them in your own words.
• Guidelines of “burden of proof”
–Civil Trials
–Criminal Trials
Credibility scale
0%
100%
Attributes of a good hypothesis
How well do the Big Bang Model and its key elements fare?
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Consistent with observations and facts
Foundation of repeatable experimental data
Valid methodology and underlying physics
Predictive and repeatable
Experimentally falsifiable
Cognizant of measurement precision/error
Cognizant of methodological biases/limits
• Anonymously evaluated by peers and deemed meritorious
for publication in professional journals
• Considers/evaluates alternate successful interpretations
The Future
(now)
frigid
^
2.7 K
Before Inflation:
The “Planck Era”
The Era of Quantum Fluctuations
AKA the era of mystery: <10–43 seconds
The quantum theory of black holes:
where relativity and quantum mechanics collide
Now
1 year
1031 K
@ 10-43 s
Expansion cools
the Universe
1 second
“logarithmic” units
Time is Temperature
2.735 K
@ 4 X 1017s
Introduction to Celestial Light
“Photons”
“wave packets”
Photons carry the energy of light
Energy/photon = constant / l = hc / l
= 2 x 10–16 / l(cm) = 3.3 x 10–15 j
A 100-watt light bulb emits ~3 x 1016 photons in one second
The Sun emits 2 x 1049 photons per second
Over its 1010 yr lifetime the Sun will generate 6 x 1066 photons
The Sun is one of about 1022 stars within the visible universe
LOTS OF PHOTONS! And many many more from the CMB!
Introduction to Celestial Light
• Energy and mass are equivalent, so photons with
energy E have an equivalent mass mph
• The mph is very small (now)!
– Even so, the path of a photon is affected by the gravitational distortion of space just like a particle!
higher energy photons
Doppler shifts in an
from the Big Bang
expanding universe
All moving masses MUST remain on
the trampoline. No shortcuts!
Light at 10–43 seconds
• Incredibly intense.
• Typical photon energies ~108 j
 Blinding! 1023 x energy of visible light
 Every photon has about the energy
output of Coulee Dam in 1 second
 The equivalent mass is 0.1 milligram
The numbers of
cosmic photons have
never changed much,
but their energies
have now dropped by
a factor of 1031 as the
Universe expanded
The first light: < 10–43 sec
• At extreme energies the equivalent mass of a
photon can become that of a black hole of the
same size and mass.
• This happens when the wavelength of the
photon, lph, = 10-35 meters = “Planck length”
• Eph = 3 billion joules*,
• mph = 3e-8 kg
= 0.03 milligrams**
• The kinetic energy of a huge
coal train @ 100 miles/second
** about 1/25 the iron content
of a raisin
The first light: < 10–43 sec
– The Planck length is the size of a photon whose
energy is sufficient to form a black hole. l = 10–35 m.
– What happens inside this black hole cannot be known
without a theory of quantum gravity.
– It would take light 10-35 / 3x108 ≈ 10-44 sec to cross the
black hole. That’s the “Planck time”.
– The development of a theory awaits a better
understanding of the cosmic origin of forces
– Current physics begins to be useful after ≈ ten Planck
times, 10-43 sec. That’s the end of the “Planck Era”.
The first light: < 10–43 sec
• Supergravity (the precursor of today’s four familiar forces) first
becomes an force after one Planck time. How that happened is still
a mystery.
• The creation of gravity may have been the first known “phase
instability” that initiated the stretching of space from quantum to
larger sizes.
• Once gravity exits as an entity we can use a theory of gravity (such
as General Relativity) to describe the growth and shape of space.
• Other future forces separate into a scheme called “GUT” (Grand
Unified Theory). GUT is not yet understood.
• The GUT force breaks into independent strong nuclear and
electroweak forces after 10-35 seconds.
• That may have been a second ‘phase instability of space’ that
resulted in the era of inflation.
Before the
Big Bang
Before the Big Bang:
The Quantum “Foam”
Fluctuations Exist/Persist
“Planck Era” ≈ 10–43 s,
T ≈ 10+31 K
Cosmic Foam. The Principle of Uncertainty suggests that
during any 10–43 s space time can not be exactly measured
or determined since it can exist one moment and not exist
the next — all without violation of any laws. Universes come
and go continuously. Some randomly “pop loose”, expand,
and exist for “longer”(whatever “longer” means).
Predictions of
the Future
http://www.bbc.com/future/story/20140105-timeline-of-the-far-future
106 to 108 y
108 to 1010 y
1011 to 1020 y
1014 y
1020 y
The Cosmic Future
Short-Term Cosmic Forecast
(< 100× present time)
 Darker, colder, and less dense
 Existing gravitationally bound systems will persist
(and slowly become even denser)
 Formation of white dwarfs and neutron stars will
deplete the reservoir of interstellar dust and gas.
 High-mass star production will drop off. Supernova
rate will go down, as will the production of most
heavy elements.
 All star formation ends once the ISM is depleted
 Friction results in the Earth’s orbital death spiral
The Cosmic Future
Medium-Term Cosmic Forecast
(< 100× present time)
 The “Cosmic Sprawl”: Acceleration of the Cosmic
Expansion (if it continues) makes everyplace lonely
 100 trillion (1014) y: All ISM depleted
 Star formation ends
 The last red giant becomes a white dwarf
 Occasional flares as brown dwarfs collide
 Galaxies fade as their white dwarfs cool
 All chemical and nuclear energy depleted
The Cosmic Future
Ultimate Cosmic Forecast
(> 1010× present time)
 1039 y: white dwarfs die from proton decay and
neutron stars decay from neutron beta decay
 10100 y: last black hole decays from Hawking radiation
 > 10100 y: a fate of photons, electrons, positrons
 > 10100 y: frigid and orderless (but lumpy) ‘sea’ of
photons (sub radio energy) electrons, positrons.
The 2nd Law and local quantum effects rule!