Gravity by Brian Clegg (book review).

January 23, 2013 | By | 6 Replies More

  Gravity. Can’t see it. Can’t live without it. It keeps us on the Earth and if you fall from a great height, you’ll fall at the same speed as anything else on this planet.

Brian Clegg’s book ‘Gravity’ explores the history of its discovery from Galileo through to Newton and beyond. It’s also rather interesting how Clegg puts to death certain myths about these early scientists and if might stop you looking at an apple tree and wonder why only Newton spotted the phenomenon of falling. The exploration of quantum mechanics might seem complicated for some of you but please persist with that chapter when you get there because it will give you some insight into where gravity starts from.


For Science Fiction readers and writers, chapter eleven, ‘Cavorite Returns’ should be required reading for you to ponder over. For instance, if you want to maintain an Earth-type gravity, then you really shouldn’t travel faster than 9.81m(32 ft)/second/second which means you’d never get far within a generation.

I’ve never come across the precise definition difference between speed and velocity like this before. Speed is scalar, the number you’re moving at. Velocity combines speed with direction. Remember that when you’re using both words as I’m pretty sure I’ve confused this in the past myself.

Clegg explains a lot of forms of what appears to be anti-gravity that isn’t, ranging from gas balloon buoyancies to strong magnet propulsion and super-conductivity.

One thing I would take issue with him over is the assertion that stopping gravity, objects would travel at nearly the speed of light. Granted some of the lower grade SF writers might have gotten that wrong but he ought to read Isaac Asimov’s short story ‘The Billiard Ball’ (it’s in ‘Asimov’s Mysteries’ for those who haven’t read it). Essentially, the universe is expanding and if you stopped moving relative to it, then the rest of the universe would move away from you. For those watching on the planet, you would have effectively sped away at a high velocity, although it’s not you but them in the expanding universe doing so. Not perhaps at the speed of light but it’s easy to see why it’s described that way. It would be a great way to travel but you would never be able to catch up with the expanding universe.

Things I learnt and occasionally puzzled over.

In space, a plant’s roots don’t know which was to go. That made me think a little. If they’re in zero gee and encased in a plastic bubble, then all it would need is the occasional water and nutrients injected.

The information on page 7 about how the body would change if you were born in zero gee should be required reading for all SF writers and you would be dooming such people to never come down to earth (sic).

If you ever wondered how science started off by being called a philosophy, then you can blame Aristotle because he would debate how things work than prove it by experimenting and it took a long time to shake that off, which we owe to Galileo. In many respects, Aristotle sounds a lot like those people we have around today who let they fears think for them than proof.

The event horizon of a black hole is just under ten miles. That one I would like to see proved. You can probably use angular momentum, that’s being in orbit, to stop falling into a singularity but I’d wonder at the astronaut who would put that to the test.

With the four basic forces of the universe, I’m still puzzling why no one looks at why the weak and strong nuclear forces aren’t considered being closer together.

The most important lesson I learnt relates to the sun. We all know that if it explodes, it would take eight minutes before the event destroyed us. As such, we would still be in orbit around the sun until then indicating that the effects of gravity take the same eight minutes to reach us. If that doesn’t make you ponder, then read this book to find out more.

As you can tell from my responses above, I found this an interesting book. As the uses of gravity is something that comes up a lot in Science Fiction, this should be a book all of us need to read, if for no other reason than to use accurate facts.

GF Willmetts

(pub: Duckworth Overlook. 322 indexed page hardback. Price: £14.99 (US). ISBN: 978-0-71564-360-0)

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Category: Books, Science

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About UncleGeoff

Geoff Willmetts has been editor at SFCrowsnest for some 21 plus years now, showing a versatility and knowledge in not only Science Fiction, but also the sciences and arts, all of which has been displayed here through editorials, reviews, articles and stories. With the latter, he has been running a short story series under the title of ‘Psi-Kicks’
If you want to contribute to SFCrowsnest, read the guidelines and show him what you can do. If it isn’t usable, he spends as much time telling you what the problems is as he would with material he accepts. This is largely how he got called an Uncle, as in Dutch Uncle. He’s not actually Dutch but hails from the west country in the UK.

Comments (6)

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  1. Brian Clegg says:

    Thank you for your kind words, but I do want to pick you up on one point. As written it sounds as if I suggested that if you ‘stopped gravity’ you would fly off at the speed of light. I was actually pointing out this error in a 1950s popular engineering magazine that said this.

    However, I’m afraid your assertion isn’t quite right either. You say ‘For those watching on the planet, you would have effectively sped away at a high velocity, although it’s not you but them in the expanding universe doing so. Not perhaps at the speed of light but it’s easy to see why it’s described that way.’ This isn’t the case.

    Gravity doesn’t stop the universe expanding. Because it’s space itself that is expanding they are totally separate effects. At a local level, the expansion of the universe is not noticeable – you certainly wouldn’t speed away at high velocity. The rate of expansion is proportional to the distance the object is away from you – for two proximate bodies, like you and the planet it is effectively zero.

  2. UncleGeoff says:

    Hello Brian

    I never said you said objects would move away at the speed of light.

    Did you read the Asimov story?? It really addresses what happens when you stop relative inertiam, which effectively cancels gravity. From the observer pov, you would just vanish but really it is the observer moving away in the expanding universe. I didn’t say it was at the speed of light, just the relative speed of the expanding universe, which is 7*10^-10/sedonc/second which would still look like you’ve vanished, providing that there was no obstacle in the way to splat upon. That is still pretty fast and it’s gravity which keeps us here.


    • Brian Clegg says:

      Thanks Geoff –
      I know that wasn’t your intention, but ‘One thing I would take issue with him over is the assertion that stopping gravity, objects would travel at the speed of light.’ makes it sound as if I made that assertion. Just a wording issue.

      The expanding universe doesn’t have a ‘speed’ – the whole point of Hubble’s law is that the further something is away, the faster the expansion of the universe makes it move with respect to you. To objects that are next to each other are moving away from each other at effectively zero speed. Turning off gravity would not make you move just because the universe was expanding. I think what Asimov was saying is that if you could turn off inertia (which is there is no conceivable way of doing), you would immediately stop moving against some inertial zero frame of reference (whatever that is – Einstein said there was no unique frame of reference), while the Earth would continue, so you would fly away from it. This is a totally different concept.

  3. UncleGeoff says:

    Hello Brian

    Page 266-7. Which does go back to what I was saying about inertia. Cutting off gravity from an object, which interprets as cutting off its basic immobile inertia, the object would seemingly whizz off which you place at 170,000 mps. The speed of light is 186,000 mps, so all I’m missing is a ‘nearly’. At that velocity, you aren’t going to be able to tell that much of a difference. I agree with you it would be astounding if if could be done but one would only have to hope that what was ever in the bubble kept everything else out and kept everything in at something like Earth-normal (especially if playing with such forces in the first places that was taken into account) it might even be survivable, assuming that they decelerated at a much slower rate. Even turned off for a split-second, you’d be long gone.

    You’re quite right, as a vector force, the expanding universe has a velocity not a speed. Turning off or reduce inertia would reduce your velocity relative to the expanding universe and if you were the object, you’d see the Earth fly off in one direction and if you were on Earth, the person affected would effectively have vanished.

    Isn’t inertia an effect of gravity? If you’re not falling, then you stay where you are but that’s relative motionless as the Earth is still moving in the expanding universe.


    • Brian Clegg says:

      Sorry, this is going to have to be the last comment, but the quick answer is no, inertia has nothing to do with gravity. Inertia is why if something is moving it will keep moving with the same velocity unless a force is applied to it. You have inertia whether or not you are in a gravitational field – the only difference is that under gravity your straight line goes through curved spacetime, so you can end up in an orbit.

  4. UncleGeoff says:

    Hello Brian

    No one said you have to answer in the same day.

    I’ll leave you something to ponder: All I said was that changing inertia is the only thing I could think of that could defy gravity.


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