by sc02492 » Fri Mar 10, 2017 12:21 pm
Wolf, the age of the universe is estimated to be around 13.8 billion years based upon the latest assessment of the Hubble "constant". It is tempting to interpret this as meaning that the observable universe should be 13.8 billion light years in radius, but that would not be correct, because it doesn't take into account the continued expansion (and acceleration) of space. So a photon emitted by a galaxy just outside of 13.8 light years distance (for instance) will still reach us, eventually, because space is continuing to expand and will eventually encompass the space where that photon was originally emitted. Just as important, that photon continues to travel towards us, as space continues to expand away from us, again meaning that we will eventually detect that photon (which will be more and more red shifted since the space that contains it continues to accelerate faster and faster away from us due to dark energy). This is a long winded way of saying that the observable universe has a much larger radius than 13.8 light years (it's estimated to be more like 46 billion light years in radius), due to the continued (and accelerating) expansion of space. Actually, based upon this logic, there is an entire universe beyond a radius of 46 billion light years, that we cannot see because the light emitted by objects at that distance is too red shifted to be seen in visible light.
Steve Cannistra
Wolf, the age of the universe is estimated to be around 13.8 billion years based upon the latest assessment of the Hubble "constant". It is tempting to interpret this as meaning that the observable universe should be 13.8 billion light years in radius, but that would not be correct, because it doesn't take into account the continued expansion (and acceleration) of space. So a photon emitted by a galaxy just outside of 13.8 light years distance (for instance) will still reach us, eventually, because space is continuing to expand and will eventually encompass the space where that photon was originally emitted. Just as important, that photon continues to travel towards us, as space continues to expand away from us, again meaning that we will eventually detect that photon (which will be more and more red shifted since the space that contains it continues to accelerate faster and faster away from us due to dark energy). This is a long winded way of saying that the observable universe has a much larger radius than 13.8 light years (it's estimated to be more like 46 billion light years in radius), due to the continued (and accelerating) expansion of space. Actually, based upon this logic, there is an entire universe beyond a radius of 46 billion light years, that we cannot see because the light emitted by objects at that distance is too red shifted to be seen in visible light.
Steve Cannistra