My dear daughter,
We should talk about cosmology.
So far, we know the Universe is approximately 13.7 billion years old. We know it from the microwave background radiation which is more or less uniform everywhere we look. Also from particle decay and the rate at which galaxies are moving apart. It is also possible to infer the age of the Universe from the age of the oldest and farthest galaxies we can see.
Our best theory so far is that there was a singularity 13.7 billion years ago, but that doesn’t necessarily mean the singularity was the beginning of the Universe, but it was the start of an inflated expansion era.
The size of the observable universe is actually larger than 13.7 billion light-years because there was also spatial expansion. Space expands faster than light.
From measuring the distance to distant quasars and supernovae, we know the Universe is still expanding at an accelerated rate.
The problem is, from the matter and energy density of the Universe we can observe, it shouldn’t be accelerating. Something is providing energy so every point in space continues to accelerate apart. They are calling it Dark Energy, in the absence of a better name.
There are many hypotheses to what Dark Energy could be, but there is no evidence so far to sustain any particular one. Soon after proposing General Relativity, Einstein added a constant to his equations, which he called the cosmological constant, to account for a stable Universe; he felt equilibrium should be the norm. Almost a hundred years later, scientists really discovered something is keeping the expansion going, similar to Einstein’s “arbitrary” constant.
Then there is also Dark Matter. From our observations, galaxies are spinning faster than they should, based on the amount of matter we can measure in them. So there should be some sort of hidden matter to account for the faster spinning. It interacts with normal matter only through gravity; it doesn’t interact with the electromagnetic force, so we can’t see it. Lacking a better name, scientists are calling it Dark Matter. It could be exotic particles, a different flavor of neutrino, matter from unreachable dimensions, etc.
The interesting fact is, either our measures are wrong or incomplete, or 95% of the Universe is made of things we can’t see – Dark Matter and Dark Energy.
Our physics could be wrong or incomplete too, but the Standard Model has prevailed after decades of tests. There is still the issue of incorporating gravity, but it’s a solid scientific theory.
Love,
Dad
Aspergers Dad 