The universe is believed to be 13.8 billion years old and the observable universe stretches as far away from us as light can travel in the time since the universe was born. As such, you might assume that the observable universe stretches only 13.8 billion light-years in every direction. But because the universe is constantly expanding, this isn't the case.
When we observe a distant galaxy or star, we are seeing where it was when it first emitted the light. But by the time the light reaches us, the galaxy or star is much farther away than it was when we saw it.
Using cosmic microwave background radiation, scientists can work out how fast the universe is expanding and, on the basis of the rate being constant, the observable universe has been calculated to stretch 46.6 billion light-years in all directions.
Crewed spaceships, like Apollo, reach speeds of around 39,400 km/h (24,500 mph). At that constant speed, it would take around 27 thousand years to travel one lightyear.
There are estimated to be between 10^78 and 10^82 atoms in the observable universe. This is a vast number, often described as between ten quadrillion vigintillion and one hundred thousand quadrillion vigintillion.
An average 70 kg (150 lb) human body contains approximately 7 × 10^27 atoms. This is equivalent to 7 billion billion billion atoms. These atoms are primarily composed of hydrogen, oxygen, carbon, and nitrogen.
Atons are made up of subatomic particles including protons, neutrons, and electrons, as well as smaller particles like quarks and leptons. Quarks and leptons are currently considered elementary particles, meaning they are not known to be composed of smaller particles.
So here we are, back at those electrons that stop all matter from touching.