Red-shift and the Big Bang
Red-shift (Separate Physics only)
When astronomers look at light from distant , the wavelengths are longer than expected. The light is shifted towards the red end of the spectrum. This is called .
- More distant galaxies show a bigger red-shift.
- This means distant galaxies are moving away from us, and the further away they are, the faster they are moving.
- So the universe is expanding.
Picture dots drawn on a balloon. As you blow it up, every dot moves away from every other, and dots further apart separate faster.
Common mistake
Red-shift doesn't mean galaxies look red. Their light is stretched to longer wavelengths.
Key terms
The Big Bang (Separate Physics only)
If the universe is expanding now, it must have been smaller in the past. Red-shift is evidence for the : the universe began from a very small region that was extremely hot and dense, and has been expanding ever since.
Scientists estimate the universe is about 13.8 billion years old.
Key terms
Open questions (Separate Physics only)
Scientific ideas change as new evidence arrives.
- Since 1998, observations of very distant have shown that distant galaxies are moving away faster and faster. The expansion is speeding up.
- Scientists think something called is causing this.
- Galaxies spin so fast that the matter we can see isn't enough to hold them together. Scientists think there is extra, invisible .
No one yet knows what dark matter or dark energy actually are. They are among the biggest unanswered questions in physics.