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The Hot Big Bang
Meet George Gamow
"Gamow was fantastic in
his ideas. He was right,
he was wrong. More
often wrong than right.
Always interesting;…
…and when his idea was
not wrong it was not only
right, it was new.”
Some Serious Science
Gamow asked (in the 1930s):
Where do the heavy elements come from?
You know the answer! They are created in massive stars:
 elements that are less massive than iron form during the
stable lifetimes of such stars
 elements that are more massive than iron form during
supernova events
But that understanding came later.
So Gamow Speculated
(before we understood stellar evolution)
Where could it be hot and dense enough to
cook up the heavy elements?
Answer: in the dense early universe – if it
had been hot.
The Ylem
With that motivation, Gamow suggested a hot
origin to the universe, in what he called the
‘ylem’ – a ‘cosmic egg’. (The word comes
from ancient Latin and Greek words for matter.)
Remember that this would have occupied all
space, with no ‘outside.’ Do not visualize a hot
blob sitting in a vast emptiness!
It’s Time to Reconsider
the Grenade Analogy
We explored the analogy to a
grenade to understand the
calculation of the time
since an explosion. I said
then that the analogy was
a very poor one.
It’s time now to tell you
why.
One Reason
A grenade explodes into pre-existing space that
surrounds it. The fragments move through
that space.
But the universe has no surrounding space into
which material moves. New, expanding space
appears everywhere ‘between the galaxies’
and carries the material with it.
There is not, never was, and never will be any
‘outside’to the universe.
The Second Reason…
A grenade expands because it gets very hot at the
centre (thanks to the rapid chemical reactions of the
explosive material in its core).
This creates a huge outward pressure, so the grenade
fractures and explodes into the surrounding lowerdensity space.
By contrast, the universal expansion requires no heat.
The expansion simply ‘is’.
The Name ‘Big Bang’
is Utterly Misleading
Fred Hoyle coined the term
‘Big Bang’ in a derisive way
– he didn’t believe in it!
But the term caught on, and
we still refer to the “Hot Big
Bang.“ Unfortunately, it
conjurs up misleading images
of a bomb exploding (noisily!).
It’s Not a Huge ‘Kablooie’
as it is so often depicted
(often with sound effects!)
So Please Remember…
The present expansion of the universe does not
necessarily imply that it started hot!
Gamow’s idea was imaginative speculation, intended
to solve the problem of heavy element formation.
On the other hand, we should not rule out the
possibility that it might have been hot. So Gamow’s
speculation was certainly worth considering.
His Idea
Thermonuclear reactions would take place in the early
moments, perhaps building up all the heavy elements.
It Doesn’t Work!
The rapid expansion dilutes the gas (the density
drops as the particles move farther apart), and
the temperature also drops. Any thermonuclear
reactions would quickly die down.
In fact, it’s fairly easy to show that the reactions
would not last long enough to create much in
the way of heavy elements
So Gamow’s imaginative idea was untenable.
But Not a Complete Failure!
We now know that Gamow was partly right! Most of the
helium and some light elements were indeed formed in
the early universe. (We will return to this in a bit.)
Still, Imagine the
Circumstances…
…if the early universe had been extremely hot. There
would have been:


rapidly-moving particles, in a fantastically dense
plasma; and
a ‘sea’ of energetic radiation everywhere.
But the material would have been so dense that it
would be opaque. (Radiation would not get far!)
With the
Passage of
Time, the
Temperature
Would Fall
Think of the temperature as a measure of the highly
energetic motion of the particles, or the nature of light
present – not in human terms of ‘how hot it would feel!’
These are unimaginably high temperatures.
As the Expansion Continues
The density drops, the freely-moving electrons get
captured by the protons --- and the radiation is now
able to flow unimpeded, like when a fog dissipates.
The universe becomes ‘transparent.’
Consequently
If we look around, we should find vestiges of that
radiation just reaching us now, after flowing
through space unimpeded for billions of years.
Moreover, the Cosmological Principle means that
this radiation should be uniform in all directions,
coming in from all sides.
So why is the sky not bright everywhere?
Remember the Redshift
The continual‘stretching’ of space means that the light
just reaching us now has been redshifted to very long
wavelengths (low energies).
So-called ‘relic radiation’ actually is now reaching us from
billions of light years away, after flowing through
space for billions of years!
In that sense, then, the sky around us truly is ‘bright
everywhere’ – just not at the wavelengths to which
the human eye is sensitive!
Gamow Actually Predicted This!
He noted that we should be
in a ‘bath’ of radiation, as
though sitting in an oven at
a very low temperature.
(His estimate: about 10
degrees above absolute
zero.)
It would have looked much
hotter at earlier stages.
This Was Untestable!
At the time of Gamow’s speculations, here was no
technology to search for the background radiation.
Moreover, as we came to understand the details of
thermonuclear reactions in stars, Gamow was
proven wrong about the origin of the heaviest
elements
For both these reasons, his work was dismissed
and forgotten about.
A Couple of Decades Later
In the 1960s:


Dicke (Princeton) thought again about a hot
early universe (but not to explain heavy
elements). Amazingly, he did not know about
Gamow’s earlier work and predictions!
He suggested that Peebles and Wilkinson search
for the radiation (now feasible)
Meet Jim Peebles
On A Recent Visit
Scooped!
Penzias and Wilson, Nobel Laureates
The CMBR
(Cosmic Microwave Background Radiation)
Proof of a hot early universe!
Improved Observations
Soon Followed
And Better Still From Space
The ‘dots’ are observations; the line is from
theory.
This is a Very Low Temperature
It’s like we are in an ‘oven’, immersed in a bath of
radiant energy at a temperature of just under 3K
(very close to Gamow’s prediction).
The universe was clearly hot in its earliest phases.
Gamow was right to suggest that possibility, even
if (in fact) it did not lead to his proposed result of
creating all the heavy elements.
It’s Not Absolutely Uniform
[it would be astonishing if it were!]
We see a ‘dipole’ – that is, the radiation from one side of
the sky has a spectrum that is a little ‘hotter’ than that
from the other side, owing to the Doppler shift and the fact
that the Earth has its own ‘peculiar’ (individual) motion
through the large-scale distribution of matter.
As We Look
Out, We Are
Looking Back
in Time
Further Vindication for Gamow:
Cosmic Nucleosynthesis
We now know where the H and He came from!
Consider The Role of Light
At one stage in the early universe, light (that is,
the enormous density and energy of the
radiation) was more important dynamically than
matter.
Moreover, at one stage, that’s essentially all there
was. In a very real sense, the matter we see
now ‘crystallized out’ from the enormous
radiation field.
The early universe was ’radiation dominated’
How Things Change:
A Succinct Representation
And again:
Cosmic
Evolution
Creation Stories
Light, sometimes in the form of a specific Sun god,
plays a significant role in creation stories from
many cultures and societies. This is of course
understandable, given the importance of light
(especially that of the Sun) for our existence on
Earth.
(You can explore many of these on the web; there
are both commonalities and striking differences
over many representations.)
In the Beginning…
Haydn’s
“Creation”
Oratorio
http://www.physics.queensu.ca/~hanes/A102-Movies/CreationMusic.mp4
https://www.youtube.com/watch?v=l07oRR4u-rk
- scroll to the 9m 30s mark