What these observations and others like them suggest is that only around 5 per cent of the universe’s mass is made of the matter we can touch with our hands and witness with our eyes and instruments. This is the matter of stone, water, bone, metal and brain, the matter of which the ammoniacal storms of Jupiter and the rubble rings of Saturn are made. Astronomers call this ‘baryonic matter’, because the overwhelming share of its mass is due to protons and neutrons, known to physicists as ‘baryons’. A little over 68 per cent of the universe’s mass is presumed to be made of ‘dark energy’, an
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