But only after 10 years. You couldn't see anything that wasn't visible from the viewpoint of the mirror beforehand, as from earth's point of view the mirror isn't there yet. And if you're there anyway… you can just look at Earth with the craft that's on the position of the mirror already.
this post was submitted on 28 Oct 2025
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That's why we need to find a natural mirror somewhere already out there, so we can see into our past. Something like a planet made of pure mercury, or an arrangement of blackholes doing gravitational lensing that bends our light back to us, or whatever. We'd also need instruments vastly superior than what we currently have in order to get any useful information out of seeing our own light bounced back to us from so far away
... But still! the idea that it's at least hypothetically possible to actually see our own past is very exciting!
I'm assuming the inverse square law would hinder us from seeing anything useful. But now I'm imagining scientists being ecstatic about discovering a foreign signal, only to realise its us from the past
That's highly unlikely basically because of the inverse square law. Even tightly focused beams dissipate quite effectively over light-hours, let alone light years. We'd be lucky to catch a single photon from our past selves over any significant distance.
For reference, look up how weak the signal is even just coming back from the moon when people try to hit the retroreflectors with lasers. Or how crazy weak the signals are when they reach Voyager.
… But still! the idea that it’s at least hypothetically possible to actually see our own past is very exciting!
We... we have tools for seeing our past. We have extensive records of imagery from as far back as we have orbital satellites. You can go on Google Earth right now and look at older maps.
I mean, I get why it would be cool to see a reflection from the past, but literally every reflection you see is from the past. At a certain distance from your reflective or distorting surface, you're going to need major image processing to make out a clear image of the planet, so again, at that point it's far easier to just look at recorded images or videos.
There is a much cooler idea though that you can exploit from this principle: you can use a star or other dense object in space to work like a light-lens, we could build this now but it would be a very expensive and long-term project, because we would need to send a series probes out past the distance that Voyager 1 has already traveled over 40 years. We would also need to know ahead of time what our target is so we place the probes in the right place, placing the sun between the probes and the target at just the right distance.
If you take the distorted light from around the edges of the Sun and reconstruct it, you can theoretically see details of continents and other surface features of Earth-sized planets in entire other solar systems, which would be fantastic.
it's far easier to just look at recorded images or videos.
You're missing the idea of why this is cool. Recorded images only go back a couple hundred years
Only after 20 years. Light will take 10y to make it from earth to the mirror, and 10y to travel back.
No, the light would be reflected as soon as the mirror is set up. If the mirror is set up 10 lightyears away it would take 10 years for you to see it and whatever it reflects. There already is light on the way to the position of the mirror before you set it up.
Oops, that's right!
it takes way more than 10 years to ship a mirror from Earth to some place 10 ly away from earth.
None of these sound like deal breakers to this great idea
Also it would take at least 10 years to put a mirror there.
NASA: We’ve been getting a lot of footage of you being cringy in high school.
oh god oh fuck there's indestructible physical evidence of my Homestuck phase
Meh, amateurs. Being cringy as a kid at times is pretty much inevitable. That's when you learn your ways.
You can watch me being cringy as an adult for decades.
You can already do this with the light bent around black holes, it's just a bit hard to make out the image... make sure you wipe down your black hole with a damp cloth, you don't want a smudgey black hole
"Aw man... that's the third goddamned cloth I've dropped into this goddamned event horizon this week... and it's barely just Tuesday."
Instructions nuclear, toaster stuck in black hole
Redd Foxx was ahead of his time.
and if you look through the butt end of the telescope, you can see in the future
Isn't the butt end, the end you normally look through? I'd think the end facing the stars would be the front end.
It'd actually be cool as fuck if we could make some kind of Paycheck-style time machine that lets you see into the past by simply looking at light reflected off other celestial objects.
It could theoretically work looking backwards, but not forwards as it was used in the film. Of course, it'd have to have insane resolution for it to be like a video of what happened on the planet and not just a dot of light.
time machine that lets you see into the past by simply looking at light
You mean, this ?
lol
Real time, tho. That way we can see photographs from before cameras, too. Watch what dinosaurs were doing n stuff.
Unfortunately light wouldn't remain collimated over a 33 million light year distance which is what we would need to see dinosaurs
How about heat? Or some other radiation? 🤔
Alternatively, and slightly cheaper, put a satellite into orbit and just record everything on the ground it looks at, hang onto recordings for 10 years.
But that's boring, doing it with light is way better.
Also the governments already do that and don't want to share.
But that’s boring, doing it with light is way better.
I get that it seems cooler, but you would be looking at recordings with gathered light either way.
I can get nostalgia looking at my previous address on Maps because it shows my old Jetta (my first car) in the driveway :D
Google maps is one of the only applications that has literally made cry. The other is excel for entirely different reasons.
Google Earth/Maps in VR is pretty wild for visiting memory places.
As if we're not already doing that
Exactly, you can go on Google Earth right now and view the past.
You may need to squint a little.
If you did this quickly with a warp drive or whatever, you would still need at least ten years to see the results, so you could only see as far back as when you put the mirror up at the most.
No, you can see 20 years into the past, but only in 10 years. If you managed to will it into existence now, the light that left us 10 years ago would arrive at the mirror now and start heading back. That light would hit earth 10 years from now, so in 2035 we'd be able to see 2015
Big brother called, you weren’t supposed to leak this hack.
If only they did work into the future then they could have stopped you from spilling the beans.
Yeah, but it'd take us strictly longer than N years to place a mirror N light years away form Earth, so kinda useless.
We just need to point our telescopes towards the phantom zone where Zod and his buddies can reflect the light back.
Or youd see 20 years into the future... Let that one bake your noodle for a spell...
No you always see into the past.
Light cannot travel back in time. The reflection you’d see in the mirror is the light that left the Earth 20 years ago.
The mirror always looks back... (insert annoying spooky laugh)
But, just to be less of a Halloween spookster. The mirror is placed in a rather exotic location in space, and between the mirror and the Earth is... wait for it... youre going to hate this lol... a naturally occurring closed timelike curve! See, I told you youd hate it lol.
No that's not how light works. It's not 20 years either direction otherwise you could use your bathroom mirror to see into the future