Vol. 18 No. 15 · 1 August 1996
pages 18-19 | 2808 words
Big Bang to Big Crunch
John Leslie
- The Nature of Space and Time by Stephen Hawking and Roger Penrose
Princeton, 141 pp, £16.95, May 1996, ISBN 0 691 03791 4
The Nature of Space and Time contains six lectures-three by Stephen Hawking, three by Roger Penrose – and a closing Hawking-Penrose debate. As Penrose indicates, it might be viewed as continuing the famous Bohr-Einstein exchange of some seventy years ago. Against the background of new cosmological theories, Hawking defends Bohr’s thesis that quantum theory has no radical incompleteness. Those who think it incomplete are wrongly treating its formulas as describing reality, rather than as predictive tools. Like Einstein, Penrose disagrees. Things then get somewhat tense. Hawking uses terms like ‘magic’ in dismissing theories which Penrose brought to the general public in The Emperor’s New Mind. Penrose throws some courteous cold water on the universe-creating mechanism made famous by Hawking’s A Brief History of Time.
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Letters
Vol. 18 No. 18 · 19 September 1996
From L.C. Laming
John Leslie, in his account of the Penrose/Hawking debate (LRB, 1 August), writes: ‘The limited speed of light restricts how much of the universe we can observe. There are regions so distant that no light from them could yet have reached us, during the roughly ten billion years since the Big Bang.’ I can believe that there are regions so distant that light leaving them now can never reach us (assuming continued expansion) but it is surely impossible that light did not traverse totally the much smaller universe of the remote past – unless, of course, even the early (but post-galaxy formation) expansion already exceeded light speed. Indeed, we are constantly being told that we are viewing extremely old galaxies having ages of approximately 90 percent of the age of the universe. This is often accompanied by a related anomaly, in that these objects are said to be N billion years old and N billion light years distant – the latter by implication now, which is patently not a valid equation. Could a cosmologist please explain?
L.C. Laming
Imperial College
Vol. 18 No. 20 · 17 October 1996
From John Leslie
Reacting to my account of the Hawking-Penrose debate, L.C. Laming (Letters, 19 September) asks how on earth there could be ‘regions so distant that no light from them could yet have reached us’. Surely, he suggests, light must have been able to ‘traverse totally the much smaller universe of the remote past’. The solution to Laming’s puzzle is that the cosmic expansion constantly added to the distance the light had to cross. Even an early separation of, say, one centimetre might still not have been bridged. Laming is right, though, to ask why so many people suggest that the N billion years of an observed region’s age must make it exactly N billion light years distant. The cosmic expansion does destroy that equation. Stumbling down Pike’s Peak with Don Page, a leading cosmologist, I asked him what the actual equation should be. He calculated it in his head – but it took him 15 minutes.
John Leslie
University of Guelph, Ontario
Vol. 18 No. 23 · 28 November 1996
From L.C. Laming
John Leslie is either trying a version of Zeno’s Paradox on us (Letters, 17 October) or, with respect, missing an important condition mentioned in my letter. I can well believe that the centimetre-sized universe was expanding during the super-inflation period (say from 10-43 to 10-35 secs) at rates well ahead of light-speed, but in referring to ‘early universe’ I did say ‘post-galaxy formation’, i.e. the universe at about one-tenth of its present age, since that is the universe from whose galactic inhabitants we are told we are now receiving the light. But from that stage to the present, the rates of furthest galactic recession have been presumably (a) never faster than they are now, and (b) at a snail’s pace compared to light-speed. Hence the question – why are ‘we’ only seeing them now?
L.C. Laming
Imperial College
