Prince Rahul's Key Ideas from Brief Answers to the Big Questions
by Stephen Hawking

• ….. was a star so massive that it had collapsed in on itself.
• It’s so massive that not even light can escape its gravity, which is why it’s almost perfectly black.
• It’s gravitational pull is so powerful, it warps and distorts not only light but also time.
• Black holes are formed when stars collapse by its own gravity.

• Stars supports itself against its own gravity through the creation of thermal pressure.
• Inside every star, a huge amount of energy is being generated through nuclear reactions (fusion) which convert hydrogen into helium.
• Eventually, a star will run out of nuclear fuel. When this happens, most stars draw all surrounding matter inward and contract to an infinitely dense, infinitely small point or singularity – this is the black hole.

• In nanoseconds, the universe went from an infinitely dense point ( maybe smaller than a proton ) to a rapidly expanding body which continues to grow today.
• Evidence supporting such a theory first appeared in 1965, with the discovery of faint background microwaves in space.
• These microwaves are likely leftover radiation from an initial “bang.”

• Most massive objects – like black holes – can warp space-time so violently that time itself stops.
• By following the “chain of causality” back to its furthest point, we can prove the Big Bang couldn’t have a cause because time didn’t exist.
• There was no time for a cause to exist in.🤯

• Hawking discovered that black holes release particles at a steady rate ( Hawking Radiation).
• His theory argues that space is filled with particles and antiparticles. They’re in a constant process of bonding, separating and then annihilating one another.
• The complex interaction of these pairs with black holes – particularly when partners are separated by the event horizon – causes black holes to lose mass, shrink and eventually disappear.

• Space and energy can materialise out of nothing. The laws of physics demand the existence of something called “negative energy.”

Imagine a man wants to build a hill , To make this hill he digs a hole in the ground and uses that soil to dig his hill.

But of course he’s not just making a hill—he’s also making a hole, a negative version of the hill.

Here, The Hole is negative energy and the hill is positive energy.

• Space itself is a vast store of negative energy. Enough to ensure that everything adds up to zero.
• The universe is like an enormous battery storing negative energy.
• It means that if the universe adds up to nothing, then we don’t need a God to create it.
• The universe is the ultimate free lunch.
• Positive energy is the matter which has mass.

1. The first is matter—stuff that has mass.
2. The second thing we need is energy.
3. The third thing we need to build a universe is space.

• Einstein realised that two of the main ingredients needed to make a universe—mass and energy—are basically the same thing.🤯
• His famous equation E = mc^2 simply means that mass can be thought of as a kind of energy, and vice versa.
• So instead of three ingredients, we can now say that the universe has just two: energy and space.

• The universe is a machine governed by principles or laws.
• The laws of nature are a description of how things actually work in the past, present and future.

Laplace argued that if we knew the positions and speeds of all the universe’s particles, we could calculate their future behavior.

But Heisenberg discovered that due to the way , light waves are packaged into discrete units called quanta, “you cannot measure both the speed and position of a particle simultaneously; the more accurately you measure one, the less accurately you can measure the other”. This rule became known as the uncertainty principle.

In quantum mechanics, particles do not possess well-defined positions and speeds. Rather, these values are represented by something called a wave function. 

A wave function is a set of numbers, each one representing a different point of space. The size of the wave function predicts the probability that the particle will be found in each point of space.

So, We can’t predict the future but we can make it :)

• Global warming might be Earth’s most immediate threat, but we also face a greater one: nuclear annihilation.
• Our planet could end up like the surface of Venus – a planet not known for its hospitable conditions (250 degree Celcius and evening showers of sulphuric acid).
• In the planet’s present state, it’s almost inevitable that either nuclear war or environmental disaster will devastate Earth in the next 1,000 years.
• By that point, though, humanity will hopefully have the technology to escape the planet and survive disaster.

………suggests that “computers can double their speed and capacity every 18 months. If our gadgets keep following Moore’s law, AI may surpass human intelligence within the next hundred years, making the possibility of a self-aware Skynet less remote.”

• It’s estimated that 20 percent of all stars have Earth-like planets orbiting them in the Goldilocks Zone . ( a region capable of sustaining life because it’s not too distant from its star to be an icy wasteland, but not close enough to fry its inhabitants)
• There are roughly 200 billion stars in our galaxy, the Milky Way. This potentially gives us forty billion Earth-like planets just in our cosmic neighborhood.
• Other lifeforms might not have been so lucky :)