Tom Dempsey
Chadds Ford, Pennsylvania
It is a implausible query, and the reply highlights among the most counterintuitive facets of the idea of normal relativity. The quick reply isn’t any, however let’s delve deeper into a number of of the unusual issues that occur when objects strategy the velocity of sunshine.
To an outdoor observer, as an object falls towards the event horizon (the purpose of no return the place not even mild can escape the gravitational pull of a black hole), two results come into play. As mild leaves the excessive gravitational discipline surrounding the black hole and reaches the observer — who’s in a decrease gravitational discipline — it loses vitality. So, as a result of mild turns into extra crimson at decrease energies, the article appears to get redder and redder because it approaches the event horizon.
As well as, normal relativity predicts that when an observer in a low-gravity atmosphere observes an object in a high-gravity one, the observer will see time go extra slowly for the article. This slowing signifies that the sunshine emitted by the falling object might be unfold out over a for much longer time. In the event you scale back the speed at which mild is emitted, it can seem dimmer and dimmer. From the observer’s perspective, as the article approaches the event horizon, time will gradual to the purpose the place it can take longer than the lifetime of the universe for the article to emit particular person photons.
Thus, as an object falls towards the event horizon of a black hole, it can redden in look. It would additionally seem to emit mild extra slowly, and thus will turn out to be dimmer. The mix of those two results are that an exterior observer will see the article redden and fade out of sight, however they are going to by no means see it cross the event horizon.
Don Lincoln
Particle Physicist, Fermi Nationwide Accelerator Laboratory, Batavia, Illinois
