Lesson 1

1

The Big Bang

The Big Bang describes the universe's expansion from an early hot, dense state about 13.8 billion years ago. This lesson introduces that expansion and the evidence for it, including the movement of galaxies and the radiation left from the early universe.

Key Ideas

• Everything (space, time, matter) began with the Big Bang about 13.8 billion years ago.
• The Big Bang was not an explosion in space. It was the expansion OF space itself.
• We know it happened because galaxies are still moving apart and cosmic background radiation fills the universe.
• Time itself began at the Big Bang, so there was no 'before.'

Spines

• DK Science pg. 112-113
• Alternative: NASA’s What is the Big Bang (https://spaceplace.nasa.gov/big-bang/en/)

Vocabulary

• Universe: Everything that exists, including all matter, energy, space, and time taken together as a whole.
• Big Bang: The moment ~13.8 billion years ago when all of space, time, and energy began expanding from an incredibly hot, dense point.
• Expansion: The ongoing process by which space itself continues to stretch and grow, carrying galaxies farther apart.
• Energy: The ability to do work or cause change. The first moments of the universe were pure energy before matter even formed.
• Singularity: The tiny, unimaginably hot and dense point from which the universe began. Think of it this way: right now, the observable universe is about 93 billion light-years across. The singularity was smaller than an atom.
• Cosmic Background Radiation: Faint heat energy left over from the Big Bang that still fills the universe today. It's like the 'afterglow' of the Big Bang. Scientists discovered it by accident in 1965 and it became some of the strongest proof that the Big Bang really happened.

Discussion Questions

1. What was the universe like before the Big Bang?
   Sample Answer: “There was nothing, no planets, no stars, no space.”
2. Why was the Big Bang NOT like fireworks or an explosion?
   Sample Answer: “Because it wasn’t loud and it didn’t happen in just one place.”
3. What happened in the very first moments after the Big Bang began?
   Sample Answer: “Space got bigger, time started, and tiny bits of stuff moved around.”

Digging Deeper

1. What do scientists think the universe was like before the Big Bang?
   Sample Answer: Scientists are not sure. Some think there was no 'before' because time began at the Big Bang, so the question has no answer. Others wonder if our universe is one of many (multiverse theory), but this is still very speculative. Some think the universe may have 'bounced' from a previous universe that collapsed.
2. Why do scientists believe the universe is still expanding today?
   Sample Answer: Scientists see galaxies moving away from each other, like dots on a balloon getting farther apart as it inflates. They also notice red shift in light and leftover radiation from the Big Bang, called cosmic microwave background.
3. If you could witness the first moment of the Big Bang, what do you think you'd experience?
   Sample Answer: Answers will vary dramatically.