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If the speed of light were half its actual value, would the universe have developed very differently? (continued)
Mike Follows
Sutton Coldfield, West Midlands, UK
If the speed of light were half its present value, the universe would probably be very different. The speed of light is deeply woven into modern physics – including relativity, electromagnetism, quantum theory and gravity – so changing it would affect everything from cosmic evolution to chemistry and possibly life itself.
A lower speed of light would alter the evolution of the cosmos. Light, gravity and other physical influences would propagate more slowly, changing not only the size of the observable universe at any given age, but potentially its development as well. The growth of structure in the early universe could unfold differently, affecting how matter clumped together under gravity.
Galaxies might therefore differ in size, shape and distribution, while stars could burn differently or fail to produce the heavier elements needed for planets and biology.
However, physicists are cautious about questions involving changes to the speed of light alone. In modern physics, the most physically meaningful quantities are often dimensionless constants – pure numerical ratios formed from combinations of well-known universal constants such as the speed of light, the electron charge and Planck’s constant. Because these ratios are independent of human measurement systems, they are generally regarded as more fundamentally physical than the individual constants themselves.
If the speed of light were lower while the other quantities remained fixed, the fine-structure constant would increase, making electromagnetism significantly stronger.
Atoms and chemistry would then change as well. Electrons would behave differently, altering chemical bonding and molecular structure. Relativistic effects already influence heavy elements: gold’s colour and mercury remaining liquid at room temperature both partly result from electrons moving at appreciable fractions of the speed of light. With stronger electromagnetic interactions, heavy elements could become chemically unrecognisable or unstable.
Complex molecules such as proteins and DNA might then struggle to form or remain stable. Since life depends on a delicate balance of physical forces, even modest changes to fundamental constants could disrupt the rich chemistry upon which biology depends.
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Even modest changes to fundamental constants could disrupt the rich chemistry upon which biology depends
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This connects with the anthropic principle. In its weak form, the principle states that the observable universe must possess properties compatible with the existence of observers. Some physicists extend this idea through multiverse theories, proposing that many universes with different physical constants may exist, and that we naturally find ourselves in one where the constants permit stable matter, complex chemistry and conscious life.
Quite possibly, a universe with half the present speed of light would never produce observers capable of posing the question in 91av.
Graham Smith
Melbourne, Australia
The universe would be a very different place if the speed of light were half its actual value. For example, the fusion process in stars releases energy proportional to the square of the speed of light, according to Albert Einstein’s most famous equation. Therefore, halving the speed of light would result in one-quarter of the energy release.
The heating due to the radioactive decay process in the centre of Earth would be similarly affected, so it is likely that the planet’s core would have cooled long ago. Thus, Earth’s magnetic field would have been seriously weakened, and our atmosphere more likely to be blown away by the solar wind… if our weakened sun could still generate a solar wind.
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