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Dark Matter and Dark Energy

Just because something is unknown does not make it unknowable

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Dark Energy Dominated Universe

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Total Mass/Density of the Universe

Dark Energy makes up 72% of the total mass-energy density of the universe. The other dominant contributor is Dark Matter, and a small amount is due to atoms or baryonic matter.

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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.

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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.

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Dark EnergyThis 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.

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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..

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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.

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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.

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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.

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Dark Energy

• What is known is that astronomers/astrophysicists need more and better data.

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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.

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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.

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Dark Matter

• Dark matter is sometimes described as the scaffolding of the universe on which all visible bodies (suns, galaxies, planets, etc.) are built.

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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/darkmatter/bbn.html

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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.