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The Dilemma

Thus the familiar interpretation of red-shifts as velocity-shifts leads to strange and dubious conclusions; while the unknown, alternative interpretation leads to conclusions that seem plausible and even familiar. Theories may be revised, new information may alter the complexion of things, but meanwhile we face a rather serious dilemma. Some there are who stoutly maintain that the earth may well be older than the expansion of the universe. Others suggest that in those crowded, jostling yesterdays, the rhythm of events was faster than the rhythm of the spacious universe today; evolution then proceeded apace, and, into the faint surviving traces, we now misread the evidence of a great antiquity. Our knowledge is too meagre to estimate the value of such speculations, but they sound like special pleading, liked forced solutions of the difficulty. The fundamental question is the interpretation of red-shifts.



The two clusters reproduced in the plate are extremely remote and, consequently, rather inconspicuous. Their interest lies in the fact that they bracket the present range of the spectrograph.
a. The Boötes cluster, at 240 million light-years, has furnished the largest, reliably measured red-shift, dlambda / lambda = 0.1307, which corresponds with a velocity of recession of about 24,200 miles per second. The area reproduced in the plate is about 56 square minutes of arc (about 8 per cent. of the area of the full moon), and contains about one hundred nebulae, two-thirds of which are members of the cluster. The large nebula, N.G.C. 5672, is relatively near our own system but happens to lie in the direction of the cluster.
b. The Hydra cluster, 5' north and 2.7' east of N.G.C. 2716, appears considerably fainter than the Boötes cluster because, although it is only slightly more remote, it lies in lower galactic latitude (+ 30°) and is more affected by local obscuration. Attempts to measure the red-shift in the Hydra cluster have hitherto failed. The reproduction, greatly enlarged from the original negative, shows about 70 nebulae in an area of 22 square minutes of arc.

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