The Cosmos: From the Big Bang to Black Holes
The universe explained with real numbers and real reasoning, and always with how we know it.
For curious adults who want more than pretty pictures and never got on with the equations. Nothing harder than multiplying and dividing: you will work out a light-year, why an orbit is a fall that never lands, and what a 1% dip in a star's light means. Every claim comes with the measurement behind it, and where the answer is still unknown, the course says so.
By the end you can
- Read cosmic distances and times correctly, and explain why looking far away is looking into the past
- Explain how a star lives and dies, and use its mass to predict whether it leaves a white dwarf, a neutron star or a black hole
- Say how we actually know each big claim: parallax, spectra, redshift, the microwave background, gravitational waves
- Tell the measured parts of modern cosmology apart from the parts that are still open questions
Scale and light
- How big is space?
Turn cosmic distances into something you can picture: read a light-year correctly, shrink the Sun to a football, and see why looking far away means looking into the past.
- Light, the messenger
Almost everything we know about the universe arrived as light. Learn to read it: what a spectrum is, how dark lines reveal what a star is made of, and how a shift in those lines shows motion.
- Gravity, the sculptor
Gravity is the weakest force and still shapes everything big. See why an orbit is a fall that never lands, why large bodies are round, and how a nearly smooth universe turned into stars and galaxies.
The lives of stars
- How a star is born and shines
Follow a cold gas cloud as gravity turns it into a star, see what fusion really is and why it is not burning, and learn the balance that keeps the Sun steady for billions of years.
- How stars die
One number decides how a star ends: the mass it started with. Follow the Sun to its white dwarf, see why an iron core collapses in under a second, and learn how we check any of it.
- We are stardust
The universe began with almost nothing but hydrogen and helium. See where the carbon, oxygen, calcium and iron in your body were actually made, and how anyone could possibly check that.
Extreme objects
- Neutron stars and pulsars
A star's core squeezed into the size of a city, spinning hundreds of times a second. See what that does to density, spin and magnetism, and why some of them tick like clocks.
- Black holes
Work out for yourself why a small enough ball of mass traps its own light, learn what an event horizon is and is not, and see the four independent ways we know black holes are really there.
- Spacetime: Einstein's idea
Gravity is not a pull but a shape. See how mass curves spacetime, why clocks run slower where gravity is stronger, and why your phone would be kilometres wrong without the correction.
The universe as a whole
- The Big Bang and its evidence
Three separate measurements point the same way: the universe was once hot and dense. Learn what expansion really means, why there is no centre, and how the oldest light in existence was found by accident.
- Dark matter, dark energy and the expanding universe
Galaxies spin too fast and the expansion is speeding up. See the measurements that force both conclusions, what has already been ruled out, and exactly where the honest answer is still 'we don't know'.
- Other worlds
How more than five thousand planets around other stars were found without ever seeing one, what the habitable zone does and does not mean, and an honest look at the question of life.
Keep it, don't just read it
Pathwise brings each idea back just before you'd forget it, with a quick question. Free on Android and on the web, in English and Persian.