but if , instead of retreating beyond the event horizon , the galaxy were to jump backward in time , then this would be , in every practical and functional sense , physically indistinguishablewhile we can still see the incidental light that was emitted before the galaxy had fallen away forever , this old , dead light reveals nothing ; there is indeed no measurement or method of detection that could correct one who believes that a causally isolated galaxy goes backward in time rather than beyond a horizon .