- The biggest questions in the Universe<\/strong><\/em><\/a><\/li>\n
- Which came first: stars or galaxies?<\/strong><\/em><\/a><\/li>\n
- How did the early Universe expand faster than light?<\/strong><\/em><\/a><\/li>\n<\/ul>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>The Universe has continued expanding since the Big Bang. Credit: BSIP SA \/ Alamy Stock Photo<\/span><\/figcaption><\/div>\n The Universe is expanding in the aftermath of the Big Bang explosion 13.7 billion years ago.<\/span><\/p>\n
During the time that light from an astronomical object has been travelling across space to the Earth, the Universe has grown in size.<\/span><\/p>\n
The effect of this is to stretch the \u2018wavelength\u2019 of the light, much as a wave drawn on the fabric of a balloon would be stretched if the balloon were inflated.<\/span><\/p>\n
The wavelength of red light is about twice that of blue light, so the stretching of visible light shifts it towards the red end of the spectrum: thus the term \u2018redshift\u2019.<\/span><\/p>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>The further away a galaxy is, the more its light is shifted to longer wavelengths \u2013 an effect known as redshift<\/span><\/figcaption><\/div>\n What is the redshift z value?<\/strong><\/h2>\n
The letter \u2018z\u2019 is used by astronomers to denote the \u2018redshift\u2019 of a celestial object such as a galaxy<\/a>.<\/span><\/p>\n
The redshift is defined as the fractional change in the wavelength of the light: that is, the observed wavelength minus the emitted wavelength divided by the emitted wavelength.<\/span><\/p>\n
An object with a redshift of z emitted its light when the Universe was 1 \/ (1 + z) of its present size.<\/span><\/p>\n
With this definition, objects on our doorstep have a redshift of zero.<\/span><\/p>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>A snapshot of the Cosmic Microwave Background \u2013 heat left over from the Big Bang \u2013 when the Universe was just 380,000 years old, as seen by the Planck Telescope. Credit: ESA and the Planck Collaboration<\/span><\/figcaption><\/div>\n Conversely, a quasar with a redshift of 6 existed when the Universe was 1\/7th its current size and the cosmic microwave background<\/a> radiation \u2013 the \u2018afterglow\u2019 of the Big Bang fireball \u2013 with a redshift of about 1,000, comes from an epoch when the Universe was about 1\/1,000th its present size.<\/span><\/p>\n
The redshift of an object is not related to its distance in a simple way. This is because the Universe has not expanded at a constant rate.<\/span><\/p>\n
It expanded faster than average in the beginning and is expanding faster than average again today.<\/span><\/p>\n
\n - Which came first: stars or galaxies?<\/strong><\/em><\/a><\/li>\n
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