Hawking simplifies challenges in physics


AS was mentioned in my last article, I will start on some book reviews, which may also include books that I bought during Adelaide’s Writers’ Week.
For this and next week though, I will review two books by theoretical physicists.
I am of the view that the books, which were written for the non-science-trained reader, can be enjoyed by most people, as well as those interested in what sort of challenges are currently puzzling researchers in theoretical physics.
Physics, by the way, is a branch of physical science that studies energy and matter and the forces and fields that affect them.

Another book by Hawking
This week’s book is A Briefer History of Time, authored by popular theoretical physicist Stephen Hawking and Leonard Mlodinow.
Hawking passed away in 2018. He is the one who suffered from a motor-neurone disease and moved around in his wheelchair and gave speeches using a speech-generating device.
He was for a long time Lucasian professor of mathematics at Cambridge. Mlodinow, who partnered with Hawking in writing this book, is an American theoretical physicist, and has taught at the California Institute of Technology.
(For convenience and to save space, from here on I will cite Hawking as the author of the book instead of Hawking and Mlodinow.)
The book was published in 2005 and has 154 pages.
It also has index pages where the reader can use to refer to specific concepts mentioned in the book.
Additionally, it has five glossary pages where terms and words (like special relativity, quark or singularity) are briefly defined, hence making it easier for anyone to check for important words and their meanings.
A Briefer History of Time is a follow-up to Hawking’s first book A Brief History of Time which was published in 1988, was a bestseller and sold more than 25 million copies.
A Briefer History of Time includes up-to-date research findings and other details that may not have been included in the first book.
(I have two copies of Hawking’s first book and the one I am reviewing was borrowed from The University of Adelaide’s library.)

Development of physics described
There are 12 chapters in the book, with the last being the conclusion.
In the book, Hawking describes theories proposed by famous thinkers and scientists like Ptolemy, Aristotle, Copernicus, Newton, Einstein and other scientists who had a part in laying the foundations of physics, as we know it today.
The book informs the reader of experiments that researchers did and in the process discovered new theories in physics, or supported theories proposed by scientists or thinkers of those days.
It also tells us how some theories were proved wrong and discarded.
In reading the book, a reader will appreciate the development of physics (and science in general) and the methods utilised.
It also states what a scientific theory is, as opposed to theories that may be proposed in other non-science disciplines.

Details of the content
Hawking starts the book saying people over the ages have tried to make sense of the world around them and came up with models, which may seem absurd and laughable to many of us today. But then, we must understand they had not yet developed their mathematics and science.
He says that today though we are fortunate because “we have powerful tools: mathematics and the scientific method, and technological tools like computers and telescopes”.
Hawking also mentions the light-year, a very important distance when it comes to talking about distances in space, particularly when describing distances between us and different star systems or galaxies.
The light-year (which has a speed of 300,000 km/s) is the distance it takes for light to travel in one year, which is 9,500,000,000,000 km.
He also states that Proxima Centauri being the closest star to our Solar System is about 4 light-years away. (That means, the light that we see from Proxima Centauri, in the constellation of Centaurus, actually left it about 4 years ago. That was the concept that amazed me when I first read a book on astronomy when I was in Grade 12. The space that separated us from the stars we see in the night is immense, or astronomical.)
Then Hawking discusses the world of Aristotle and Ptolemy, the Greek mathematician and astronomer who proposed the earth-centred model (Ptolemaic model) where the sun and the other planets in the Solar System revolved around the earth.
We have since discarded that model for the sun-centred model (Copernican model), which sadly was not accepted for a long time by those in authority, those in the Church as well as in government.

Defining a scientific theory
In chapter 3, Hawking explains clearly what a scientific theory is.
He states: “A theory is a good theory if it satisfies two requirements. It must accurately describe a class of observations on the basis of a model that contains only a few arbitrary elements, and it must make predictions about the results of future observations.”
He also adds that “any physics theory is provisional, in the sense that it is only a hypothesis: you can never prove it … you can disprove a theory if by finding even a single observation that disagrees with the predictions of the theory”.
The scientific theory in that sense is different to theories in other disciplines, where people can argue for or against a theory without experimental data, or a mathematical model that can show time and again to support what is observable in nature.

The late Stephen Hawking, a theoretical physicist who popularised advanced topics in physics for the general reader. – Pictures borrowed

Take Newton’s theory of gravity, which we normally refer to it as Newton’s law of gravity.
The reason why it is still an accepted theory is because it predicts the fall of objects – also the rate at which they would fall from any height, provided that no external forces exist.
Then in chapter 5, Hawking touches on the topic of relativity.
Studies in that topic began to show that time was not absolute as was thought by Newton. This was a new concept that was developed gradually. In line with that it was argued that time can be different to two different observers.
An event that occurs, and as seen by two different people, person A and person B, who are travelling at different speeds would not seem to occur at the same time. This may not be observed if they were travelling at speeds we are used to though.
When we are dealing with speeds that are closer to the speed of light (the fastest speed ever), the time at which the event occurred for person A will not be the same as that of person B.
If person A had observed an event that took up a period of equals 2 minutes, person B’s record of the time duration could actually be 5 minutes, depending on their relative speeds to the location of the event.
It would seem as if time had stretched, or had dilated, for person B.
That is where modern physicists, like Albert Einstein, come in. They proposed new theories that explained what was observed, theories that explained physical phenomena that Newtonian laws or physics could not.
(Such theories are learned by physics students in their senior years in university. They are interesting because the concepts have been tested to be true despite us not capable of observing them in daily activities here on earth.)
One can observe such laws in action when viewing the very small world of atoms or the very big world of stars and galaxies, where the speeds of objects can be closer to the speed of light.
Einstein also proposed time as the fourth dimension to the three (length, width, height) that were already used to describe the position of an object in space. He put forward the concept of space-time and explained gravity in a different way to how Newton did.
In the book, Hawking says that “our biological clocks are affected by these changes in the flow of time”, and he discusses a favourite textbook example about the twin paradox.
Hawking mentions the case where there were two identical twins and twin A went on a long trip in a spaceship that travelled at a speed that is closer to the speed of light, while twin B remained on earth.
If they were to meet again, twin B would have aged more than twin A. (This is an application of what is referred to as time dilation in physics, where two different clocks carried by the twins would record different times, with one greater than the other.)
The big challenge remains
There are many interesting concepts or theories mentioned in the book, as well as bits of information on scientists that contributed to what we accept today as scientific knowledge.
Towards the end of the book, Hawking brings up the big challenge that is still present in physics.
Up until now, quantum theory is used to describe what happens in the micro world, the world of atoms and sub-atomic particles. On the other hand, relativity (as Einstein’s theory of special relativity and theory of general relativity) can adequately describe what happens in the macro world, the world of the stars, galaxies, black holes and other gigantic objects in space.
The challenge that remains is for physicists to find a theory to unite the two main worlds in physics.
String theory, which has been studied and hailed by some physicists, tries to explain phenomena observed in terms of 10 or more dimensions, as opposed to just four dimensions (as in space-time).
Hawking explains in the book that string theory has some faults. (I will not go into those. It is better that you read about that yourself.)
I am of the view that any educated person who may not have a background in science will understand a fair bit of the topics discussed in A Briefer History of Time.
Science students, particularly physics students in high school or university, will find the book very interesting and they may actually review concepts like Newton’s laws of motion, relative velocities and gravitation as well as forces in relativity and quantum theory.
If you do not have a science background and still want to understand more about what Hawking has shared in this book, I suggest you read the book, make notes and spend time with a physics or mathematics graduate to ask questions on concepts that you may not understand.

Next week: Physicist Richard A Mueller talks about time

One thought on “Hawking simplifies challenges in physics

  • The solution proposed by these scientists for the experiment of the twin paradox is based on acceleration. But the same experiment can be done without the use of acceleration. Here’s how it can be done:

    1. The return voyage of the spacecraft to Earth is not necessary, as at the end of the voyage we can place an observer who is motionless in relation to Earth. The reason is that the result of comparing the spaceship and remote observer clocks will be the same as the result of comparing the spacecraft and Earth clocks, as the clocks of stationary observers are always synchronized.

    2. In order for the spacecraft to start its journey it must first be accelerated. The spacecraft will then stabilize its speed. The experiment can begin at just that time, synchronizing the spaceship clock with that of Earth. It does not matter what the spacecraft did before this synchronization, so its initial acceleration plays no role in the experiment.

    Based on these data, we can alternatively assume that the Earth and the distant observer are moving relative to the stationary spacecraft. This, combined with the absence of acceleration in the experiment can only justify one result: that the clocks of the spaceship, the remote observer and the Earth do not differ until the spacecraft reaches the remote observer. At that moment, the spacecraft photographs the remote observer’s watch and stops. The clock of the moving spaceship must coincide with the clock photographed and the comparison of the two clocks at the moment of immobilization of the spaceship can not be very different. So the spaceship clock is still in sync with the Earth clock.

    (Examining this argument in good faith and carefully, I can find no serious error)

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