# The Horizon Problem and Inflation

Friends, today we will talk about a problem that plagued the big bang theory of the universe for decades and the strange solution that physicists proposed to solve it.

In an earlier VERITAS we had studied about the cosmic background radiation. This is the radiation left by the big bang itself. It is the cosmic radiation “smoke” that tells us that a loooong time back an explosion ( the big bang ) happened. So if you point sensitive equipment to any part of the sky you will “hear” a dim background noise. Its source is something 14 billion light years away from us. IF you calculate the temperature at which matter would radiate like this you would find that it is about 4 Kelvin( 4 degrees above absolute Zero). And remember that when you look farther into the Universe you are looking backwards in time. Since light takes 14 billion years to come from the cosmic background radiation spot to us that means that we are looking 14 billion years back in time!!!

Look towards the east. You will find 4K cosmic bacground radiation 14 billion light years away. Look towards the west. You will find 4K cosmic background radiation 14 billion light years away. The cosmic background radiation(CBR)  looks exactly the same whether you look towards the east or towards the west. They seem to be in an thermal equilibrium with each other. How much is the distance between the two horizons? It is 28 billion light years! So the east and west horizon have not met for atleast 28 billion years. And what is the age of the Universe? 14 billion years! Isnt that weird?????!!!! If the CBR at the east and west horizon came from the same big bang then they have been separated by 28 billion light years. But our universe is only 14 billion years old. SInce nothing can travel faster than light this means that these two parts of the CBR have never interacted!!! We say that the CBR in the east lies outside the light horizon of the CBR in the west.

Similarly the CBR in the north lies outside the light horizon of the CBR in the south. Since all these parts of the CBRs have never interacted how come they are soo similar? How come they are at thermal equilibrium with each other? This is the Horizon problem.

Physicists hace come up with a very strange theory to explain this. They propose that within a minute of the big bang there was a HUGE expansion in the universe. We know that the universe is expanding at a particular rate.

But this expansion was not this normal expansion. It was A MUCH MUCH BIGGER expansion. It expanded much faster than light! It just blew up. It blew up by a factor of 10^50 ( 10 followed by 50

zeros) in a very very short time ( .000000000000000000000000000000000001  i.e 10^-32 second). So in a small fraction of a second the Universe just blew up in a huge way! This would not violate Special Relativity which says that nothing can move faster than light because space and time themselves were expanding. If inflation happened then the east and west CBRs are within the light horizon of each other. So they have interacted in the past( within the lifetime of the Universe) to reach the same temperature.

But if inflation is true then there is a stranger consequence: the observable universe ( the 28 billion light year diameter) is a very small portion of the complete universe. There is a huge amount of stuff outside this. It is outside our light horizon so we will never  be able to interact with it!

Not all Physicists believe in the inflation theory. SOme think that maybe the speed of light was much greater just after big bang than it is now and that would explain how these CBRs interacted within the lifetime of the universe.

But how do we verify these theories? We cannot experiment with the universe! Are we to just philosophise fruitlessly?

Friends, we exist for such a short time. And there is so much to learn. Would our lives finish without this thirst for knowledge quenched? And how does one quench this thirst for knowledge when we know how limited our tiny brains are???!!! I sometimes wish that there were a God. Then at least I would be able to ask him about the Universe. The human endeavour to search for truth, our Science, is too painful. How little we achieve through Science in our tiny lives!!!!!! If only we could ask God the questions. Without God life seems to be so useless and incomplete- a drop of water that will never reach the ocean.

Why cannot I be the one who sits in front of Krishna and Krishna says as he said to Arjuna: “I shall now declare unto you in full this knowledge, both phenomenal and numinous. This being known, nothing further shall remain for you to know.”

Why should I struggle endlessly with false knowledge, false books and a limited time on earth:

Study is like the heaven’s glorious sun

That will not be deep-search’d with saucy looks:

Small have continual plodders ever won

Save base authority from other’s books

These earthly godfathers of heaven’s lights

That give a name to every fixed star

Have no more profit of their shining lights

Than those that walk and wot not what they are.

Too much to know is to know nought but fame;

And every godfather can give a name.

Kanwar

|======================================================|

Go, wondrous creature! mount where Science guides:

Go, measure earth, weigh air, and state the tides:

Instruct the planets in what orbs to run,

Correct old time and regulate the Sun;

|======================================================|

# SUPERFLUIDITY

Friends, In today’s VERITAS we will talk about a strange phenomenon in Physics. We all know that we we lower the temperature to absolute zero(-273 degrees C or 0 Kelvin) all molecular motion stops. i.e the molecules in a body subjected to such low temperatures stop moving. At temperatures close to absolute zero we meet two strange super phenomenon : superconductivity and superfluidity.

Today we will talk about superfluidity.

All gases when cooled turn into liquids and when further cooled turn into solids. Helium is a strange gas. It cannot be converted into a solid. It can be cooled to attain a liquid form at

4.2 K ( 4.2 degrees above absolute zero). In 1937 the SOviet Physicist Kapitza was studying the properties of liquid Helium at temperatures below 4.2 K. At about 2.2 K it started changing into something else: not a solid but a crazy new kind of liquid- a superfluid.

At 2.2K Helium can flow in pipes without friction! i.e if it starts moving in a pipe it can go on forever. A normal liquid will slow down and stop eventually. But superfluid helium can go on forever.

A normal liquid stays in a jar with microscopic pores because its viscosity and surface tension prevent it from leaking through those microsopic pores. But there aint nothing stopping superfluid helium- it can, and it will leak even from microscopic pores. So you need special kinds of vessels to store liquid helium without leaking it.

In a normal liquid sound flows like a wave. A sound wave moves through a liquid faster than it does in air.  But in a normal liquid heat spreads slowly- it dissipates, it moves through conduction and convection. But a superfluid is a superconductor of heat! In a superfluid heat moves like a wave. So if we had a world filled with liquid helium we could transmit information using heat – heaters would act like loudspeakers and thermometers like a antennas!

Helium can behave like a superfluid because it is a boson.

A boson is a particle with  an integral value of spin(0,1,2 etc). These are different from fermions which have half integral values of spin(1/2, 3/2 etc). Fermions obey the Pauli’s exclusion principle- no two fermions can be in the same state. Bosons dont obey this principle- all bosons can be in the same state. So a superfluid is a situation where all molecules of the liquid are in the same state. They all have the same momentum. So if one molecule moves all of them move together.

So the molecules stick together and go everywhere together. There is no opposing motion or random motion( like it happens in a normal liquid)- – thus there is no friction!

The theory that explained superfluidity was first made by the great Soviet physicist Lev Landau in 1941. Lev Landau received the Nobel Prize for his theory in 1962.

Lev Landau was one of the greatest physicists of the 20th century. He was also a great teacher. He wrote a set of books with his assistant Lifschitz called ” The course of theoretical Physics”. This set of 9 books have become classics. Each one is beautifully written. I have read 4 of these and have been moved by their beautiful concise style and wonderful treatment.

Lets get back to superfluids. Can a superfluid be found in nature? Yes! Superfluids are found in neutron stars. A neutron star is one which is so dense that the star has been stripped of its electrons. It consists only of neulei of atoms. But a star is supposed to be hot! How come there can be a supercooled superfluid there? Well, supercooling is just one way of forming superfluids. If you press bosons close to each other using very high pressure they will come together to form a superfluid. And that is what happens in the superdense neutron star.

But a neutron is a fermion( has a spin of 1/2). So how come they can come together to form a superfluid? The reason for this is exactly the same reason that causes superconductivity( flow of electrons in wires without resistance). According to the BCS theory electrons sometimes form pairs known as Cooper pairs. In these pairs the two electrons have opposite spin. So the Cooper pair has a net spin of 0( which is integral). So though the electron is a fermion but the Cooper pairs of electrons is a boson and is thus capable of being all in the same state. Thus in a superconductor all electrons form pairs and all these pairs are in the same state- they have the same momentum and they all move together without friction. This is exactly what happens in a neutron star. The neutrons form pairs and these pairs are bosons capable of forming superfluids.

Friends, this is a beautiful world full of wonderful and strange things. But the beauty that we experience in every day life is very limited. We can only experience things with sizes from .1 to 100 metres in every day life. We can only experience temperatures from 0 to 50 degrees C. We can only experience the small portion of the universe that is near us. But the universe is soooo much bigger. How can we remain satisfied with so little beauty that we can experience with our senses. To experience much more beauty we have to use our mind, the method of science and the tool of mathematics. A scientist is the real lover of beauty. Ignite that love for beauty!

Kanwar

========================================================

Go, wondrous creature! mount where Science guides:

Go, measure earth, weigh air, and state the tides:

Instruct the planets in what orbs to run,

Correct old time and regulate the Sun;

|======================================================|