Sean Carroll

Sean Carroll is an American cosmologist who wrote From Eternity to Here and ‘Dark Energy and the Preposterous Universe’.

Quotes by Sean Carroll in Time One

It’s possible, of course, that general relativity is not the correct theory of gravity on cosmological scales ….

[T]he number of grains of sand on all the Earth’s beaches is only about 10^20.

For the first time in the history of science, we have at least a chance of putting together a sensible theory of time and the evolution of the universe.

… we still require an explanation for why the acceleration began recently.

[A]t early times the vacuum energy was negligible in comparison to matter and radiation, while at late times matter and radiation are negligible. There is only a brief epoch of the universe’s history during which it would be possible to witness the transition from domination by one type of component to another. … It seems remarkable that we live during the short transitional period between these two eras.

[W]hy are the matter and vacuum energy densities approximately equal today (the coincidence problem)?

Inflation has a lot going for it, but it makes the need for a theory of initial conditions even more pressing.

The state of the early universe was not chosen randomly among all possible states. Everyone in the world who has thought about the problem agrees with that. What they don’t agree on is why the early universe was so special―what is the mechanism that put it in that state?

… might be a few million times as massive as the Sun – big compared to any individual star, but still small compared to the galaxy. But it will continue to grow, sweeping up whatever unfortunate stars happen to fall into it.If we wait long enough – and now we’re talking 10100 years or so – even the supermassive black holes at the centers of galaxies will evaporate.

If our understanding of the fundamental, microscopic laws of nature is correct, we can specify the state of the universe at any time, and from there derive both the past and the future.

To this day, scientists haven’t yet determined to anyone’s satisfaction whether the universe will continue to evolve forever, or whether it will eventually settle into a placid state of equilibrium.

Concepts like “time” are not handed to us unambiguously by the outside world but are invented by human beings trying to make sense of the universe.

The arrow of time … is not a feature of the underlying laws of physics, at least as far as we know.