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
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