If the current energy density of the universe is indeed dominated by a cosmological constant , then high–redshift sources will remain visible to us only until they reach some finite age in their rest–frame .
The radiation emitted beyond that age will never reach us due to the acceleration of the cosmic expansion rate , and so we will never know what these sources look like as they become older .
As a source image freezes on a particular time frame along its evolution , its luminosity distance and redshift continue to increase exponentially with observation time .
The higher the current redshift of a source is , the younger it will appear as it fades out of sight .
For the popular set of cosmological parameters , I show that a source at a redshift z _ { 0 } \sim 5 –10 will only be visible up to an age of \sim 4 – 6 billion years .
Arguments relating the properties of high–redshift sources to present–day counterparts will remain indirect even if we continue to monitor these sources for an infinite amount of time .
These sources will not be visible to us when they reach the current age of the universe .