dr martin hendry university of glasgow. dark energy cold dark matter atoms state of the universe –...
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Dr Martin HendryUniversity of Glasgow
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Dark Energy
Cold Dark Matter
Ato
ms
State of the Universe – Nov 2003
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The Runaway The Runaway UniverseUniverseDr Martin HendryDept of Physics and AstronomyUniversity of Glasgow
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Cosmology – the study of the Universe as a whole:
• Origin
• Evolution
• Eventual Fate
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Galileo Galilei:1564 – 1642 AD
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Galileo Galilei:1564 – 1642 AD
“I have observed the nature and the material of the Milky Way. With the aid of the telescope this has been scrutinized so directly and with such ocular certainty that all the disputes which have vexed philosophers through so many ages have been resolved, and we are at last freed from wordy debates about it.
The galaxy is, in fact, nothing but a collection of innumerable stars grouped together in clusters. Upon whatever part of it the telescope is directed, a vast crowd of stars is immediately presented to view. Many of them are rather large and quite bright, while the number of smaller ones is quite beyond calculation.”
from The Starry Messenger (1610)
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The stars are VERY far away. The nearest star (after the Sun) is about 40 million million km from the Earth. It takes light more than 4 years to cross this distance (travelling at a speed of 300,000 km per second)
If the Earth-Sun distance were the width of this screen, the nearest star would be in Paris !!!
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Measuring Astronomical Distances: Parallax
Earth in July
Earth in JanuarySun
Nearby star
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Measuring Astronomical Distances: Parallax
Earth in July
Earth in JanuarySun
Nearby star
View from the Earth in January
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Measuring Astronomical Distances: Parallax
Earth in July
Earth in JanuarySun
Nearby star
View from the Earth in January
View from the Earth in July
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Measuring Astronomical Distances: Parallax
View from the Earth in January
View from the Earth in July
Even the nearest star shows a parallax shift of only 1/2000th the width of the full Moon
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Cepheid Variables: Cosmic Yardsticks
Henrietta Leavitt1908-1912
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The nature of the nebulae?…
Early 20th Century
Gas clouds within the Milky Way, or Island Universes?….
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The Great Debate, 1920
Shapley vs Curtisat the National Academy of Sciences
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The Great Debate, 1920
Shapley vs Curtis
Shapley argues successfully that the nebulae are within the Milky Way
at the National Academy of Sciences
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1922: Hubble finds Cepheids in the Great Nebula in Andromeda
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Hubble measured distances to dozens of nearby nebulae
Even the nearest, in Andromeda, was
millions of light years distant
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Hubble also measured the shift in colour, or wavelength, of the light from distant galaxies.
Galaxy
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Hubble also measured the shift in colour, or wavelength, of the light from distant galaxies.
Galaxy
Laboratory
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Hubble also measured the shift in colour, or wavelength, of the light from distant galaxies.
Galaxy
Laboratory
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Hubble’s Law: 1922Hubble’s Law: 1922
Distant galaxies are receding from us with a velocity proportional to their distance
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‘Recession of the Nebulae’ caused not by the motion of galaxies through space, but the expansion of space itself between the galaxies
Hubble’s Interpretation
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How fast is the Universe expanding?How fast is the Universe expanding?
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Principal difficulty has been local distortions in ‘Hubble flow’
e.g. spectrum of M31 is blueshifted
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Galaxies are clustered
Structure in the Universe assembled by gravity
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Galaxies are clustered
Structure in the Universe assembled by gravity
Locally, gravity sufficient to overcome cosmic expansion
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Galaxies are clustered
Structure in the Universe assembled by gravity
Locally, gravity sufficient to overcome cosmic expansion
On larger scales, expansion diluted: galaxies have peculiar velocity on top of Hubble velocity
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Main local distortion due to Virgo cluster
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Problem:
Need to determine H0 from remote galaxies, where peculiar motions are less important….
….but….
We cannot use primary distance indicators to measure their distance
Need Distance Ladder!!
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HST has ‘bypassed’ one stage of the Distance Ladder, by observing Cepheids beyond the Local Group of galaxies
This has dramatically improved measurements of H0
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Virgo Cluster galaxyM100, 60 million light years distant…..
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HST Key Project, led by Wendy FreedmanMeasure Cepheid distances to ~30 nearby galaxies,
Link Cepheids to Secondary distance indicators
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Must ensure that remote galaxy data are free from Selection Effects
e.g. intrinsically brighter or bigger?…
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Must ensure that remote galaxy data are free from Selection Effects
e.g. intrinsically brighter or bigger?…
Malmquist Bias
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Must ensure that remote galaxy data are free from Selection Effects
e.g. intrinsically brighter or bigger?…
Malmquist Bias
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Will the Universe continue Will the Universe continue to expand forever?to expand forever?
To find out we need to compare the expansion rate now with the expansion rate in the distant past…
Is the Universe speeding up or slowing down?
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Answer depends on the geometry of the Universe
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Answer depends on the geometry of the Universe
Closed
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Answer depends on the geometry of the Universe
Closed Open
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Answer depends on the geometry of the Universe
Closed Open Flat
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We can measure this using Supernovae and the background radiation
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Geometry of the Universe affects the relationship between distance and redshift of the supernovae
Closed Open Flat
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We can measure this using Supernovae and the background radiation
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Early Universe too hot for neutral atoms
Free electrons scattered light (as in a fog)
After 300,000 years, cool enough for atoms; fog clears!
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Background radiation predicted in 1950s and 1960s by Gamov, Dicke, Peebles.
Discovered in 1965 by Penzias and Wilson
Arno Penzias and Robert Wilson
Robert Dicke
Jim Peebles
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Cosmic Background Explorer (CoBE), launched 1989
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CoBE map of temperature across the sky
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CoBE map of temperature across the sky
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CMBR ‘ripples’ are the seeds of today’s galaxies
Galaxy formation is highly sensitive to the pattern, or power spectrum, of CMBR temperature ripples
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Position of first peak sensitive probe of thegeometry of the Universe
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Hot off the press!…
Microwave Anisotropy Probe
First year WMAP results published Tuesday 11th Feb
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First year WMAP results published Tuesday 11th Feb
From Bennett et al (2003)
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Position of first peak sensitive probe of thegeometry of the Universe
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Answer depends on the geometry of the Universe
Closed Open Flat
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Results:
The expansion is accelerating
The geometry of the Universe is FLAT
The Universe will continue to expand indefinitely
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What is driving the cosmic acceleration?…What is driving the cosmic acceleration?…