Transcript Dark Matter and Dark Energy

Dark Matter and Dark Energy
Just because something is unknown does not make
it unknowable
Total Mass/Density of the Universe
Dark Energy makes up
72% of the total massenergy density of the
universe. The other
dominant contributor is
Dark Matter, and a
small amount is due
to atoms or baryonic
matter.
Most of the universe is dark matter
and dark energy.
• Most of the mass-energy, about 95%, in the
universe is ‘dark’. By dark we mean that it
does not emit any form of electromagnetic
radiation.
• Dark energy and dark matter have not been
directly observed but they have been inferred
from observations of a wide variety of
phenomena. There existence is vital to the Big
Bang Theory.
Dark Energy
• Dark Energy is a hypothetical form of energy
that exerts a negative, repulsive pressure,
behaving like the opposite of gravity.
– Without dark energy, astronomers would not be
able to explain why the galaxy is still increasing in
size, in fact its expansion is accelerating, when
gravity should make it contract.
– More is still unknown than known about dark
energy.
Dark Energy
This diagram shows
changes in the rate of
expansion since the
universe's birth. The more
shallow the curve, the
faster the rate of
expansion. The curve
changes noticeably about
7.5 billion years ago,
when objects in the
universe began flying
apart at a faster rate.
Astronomers theorize that
dark energy is the reason
for the faster expansion.
Dark Energy
• Astronomers know how much dark energy
there is because they know how it affects the
Universe's expansion.
• Other than that, it is a mystery. But it is an
important mystery that needs solving. Why
does it need solving?
– Because everything ever observed with all of our
instruments, all normal matter - adds up to less
than 5% of the Universe..
Dark Energy
• Dark Energy, at this point in time, is not
directly observed, but has to be inferred from
observations of gravitational interactions
between astronomical objects.
• One explanation for dark energy is that it is a
property of space.
– Albert Einstein was the first person to realize that
empty space is not nothing. Space has amazing
properties, many of which are just beginning to be
understood.
Dark Energy
– Einstein postulated, as part of relativity, that
"empty space" can possess its own energy, which
gave rise to the idea of dark energy and the role it
plays in the universe.
– Because this energy is a property of space itself, it
would not be diluted as space expands.
– Einstein also postulated that it is possible for more
space to come into existence and as space comes
into existence, more of this energy-of-space, our
dark energy, would appear.
Dark Energy
• Quantum theory has its own explanation for how
space acquires energy that is very different from
relativity – postulates the existence of virtual
particles.
• Besides relativity and quantum theory, there are
other explanations, though they are not as
popular among researchers.
• It is possible that relativity and quantum theory
are both incorrect and a new theory of gravity is
needed.
Dark Energy
• What is known is that
astronomers/astrophysicists need more and
better data.
Dark Matter
• Dark Matter is still very mysterious.
– In the universe, gravitational lensing occurs in places
where there is no apparent matter.
– So we see what Einstein predicted, and was shown
during the solar eclipse, in places without large bodies
where light should not bend.
– To explain this odd behavior, physicists hypothesized
the existence matter that we cannot see.
– We have not seen dark matter but we can infer it
indirectly by its gravitational effect.
Dark Matter
• Inference from observations of
– the motions of stars and gas in galaxies, cluster
galaxy radial velocities, hot gas properties of
clusters, and gravitational lensing of distant,
background galaxies by foreground galaxy clusters.
• Basically, something is getting in the way that cannot be
seen – it screws up our predictions except when matter
is present.
– So there is a good deal of circumstantial evidence
that suggests large amounts of Dark Matter exist.
Dark Matter
• Dark matter is sometimes described as the
scaffolding of the universe on which all visible
bodies (suns, galaxies, planets, etc.) are built.
Big Bang Nucleosynthesis
• Big Bang Nucleosynthesis (abbreviated BBN) refers to the production of nuclei other than
those of the lightest isotope of hydrogen
during the early phases of the universe.
• http://astro.berkeley.edu/~mwhite/darkmatte
r/bbn.html
Big Bang Nucleosynthesis
• The Universe's light-element abundance is another
important criterion by which the Big Bang hypothesis is
verified.
• It is now known that the elements observed in the
Universe were created in either one of two ways.
– Light elements (namely deuterium, helium, and lithium)
were produced in the first few minutes of the Big Bang.
– Elements heavier than helium are thought to have their
origins in the interiors of stars which formed much later in
the history of the Universe.
– Both theory and observation lead astronomers to believe
this to be the case.