Chapter#3 ~Astrophysics & Milky Way Galaxy: Part#1 prepared by Huriye Gürsel

Modern Picture of Cosmology

Modern Picture of Cosmology

Key Characteristic of Scientists THEY LOVE MYSTERIES!! The excitement to learn about the universe is their motivation for further research!!

The most amazing & mysterious thing... ... the stuff that you can’t see!!

DARK MATTER The mysterious stuff that dominates the universe! for further understanding ~ Einstein’s Equations!

Einstein’s Theory of General Relativity 1916 – GR FIRST theory of NOT ONLY how objects move through space, but also HOW SPACE ITSELF COULD EXPAND, CONTRACT & CURVE!

Einstein’s Equation Demonstration #1...

Matter cosmologists classify matter into two categories; slow moving and fast moving. Slow moving particles are particles that do not move at the speed of light. For fast moving particles (speed of light), as the universe expands their wavelength changes. For example, a blue photon will become a red photon, so the actual energy of every fast moving particle will decrease as the universe expands. Cosmologists call this a decrease in radiation energy.

Einstein’s Equation Gravity pulls & never pushes! Stars & galaxies pulled together! What to do..?

Expansion of the Universe “Added small repulsive force to the empty space!” ~ so small that it would not affect Newton’s laws which described beautifully the motion of planets around the Sun!

The Cosmological Term You would never measure it in the Solar System! However, it could build off on the scale of galaxies and hold the galaxies apart!

Expansion of the Universe “Having added the cosmological term, I have saved my theory!!!” Hmmmm.... Are you sure, Albert?!

Expansion of the Universe In 1929, Edwin Hubble (lawyer  astronomer) The universe is expanding uniformly in all directions!!!!

BIG QUESTION...

Expansion of the Universe If the universe is expanding, does that imply we are at the center of the universe??

Expansion of the Universe Demonstration #2... Workshop 3!

Expansion of the Universe You will see what Hubble had seen! The galaxies that are twice as far have moved twice the distance... It does NOT matter which galaxy you choose! Perspective#1: Everywhere is center of the universe! Perspective#2: Nowhere is center of the universe! DOESN’T MATTER! CONCLUSION: THE UNIVERSE IS EXPANDING!

Friedmann Equation describes the expansion of the Universe, and is therefore the most important equation in cosmology. one of the routine tasks for a working cosmologist is solving this equation under different assumptions concerning the material content of the Universe.

Expansion of the Universe Expansion of the Universe BIG BANG THEORY

Here comes the discussion... You are free to consider Big Bang; to validate your beliefs regarding an intelligent design or, to track backwards in time without the necessity of an initiator The path you choose to follow will depend on your personal beliefs, however; regardless of what you say, the Big Bang has happened! The universe is the way it is whether we like it or not!

How Do We Know Universe is Expanding? Doppler Effect!

Doppler Effect Galaxies are more and more red-shifted the further they are away from us! That’s how we know their velocities.. But, how about their distances? How can we know the distance from them, without actually going there?

STANDARD CANDLE METHOD A standard candle is an astronomical object that has a known absolute magnitude. They are extremely important to astronomers since by measuring the apparent magnitude of the object we can determine its distance Type Ia supernovae classed as standard candles, but in reality they are more standardisible candles since they do not all have the same peak brightness. However, the differences in their peak luminosities are correlated with how quickly the light curve declines after maximum light via the luminosity-decline rate relation, and they can be made into standard candles by correcting for this effect.

One of the embarassments of COSMOLOGY Hubble’s Original Observation, 1929: Universe ~1.5 billion years old Earth ~older ! He was NOT a bad astronomer! He just did NOT have good standard candles!

Now, we have great standard candles! Supernovae are transient objects. They appear suddenly as a bright star (that can outshine an entire galaxy) at a random position in the sky, and fade relatively quickly never to be seen again. For this reason they are difficult objects to find and study, and astronomers have now established several supernova searches dedicated to locating new supernovae and obtaining rapid and extensive follow-up observations of these objects. With such rapid follow-up, Type Ia supernovae have become one of the primary distance indicators in astronomy, helping to tie down the Hubble constant and revealing that the Universe is, in fact, accelerating. Now we can calculate expansion rate with a 10% precision

Back to Einstein’s Equation... ...a small step for a mathematician! + ...a big step for a physicist!

Back to Einstein’s Equation... What could contribute a term like this?? NOTHING! This is nothing but the energy of nothing! What do you mean by nothing??

Sounds like philosophy! But it’s not... NOTHING IN SR + QM In physics, NOTHING ~ A boiling, bubbling brew of virtual particles that are popping in and out of existence in a time scale so short that you cannot see them! Sounds like philosophy! But it’s not...

Empty Space Animation

Virtual Particles If we can’t measure them directly, how do we know that they exist? Casimir Effect Empty space inside a proton 90% of mass of the proton comes from the empty space between quarks !

QED The empty space is responsible for 90% of your mass! ONE OF THE BEST COMPARISONS BETWEEN THEORY AND EXPERIMENT IN SCIENCE: 10 DECIMAL POINTS IN QED USING VIRTUAL PARTICLES HOW CAN WE WEIGH THE UNIVERSE?

Weighing the Universe (we can use gravity Weighing the Universe (we can use gravity!) Curvature of Universe’s spacetime How universe will end!

Demonstration #3

Which Universe We Live in? Open Universe: expand forever... Closed Universe: expand, stop & recollapse in a Big Crunch... Flat Universe: expand and slow down and never gonna stop...

Gravitational Lenses Mass can act like a lens and magnify things and split images. Work backwards and figure out how much mass is required to obtain that image! (GR)

(Cosmic natural selection) Flat Universe The total energy of the Universe is precisely ZERO! Gravitational energy –ve Dark energy +ve (Cosmic natural selection) Quantum fluctuations can create a Universe... We are more insignificant than we think!

Summary Cosmological Principle: the place we occupy in the Universe is in no way special. The main mysteries lies within the stuff we CANNOT see! Age of the Universe = 13.72 billion years A flat universe  E = 0