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Home , Shape of the universe

Spring 2019 OLLI Courses • Understanding the Night Sky (3 lectures) – constellations, lunar phases, eclipses, planets – Aristotle, Copernicus, Galileo, Kepler • Observing the Night Sky (1 lecture) – staff member from Cherry Springs State Park – description of stargazing from Cherry Springs Let There Be Light: The Origin and Fate of the

• origin • contents • structure, size, shape • fate Looking into the Past The is very fast, but it is finite. As a result, it takes time for light to travel from a distant object and reach Earth, and the light collected by a telescope today shows an image of the object in the past. Objects that are farther away are seen as they existed farther back in time.

Time in past when light emitted

Present time when light received Which distance to use? Since light takes a finite time to reach us, and Earth and distant objects move during that time, the distance between Earth and those objects changes during the time that light travels to Earth.

distance when light emitted

distance today

These 2 distances are nearly the same for nearby galaxies (millions of light years), but they differ a lot for distant galaxies (billions of light years). So astronomers instead use lookback time for distant galaxies, which is how long the light received today has been traveling. The is the portion of the universe close enough so that light from it has had enough time to reach us since the Universe was born. What is the size of the observable universe?

What is the distance today of the most distant stuff we can see? In 1965, the radio afterglow from the was detected across the entire sky Age of universe = 400,000 years

42 million light years

Matter that will Matter that produced the become Milky Way microwave we detect now Age of universe = 1 billion years

Expansion of universe carries newborn, irregular galaxies away from each other Age of universe = today

46 billion light years

Detection of microwave Present form of the matter that photons in the Milky produced the microwave Way today photons we see today The Size of the Universe The microwave background radiation that we see today was produced shortly after the Big Bang by material that was only 36 million light years from our position in the universe, and yet it took 13 billion years to arrive at our location because of the expansion of the universe. 42 million light years after Big Bang: our location Now: CMB seen today 46 billion light years

The matter that produced the microwave photons that we see today is now 46 billion light years away, probably in the form of a galaxy. So the current diameter of the observable universe is 92 billion light years. Beyond the Observable Universe

Because the universe has expanded faster than the speed of light, some areas of the universe have been pulled beyond our light horizon, and are outside of our observable universe. Beyond the Observable Universe If we wait long enough, light will eventually reach us from some of the areas currently outside of our observable universe. But other areas are too far away for their light to ever catch up and reach us as the universe expands. Those areas will always remain outside of our observable universe.

Theories of suggest that the true size of the universe may be 1026 times larger than our observable universe, or 1037 light years. And it’s still expanding, so it will grow even larger! • A universe has a certain number of dimensions, or directions of movement • A universe has a certain shape or • A universe can be finite or infinite, depending on the shape • A universe has no edge or boundary, even if it is finite • A universe has no point within it that is the center

Is our universe one of many in a ? Matter exerts gravity, and gravity distorts Possible shapes for the universe Possible shapes for the universe what you see what you see what you see

The Shape of the Observable Universe As light travels through the universe, its path will follow the of space.

As a result, the apparent size of an object from our point of view is affected by the shape of the universe. We can determine this shape by measuring the sizes of clumps in the microwave background. By doing so, we find that the observable universe is flat. Why is the observable universe flat? Why is the observable universe flat? There are an infinite number of possible shapes for closed and open (i.e., infinite number of values of W<1 and W>1), but only one flat shape (W=1). So why do we happen to live in a flat universe? The theory of inflation is able to explain why: Because of inflation, the universe has expanded far beyond our observable universe. As a result, regardless of the true shape of the universe, it will appear nearly flat within our much smaller observable universe. We’ll never be able to measure the true shape of the universe as a whole.

observable universe inflation entire universe Let There Be Light: The Origin and Fate of the Universe

• origin • contents • structure, size, shape • fate The Fate of the Universe

Will the Universe expand forever?

Or will it stop expanding and collapse (a )? The Fate of the Universe If a baseball is thrown upward, it slows down because of the Earth’s gravity Similarly, the expansion of the universe should slow down because of the gravity of the matter in the universe

now

past The Deceleration of the Universe For either of the possible fates (bound or unbound), we expect that the expansion was faster in the past and slower now. As a result, the Hubble relation should bend upward for the most distant galaxies.

now past

1.5 3 (billion light years) To measure the expansion rate of the universe in the past, and thus determine if it is slowing as expected, the Hubble Telescope observed very distant galaxies Accelerating Expansion In 1998, Type Ia supernovae were used to measure distances for some of the most distant galaxies. When were measured for these galaxies, it was found that the universe was expanding more slowly in the distant past than now. The expansion of the universe is accelerating!

now past

1.5 3 (billion light years) But instead of finding this:

now

past The Hubble data showed that the universe expanded slower in the past than it does now

now

past

The expansion is accelerating! This is analogous to a baseball that accelerates as it moves upward from the ground The accelerating expansion indicates the existence of a repulsive force in the universe (anti-gravity), which is called

Dark energy is the dominant component of the mass and energy in the universe The influence of dark energy is related to the amount of space in the universe, so as the universe continues to expand, dark energy becomes increasingly dominant

Remaining Unknowns/Mysteries • What are the size and shape of the entire universe? • Will the expansion of the universe continue to accelerate forever? • Does our universe exist within a multiverse? • What are and dark energy? From Here to Eternity The Five Ages of the Universe: Inside the Physics of Eternity by Adams & Laughlin

• After 100 trillion years, there won’t be enough remaining gas for making new stars, and the last stars will have died. • The remaining matter consists of brown dwarfs, white dwarfs, black holes, and a little gas and dust. • A few new stars are made by the collision and merger of brown dwarfs. At any given time, there will be 2-3 stars in the entire Milky Way made in this way. • Black holes continue to grow by accreting any matter that comes too close. • The Milky Way disintegrates as its stars interact with each other and are kicked into intergalactic space. From Here to Eternity • After 1040 years, all protons and neutrons have decayed into smaller elementary particles. The only remaining matter consists of these particles and black holes. • After 10100 years, all black holes have evaporated and disappeared. The universe now contains only photons, electrons, , and other elementary particles. 1040=10000000000000000000000000 000000000000000 years 10100=1000000000000000000000000 00000000000000000000000000000 00000000000000000000000000000 000000000000000000 years The Hubble Deep Field To detect very distant galaxies, the Hubble Space Telescope stared at a small patch of sky for an entire week.

In 1929, Hubble discovered that more distant galaxies have higher velocities away from us velocity

distance X

Intensity - ray UV Hubble Space Visible Telescope Wavelength Infrared Radio X

Intensity - ray UV Hubble Space Visible Telescope Wavelength Infrared Radio X

Intensity - ray UV Hubble Space Visible Telescope Wavelength Infrared Radio X

Intensity - ray UV Visible Wavelength James Webb Space Telescope Infrared Radio