Hubble again: a word of explanation

Let me begin my explanation of my last post by reminding you of something that I mentioned earlier. One thing that astronomers continually drum into us – except when they are talking about cosmology, that is – is the fact that all observations of the universe are conditioned by the speed of light. We do not see the universe as it is, but only as it used to be. Anything we say about the moon is already over a second out of date, about the sun eight minutes. Of the nearest star to us we can say nothing that is not already four-and-a-half years behind the times, of the nearest comparable external galaxy 700,000 years, of the furthest known galaxy some twenty-three thousand million years.Astronomers, in other words, are historians rather than geographers. Consequently anything they say about the universe as it is now – and especially about the extra-galactic universe – deserves to be treated with the gravest suspicion. For it pertains to metaphysics rather than to science. Like all the present-tense astronomical statements earlier in this chapter, it is a description of appearance, not reality. Every time an astronomer uses the present tense he is either speculating or indulging in superstition. It would be difficult to overstress the point. To represent deep-space astronomy as current fact is even less appropriate than treating Julius Caesar’s Gallic War as a description of present-day Europe. Any astronomer or cosmologist who invites us to regard statements about the extra-galactic universe as descriptions of present reality is asking us to accept the word of an expert who last looked at the evidence over 700,000 years ago.The consequences of these facts for Hubble’s theories are, to say the least, considerable. For it means that you cannot, on the basis of the observed redshifts, say that the universe is even expanding, let alone that the furthest galaxies are receding from us at ever-increasing speeds. To look out into space is also to look backwards in time, and there is no way, as Einstein himself pointed out, in which you can divorce the one from the other. Time declines to stand still while you look, refuses to oblige by providing a steady platform for your observations.And so all that you can say on the basis of Hubble’s interpretation of galactic redshifts is that the remotest galaxies used to be receding from us proportionally faster than the nearer galaxies were doing more recently. Think about that for a moment. It is a complicated statement. And it admits of almost any interpretation. What it actually means is a matter of probabilities rather than certainties. It could mean that Hubble was right, and we are living in a steadily-expanding universe. Equally (since the statement fails to compare like with like), it could be squared with the conviction that the universe’s expansion is either speeding up or slowing down. If, in other words, we could see both the remoter and the nearer galaxies at the same moment in time, we might very well find that their red­shifts were not, after all, directly proportional. Indeed, in view of the enormous time-lag since we last saw any of them, it could even be argued that the universe has long since stopped expanding and gone into reverse.True, these last two possibilities are unlikely if Newton’s laws of motion continue to apply to whole galaxies in deep space, and if Hubble was correct in assuming that extra-galactic redshifts are Doppler-effects indicating known speeds of recession, rather than Einstein-effects merely indicating relative motion in any direction (see next chapter). But then neither conclusion is by any means foregone. A universe that can start in an unexplained Big Bang can as easily end in an unexplained Big Slurp. Moreover, there is a not-inconsiderable astronomical lobby which nowadays insists that Hubble was wrong. American astronomer Halton Arp, working at the Hale Observatories, long ago amassed a vast amount of photographic evidence showing con­clusively that numerous external galaxies and other extra-galactic ob­jects with wildly differing redshifts were in fact physically associated with each other – whether gravitationally or otherwise – and must therefore lie in the same general area of space. V. A. Ambartsumian and his colleagues produced similar evidence in the former USSR.But why is this such an astronomical bombshell? Well, it has to mean, for a start, that extra-galactic redshifts are not, after all, reliable indicators of distance. The basic tool of cosmologists for at least the last seventy years has to be abandoned. And this in turn throws doubt either on the reliability of redshifts as indicators of recession, or on the whole concept of the expanding universe – or, indeed, on both. If, after all, the redshifts indicate speed of recession, then the anomalous objects are not where they ought to be in a uniformly expanding universe (in which case the whole Big Bang idea starts to look decidedly wobbly). If, on the other hand, the universe is expanding uniformly, then the redshifts are not reliable indicators of speed of recession. And if the redshifts are not reliable indicators of speed of recession, then the whole concept of the expanding universe falls flat on its face.Needless to say, Arp’s efforts have been greeted with much righteous anger within the astronomical establishment. He has been professionally ostracised, branded as a heretic, virtually excom­municated. The very strength of feeling that characterises the opposition to his views suggests that what is at stake is not so much a rational doctrine as an article of faith. Dogma is being questioned, belief subjected to scrutiny. Part of the anger, indeed, may derive from sheer frustration at the prospect that man may have, after all, to abandon his cherished, absolutist beliefs and humbly acknowledge his imprisonment by the relativity of the senses. As astronomer Jesse Greenstein has put it, the discrediting of Hubble’s long-established redshift/recession/distance relation would be ‘worse than the fall of the Roman Empire’.Yet extra-galactic redshifts occur. What, then, can be causing them? Distance and recession may, despite Arp’s work, have at least a role to play. Gravity, too, can cause a redshift, as required under the terms of Einstein’s General Theory of Relativity (to which we shall be turning in the next chapter). So, under the same theory, can relative motion in any direction. Other forces and processes, too may be at work – even other sets of ‘natural laws’ – all of them as yet unknown to our probing instruments and certainly not encountered within the limited scale of our terrestrial experience.Following Hubble, the next major step in this over-all journey of discovery was undoubtedly the launch of the NASA Space Telescope – now known, unsurprisingly, as the Hubble Telescope – in 1990. Astronomers at the time had hopes that it might answer a good many of the unsolved questions, even if it posed at least as many new ones in the process (we have difficulty enough, after all, in making sense of what we have recently discovered about Jupiter and Saturn, which lie, relatively speaking, in our own planetary back yard). For this large instrument, operating at an altitude of 366 miles, and thus free of the Earth’s atmosphere, would be able to penetrate several times further out into the universe – and thus several times further back in time – than terrestrial optical telescopes can ever hope to do.The prospects at the time seemed somewhat overpowering. If, as seemed possible, the Space Telescope turned out to be able to see out a distance of fifteen thousand million light-years or more, then whatever it saw at that distance would appear as it was at or before the birth of the universe – on contemporary, Hubble-based calculations at least. Yet it would be seeing it ‘out there’, not ‘in here’. But then, turned around through 180o, it would be seeing it out there, too. The universe, in other words, would be seen already to have measured at least thirty thousand million light-years across at a time when it is supposed to have been only an infinitely small ‘primeval atom’, or even a mere gleam in its Creator’s eye. Consequently either our estimates of distance, or our estimates of the age of the universe – or, indeed, our general cosmology – would finally have to go. Again, if the telescope’s range were to extend out to rather more than three times that distance, and distant brightnesses continued to swim into view, it is possible – just possible – that all of them might turn out to be... our own galaxy. For Einstein’s General Theory (see next chapter) also predicts that, owing to the general curvature of space-time, light-rays too will eventually curve back on themselves.The thought is more than a little worrying, even though, as it happens, there turns out to be insufficient certainty as to exactly what the telescope is seeing at the limits of its vision to confirm it. For if electromagnetic radiations such as visible light do not travel consistently in straight lines (being bent, as seems to have been demonstrated, when they pass through gravitational fields), then we may be totally deluded about where things are in space in the first place. Which is merely the culmination of a long chapter of sad deceptions, and the virtual coup de grace to our cherished cosmological beliefs. For, thanks to the very nature of the light we use to look at it with, not only are we unsure of what has been happening to the remote universe in the past, unaware of what is going on there now, and thus incapable of anticipating what will happen to it in the future. We cannot even be certain that it is ‘there’ at all.And so what are we to conclude? Is the universe expanding or con­tracting, steady or evanescent, solid and eternal or merely an illusory flash in the pan?Alas, as we have seen, any answer that you, the astronomers or the cosmologists are likely to give is far more likely to partake of the nature of belief and mediaeval superstition than of actual, established fact.

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