3 ms·
You need natural mirrors, because as others have pointed out, they have to already be there, you can't get ahead of the light to put them there. It has been su
by jerf 7y ago
You need natural mirrors, because as others have pointed out, they have to already be there, you can't get ahead of the light to put them there.
It has been suggested that black holes could provide this mirror, but it requires resolving not just something the size of Earth, but something much smaller, at a distance of 30 million light years +. Unfortunately you actually start hitting up against the limits of spacetime's resolution itself fairly quickly. But at least in principle, it is possible that some lucky photon has bounced off a dinosaur, and has traveled all the way out there, and all the way back to Earth, just now, that if you knew where to look in the sky, perhaps such a photon might even enter your eye now. Or perhaps there is some human out there who really has "seen" the dinosaurs. But you'd never really know.
- klank 7y agoWhat are these "limits of spacetime's resolution" you speak of? Beyond speculation, I'm not aware of anything showing spacetime to be discrete.
- fmihaila 7y ago> What are these "limits of spacetime's resolution" you speak of? > Beyond speculation, I'm not aware of anything showing spacetime to be discrete. It is a prediction of loop quantum gravity [1]: In 1988, Carlo Rovelli, Lee Smolin, and Abhay Ashtekar introduced a theory of quantum gravity called loop quantum gravity. In 1995, Rovelli and Smolin obtained a basis of states of quantum gravity, labelled by Penrose's spin networks, and using this basis they were able to show that the theory predicts that area and volume are quantized. This result indicates the existence of a discrete structure of space at very small scale. [1] https://en.wikipedia.org/wiki/Carlo_Rovelli#Loop_quantum_gravity https://en.wikipedia.org/wiki/Carlo_Rovelli#Loop_quantum_gra...
- jerf 7y agoIt's a prediction of other things, too. Even just sheer every-day quantum mechanics sets a limit, too; eventually you're asking to nail down a photon's origin with so much precision that you lose the frequency or something, things you don't normally think about even in the most extreme astronomy today, but become relevant when discussing bouncing photons around a black hole 30 million light years away.
- klank 7y agoModern QM formalization doesn't predict a discrete spacetime. Or, if it does, nobody has been able to demonstrate this, to my knowledge.
- DataGata 7y agoEventually you will get so far away from something that you cannot resolve it even at the plank distance.
- klank 7y agoHow does that necessitate a discrete spacetime?