How is it proved that the Universe is expanding?
Astronomers measure the movement of objects relative to us using Doppler shift. When you hear a train coming, its whistle is heard at a different frequency compared to when it is receding, right? In the same way, light also has a Doppler shift, whereby its frequency is shifted depending on the motion of the emitting object.
Astronomers observed that light from distant objects in the universe is redshifted (shift in the frequency of light towards red color), which tells us that the objects are all receding away from us. This is true in whatever direction you look at: all the distant galaxies are going away from us. This can only be due to the fact that the Universe is expanding.
Further, by measuring the distance to the galaxies, one finds that the velocity of recession is proportional to the distance of the galaxy from us. This is called Hubble law after Edwin Hubble who was the first to discover it.
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- How fast is the Universe expanding?
- Can "tired light theory" explain the observed redshifts of galaxies?
- When measuring the expansion of the universe, do astronomers consider that they're seeing how galaxies moved long ago, not today?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist
This page has been accessed 24933 times since August 24, 2002.
Last modified: October 29, 2003 10:08:00 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)