The Big Bang
Three pieces of evidence for the origin of the universe
Do Now: Almost every galaxy we see is moving away from us. Does that mean Earth is at the center of the universe?
No! Observers in any galaxy would see the same thing: all the other galaxies moving away. Space itself is stretching, so there is no center. Try it below with “Make the target my home.”
Try It First
Press Expand. Click any galaxy to make it the target and see its spectrum.
The Big Idea
1. Redshift
Distant galaxies are moving away from us — and the farther they are, the faster they go. The universe is expanding.
2. Cosmic Microwave Background
A faint glow of microwaves fills the whole sky — the leftover heat of the early universe.
3. Composition
Ordinary matter is about ¾ hydrogen and ¼ helium — just what the Big Bang predicts.
Lessons
NYS P-12 Science Learning Standards: HS-ESS1-2 — Construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.
Evidence for the Big Bang
The Big Bang theory states that the universe began about 13.8 billion years ago in an extremely hot, dense state and has been expanding and cooling ever since. Scientists accept this theory because several independent lines of evidence support it.
Which set of observations provides evidence for the Big Bang theory?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. Light from distant galaxies is redshifted. What does this show?
C2. A hydrogen spectral line produced at 656 nm in the lab is observed at 689 nm in the light from a distant galaxy. For speeds much less than light, v = cΔλ ÷ λ. Substitute numerical values into this mathematical representation to determine the galaxy’s recession speed. Then calculate the speed.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. Place a check mark in three boxes to indicate statements that are consistent with the Big Bang theory.
C5. What is the cosmic microwave background (CMB)?
C6. A classmate says, “If the universe is expanding, then Earth, the Sun, and our galaxy must be getting bigger too.” Describe what is actually expanding, and identify the evidence astronomers use to show the expansion.