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A Different Approach to Cosmology : Hoyle, Burbridge and Narlikar - Part 1
01/02/07
A Different Approach to Cosmology : Hoyle, Burbridge and Narlikar - Part 1
There's a lot to this book, so I'm simply going to have to split the review of the book into a few pieces.
There are a few main themes to this book: to provide some recent history of cosmology, to give some interesting astronomical observations, to explain Quasi-Steady State Cosmology or QSSC, to explain some mainstream cosmology, and to tie QSSC into modern observations.
The three authors are no slouches in the astronomy field. That's not to say that they're right, of course. Hoyle in a nutshell:
This is one more reason for paying attention to Sir Fred. Even when he was wrong he was extremely interesting.
The cosmology history part of this book is well worth the price alone. It's hard to find good resources of cosmology history. What little you do find trumpets one or two things, and then Hubble's career just peaks in 1929 when he co-wrote a famous paper that turned out to inspire Big Bang cosmology, and he, and pretty much everyone else, is never heard of again. What did everyone do in the intervening decades?
The book opens in the pre-30's, in an age where it turned out that many nebulae were actually islands of stars unto themselves. It is in this age that Einstein formulated his theory of General Relativity.
The book is pretty good for interjecting the mathematics that people were using at the time. If you haven't seen General Relativity equations, for example, the book lists them.
Einstein thought, like Newton, that the universe was static. Modelling the universe as a static universe containing dust, on average, he got nonsensical solutions:
...where S is the 'radius' of the universe.
It was this that purportedly led Einstein to insert the famous cosmological constant 'lambda', giving the equations above as:
From his revised equation:
Willem de Sitter, though, solved Einstein's field equations in another manner, with an empty universe without a cosmological constant, showing that Einstein's solution was not unique. To wit, Einstein's universe was matter without motion, de Sitter's was motion without matter.
It was in this era (the 20's) that a more general means of encompassing both Einstein and de Sitter's universes was formulated, now dubbed FLRW universes after the contributors, Friedmann, Lemaître, Robertson and Walker. It is this set of equations that are still being used some 80 years later.
One of the important constants in the FLRW equations is called k, and it determines what kind of universe is being dealt with. It can have one of three values.
If k = +1, then the universe is closed; theoretically, if you travelled far enough in one direction in a k = +1 universe, you could arrive back where you started. This was the most popular thought for most of the 20th century. If you imagined space itself flattened like in a drawing, the universe would be a sphere.
If k = 0, the universe is flat. This means that space itself has no curvature. It implies infinite physical boundaries.
If k = -1, the universe is open. This means that space curves away from itself. It's also a lot harder to picture; some diagrams show it as a "saddle" shape, which does it little justice.
Hubble discovered the redshift/apparent velocity relation in 1929. It is almost always this work that is referred to by Big Bang theory and theorists. This relation is now known as Hubble's Law, and has a value, Ho which relates the distance and apparent velocity.
The tasks set for the 30's were:
- Measure Ho better
- Predict expansion slowdown (a slowdown in the expansion of the Big Bang has been predicted until relatively recently
- Find out whether k is -1, 0 or +1 (still unresolved)
Following chapters chart the course of theory and observation capability, attempts to measure the curvature of space, with a great smattering of math (though nothing remotely as difficult as the math required to even understand a few pages of Penrose's masterpiece), and some estimates and observations.
Hubble may have gotten the Nobel prize, but given that the award is never given posthumously, many deserving candidates are cheated of the prize by time. He died in 1953, and the note at the bottom of a graph, "no recession factor", indicates that he still opined that redshift was not due to any actual velocity.
One thing that started rearing its ugly head was the age paradox (still an ongoing concern; see here, here - it's probably called something different these days). In any model of the universe at the time (and up to the present day), measurements of Ho indicate that the universe should be young. The problem is, given knowledge of stellar processes (a fascinating science in its own right), there is not enough time for many stars to form, never mind galaxies or larger structures. The very original measurement of Hubble's and Humason, 558 km/(s*Mpc) gave an age of the universe younger than the oldest rocks, so it could not be right. It went down in value to around 70, which is a commonly-used value today, though Sandage used some arguably good techniques that reduce that value to 55-58.
(The lower the value, the older the universe can be, generally, but there are good reasons for thinking that, say, 30 is way too low a value)
Most work in the modern age is to figure a way around the age paradox, and 13.7 billion years, far from being "set", is considered a minimum (e.g. Stephen Hawkings' own estimates are a few billion higher)
The 50's and see us being introduced to two of the authors (G. Burbridge and Hoyle), and to see the interesting factionism that went on in the day, in the decades past the 1948 introduction of the 200" Palomar telescope, and the introduction of radio astronomy. Ryle's group in Britain, according to Hoyle's account, was secretive and hammered out differences of opinion internally so that a unified face could be presented.
Optical identification of radio sources led to the discovery of many sources with lobes on either side, implying a magnetic field or jets. The discovery of quasars was soon to follow.
The 60's saw fresh inventions help out with observation, bringing in image-tube spectrographs for taking spectrums, and CCDs, the forerunners of those in digital cameras, for imaging. This extended the reach of telescopes yet again.
There is a section here in the book where it talks about using Hubble relations and how there is one caveat: if you are looking back in time, you would be looking back to a prior era, and galactic/stellar luminosity, etc., may have evolved significantly in the interim. The book gives four equations to plug an evolution function into, depending on the value of qo, the 'deceleration parameter'.
Well, that's the book up to chapter 6. I'm slowing down in this second reading to try to understand the book more thoroughly, since I was a bit confused on first reading. The next set of chapters talk about Big Bang Theory, Steady State Theory (the original), and the sorts of observations they purport to explain, and why.
Until next time...
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