Cosmic Horizon Philosophy

Most recent answer: 12/25/2017

Hello Professor I have read that galaxies beyond the edge of the observable universe are receding from us with velocity greater than speed of light, and so we are not able to observe them, because no signal from them can arrive us. I know that speed greater than speed of light is possible in this case, as relative speed at same location only can't be greater than speed of light. But my question is if such galaxy exists, then what is the meaning of reality. I think reality means the thing which can be experienced by at least one of our sense organ. If no signal can arrive us from those galaxies, it means we can't perceive them by any means and hence they doesn't exists. Am I wrong?Thanks
- RAJESH KUMAR (age 36)
Norristown, PA, USA

Those are great questions that philosphers of physics think about, and we have no special answers.

There is at least one possible hole in the argument. If the universe continues its current pattern of accelerating expansion, nothing that's currently outside our cosmic horizon will return to a region where our descendants could experience it. That raises the issues you discuss. We are not at all sure that that will be the future pattern, however, since the origins of the acceleration ("dark energy") are not understood. So it is at least possible that there will be some future evidence about things now outside the horizon.

Mike W.

(published on 12/25/2017)

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