Probing the Very Early Universe (Part III)


Apologies for the delay in this post, I had started writing this ages ago, it was taking me forever to get the images right, and when I thought I was done, I lost both the post and the images!! I lost the will to live.

Catch up with the saga: part I, part II

A Neat Solution, Inflation

In the early 1980s, physicists started to take note of a theory that seemed to hold all the answers. The theory, cutely called ‘Inflation’ by MITs Alan Guth, offers a neat solutions to The Three Paradoxes of the Universe. In this post I will attempt to explain what inflation is, when it happened, and how it works.

What is Inflation?

Inflation is basically the very rapid expansion of the universe, where two points move away from each other at the speed of light(1). This does not contradict the special theory of relativity, since at the time this happened, the universe was classically empty, only energy existed at this time.

When did it happen?

Hard to quantify too precisely, but we can take on board two bits of information from two different sources in order to give a ball-park figure on this. Inflation must obey the physical laws of nature, there is no escape, however we are not entirely sure what these laws looked like such a long time ago.

[Extra Reading] The origin of the fundamental laws of physics:

One of the fundamental ideas of physics is that all the physical forces that we see as independent today (i.e. the force of gravity is seen as independent of say the theory of electromagnetism), were actually all ‘united’ many years ago, when the energy of the universe was ‘free’ (i.e. not bounded by structure, like atoms and such). That is, billions of years ago, physicists think only one law of nature existed, and that as the universe grew and cooled, this one law subdivided into a few sub-laws of nature. If you’re a bioligist or are more comfortable with the ideas of biology, think of this evolution as a top down process, as opposed to biology’s bottom up approach to evolution. So if a physicist had come up with a theory for the origin and diversity of the species she would have imagined one super-being (not divine, just super, as in ‘super duper’) that then spawned lots of other species, who then spawned even more species! But this spawning of mutants was already encoded in the first super-being, i.e. all the DNA any animal/plant needed existed within the chromosomes of that first super-being, and the genes ‘came to life’ as it were in response to the environment. That is the basic idea of the unification and subsequent diversification of the laws of physics, with the environment being the temperature/size of the universe.

Now, the physics world has managed to unite all the fundamental forces… except for one: Gravity. But that is not what we’re talking about, we assume that gravity did somehow unite with the other forces, and generally, gravity appears after what is known as the Planck epoch. The Planck epoch defines a time when the early universe was only a Planck length in diameter. This Planck length is special, in that it defines the smallest size that we know how to analyse physically i.e. we have a theory of how things behave when they are very small, or very very close together, but not if they measure less than or are closer than a Planck length. Since inflation deals with the expansion of space time, it needs general relativity (aka gravity) in order to operate, so Inflation takes place after the appearance of gravity.

So as a first guess Inflation takes place at least billion billion billion billionth of a second after the Big Bang. But to be brutally honest, since the theory of inflation is still work on progress, then inflationary cosmologists also look at scenarios when inflation took place at or before the Plank time, that is: less than 10 million billion billion billion billionth of a second after the Big Bang.

The second bit of information we need is when did the contents of the Universe become dominated by radiation? That occurred about a 10 millionth of a second after the Big Bang, and we need the universe to have ‘settled down’ by this time, because our theories of what happened after this time (the `standard’ Big Bang evolution) hold up pretty well under scrutiny, and we dont want to change things too much.

So inflation took place between a billion billion billion billionth of second after the big bang and 10 millionth of a second after the Big Bang. This would seem pretty precise for most people, but remember in the early universe aLOT of stuff could have happened within this time, after the universe became radiation dominated it took only 3 minutes for the temperature to drop 999,999,999,999,999,999,900,000,000 degrees Celsius. So we may have nailed the epoch of inflation to a few millionth of a second, but that still leaves alot of room for uncertainty.

 

How does it work? i.e. how does it solve the Three Paradoxes of Cosmology

How inflation explains the causality, homogeneity and isotropy of the universe?

inflation1

This is a schematic diagram of the expansion of the universe. The figure on the left represents the standard big bang expansion, assuming only radiation and matter. The figure on the right represents big bang + inflation. To understand this diagram, you need to imagine that our universe is contained within the black lines, and that it grows as you follow the arrows.

Looking at the figure I have included (click on it for a better view), I have attempted to illustrate how the two different scenarios (Standard Big Bang vs. Inflation and Big Bang) expand. You need to imagine that our universe is contained within the two vertical black lines, so it grows as you follow the arrows.  Now, what we know of the age of the universe, and what we know about how radiation and matter (regular stuff) effect the rate of expansion, then it turns out that there were 50,000 parts of the universe not in causal contact. That is, the universe could not have been small enough for these parts to communicate. That is, 14 billion(ish) years ago, according to standard lore, the universe was made up of 50,000 independent regions. So why did these regions all evolve in the same way?

This is where inflation comes in, because inflation stretches the universe out in such a tiny amount of time (see previous section), it means that the universe could have started out much smaller than was actually thought, and expanded very quickly, all this without effecting the evolution of the universe from light to atoms to galaxies to us (i.e. Big Bang Nucleosynthesis). Referring back to the figure, the red and blue circles represent two regions in the universe, in the inflationary picture they start off very close to each other, so information gets shared between them, or more to the point the universe mixes and homogenizes

How does it solve the problem of the age of the universe? (or why isn’t it older?)

Since inflation causes the universe to grow to the size required by the theories which govern Big Bang Nucleosynthesis in a teeny fraction of a second, our theory of universal evolution now accounts for the age of the universe. We no longer need to add to the age of the universe to account for phenomena.

How does it solve the origin of structure? (or where did all this stuff come from?)

The answer to this one is quite involved, we need to look at how one gets inflation, i.e. what causes the universe to expand so rapidly? Once we answer this question, we discover that inflation also explains the origin of structure AND why it started expanding in the first place.. for next time though🙂

(1)this is one scenario, but the other one is too complicated to explain right now

Next up: Negative pressure, exotic particles, and the emergence of something out of nothing

14 Responses

  1. I really don’t know much about the inflation of the universe since we haven’t studied it, thanks anyway for your post, it explained a bit to me or at least made me more familiar to it.

    I am really looking forwards to the emergence of something out of nothing.

    btw, you haven’t answered my questions yet which are:
    How do we know were the center of the universe is, it was explained to me several times but never understood how the center can be anywhere in the universe.

    My second question was, according to the Quranic creationism, what did god create first, the earth or the heavens (stars)? and is that scientifically true?

  2. I am really dreading the next post in this series, am trying to think of ways to tackle the quantum to classical transition in laymans terms.. but I’ll cross that bridge when we get to it.

    But back to your questions, allow me to take a stab at the second question. I admit to avoiding it since I do not know all the verses in the quran which relate to the formation of the universe. But, I have consulted the Maurice Bucaille book which has compiled verses relating to scientific phenomena.

    In your previous comment you said that the Quran refers to the earth being created first. According to Bucaille people get this impression because in some verses the earth is mentioned before the heavens as in ‘the earth and the heavens’ or al-ard wa al-samawaat. However in chapter 21 verse 30 the following is said:

    “Do not the unbelievers see that the heavens and earth were fused and then we clove them asunder…”

    Bucaille then goes onto making an astronomical connection to this verse. he says:

    “science informs us that their [earth and sun] formation occured by a process of condensation of the primary nebula and then their seperation”

    now we turn to the quranic verse, in another verse (sura 41 v 11) the heaven is referred to as being in a state of ‘smoke’, or a gaseous substance.

    So in this case science and Islam are not at odds.

  3. oh and as for your first question, i think that might be a post in itself. I had not ignored you, I am just finding ways of explaining things.

  4. There is a verse that describes earth was like a smoke, and then it came together by the command of Allah. Even though I do not remember the verse verbatim.

    But I gather it’s very difficult to describe early universe without lack of rigor. It’s something that kind of haunts me. But something is better than nothing, whatdoyasay?

    • That is the verse I mentioned in my response. The verse and its ilk demonstrate that a factory style ‘creationism’ is not what went down, that the universe and what was in it was created by processes. Hence the lack of perceived rigour, which may be due to lack of understanding for all I know, is not one that haunts me, esp when taking into account that islam encourages Muslims/believers to look around and above them and ponder its origins.

  5. Thanks for your answer although I totally disagree with it.

  6. loolt, there is no benefit in trying to prove that Islam and Science and Islam are not at odds. That is a defensive position, and makes the point look weak.

    What do ya think?

    • I wasnt actually feeling defensive when I responded, I was trying to answer a question that I get alot in my line of work. Mostly people think that Science and Religion are at odds for some reason, this was my stab at addressing this question. What is important is that looking for processes by which the universe came to be in the state it is in is not at odds (well important for muslims anyway), and that we have to ponder how it all came about.

      • Hmm. I don’t know if you share my opinion, but it is my belief that modern pholosophy of science is strongly influenced by Islam.

        For example the Hadith about the honey (footnote). Or the repeated emphasis on observing and drawing conclusions and verification in Islamic jurisprudence.

        footnote: Once the prophet(SAW) took some honey and showed it to some Sahaba (I don’t remember who) and asked them “what is it?” All of them answered “honey, ya RasulAllah.” Only Ali tasted it and then said “it is honey, ya RasulAllah.” Upon which the Prophet said- “the one who tastes, knows.”

  7. sorry “Islam and Science”🙂

  8. […] Catch up with the saga: part I, part II, part III […]

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