从理论上讲，如果你在一个距离地球1亿光年的行星上，回头看地球，我们会看到恐龙吗?

Marco Leonardi
Well yes, but actually no:
In theory? Yes, light that had hit the dinosaurs tens of millions of years ago is still wandering through space tens of millions of light years away.
But really? No; no alien civilization, no matter how advanced they are, could ever build a telescope big enough to catch light that is so far and sparse and focus it in such a way that you would see a dinosaur.
100 million light years is a very large distance, far more than the exoplanets that we have observed so far - aliens that far would be in a galaxy at the far edge of the Virgo cluster of galaxies.
The way photons can be focused responds to fundamental laws of physics, thus no amount of technological advancement could ever overcome it:
An observer at a distance of about 65 million light years (which is when the dinosaurs went extinct), would need a telescope of about 58 million km to be able to see Earth in a 1 pixel resolution. In order to get a glimpse of dinosaurs walking around though, the telescope lens would have to be of a diameter of over 4 light years.
You can already see the problem: such a big structure would firstly collapse in on itself, and even if it could somehow stand together, given the density and weight properties of glass, any glass construction over 28 light minutes will just turn into a black hole due to its gravitational pull.
More on the topic: “Could Aliens 65 Million Light Years Away from Earth See Dinosaurs Alive?” By The Infographic Show on YouTube.

是的，但实际上不是:
理论上？是的，数千万年前撞击恐龙的光仍然在数千万光年外的太空中游荡。
但实际上？不是。无论外星人有多么先进，都不可能能够建造一台大到足以捕捉如此遥远、如此稀疏的光线的望远镜，并从中观察到一只恐龙。
1亿光年是一个非常遥远的距离，远远超过了我们目前观察到的系外行星——那么远的外星人应该在室女座星系团的遥远边缘的一个星系中。
光子聚焦的方式遵循基本物理定律，因此任何技术进步都无法克服它: 一个距离6500万光年(恐龙灭绝的时候)的观察者，需要一台大约5800万公里的望远镜才能以1像素的分辨率看到地球。不过，要想看到恐龙在周围走动，望远镜的镜头直径必须超过4光年。
你已经可以看到问题所在:
这么大的结构首先会被自身的引力塌陷，即使它能立起来，考虑到玻璃的密度和重量属性,任何玻璃建筑超过28“光分钟”（光跑28分钟的距离）都会由于它的引力而变成一个黑洞。

Less Dumb Each Day
I am writing a sci-fi comedy cartoon that aims to be as accurate and well-researched as possible. So I actually have recently run some calculations for the L1 Lagrange point and it works out to around 902 km diameter for the front glass element. That’s very very very big. So big in fact that we are close to the radius of Pluto and it’s closely related obxts, all around 1100~1500 km in radius. So you can imagine a roughly Pluto sized dwarf planet that could support such a large lens taking up a relatively huge fraction of its surface. But you can only be about 1.5 million km away from Earth in this case if you want high resolution. This would give you 1 mm of dinosaur = 1 pixel of dinosaur from that distance, which is quite spectacular resolution.

我正在写一部科幻喜剧卡通，旨在尽可能准确和充分研究的基础上（创作）。
我最近对拉格朗日L1点做了一些计算，计算出前玻璃组件的直径约为902公里。这是非常非常大的。事实上，它是如此之大，以至于它接近冥王星的半径——其半径都在1100~1500公里左右。所以你可以想象一颗冥王星大小的矮行星，并支持如此大的透镜占据它表面相当大的一部分。并且在这种情况下，如果你想要高分辨率，你必须离地球大约150万公里。
这将让你看到1毫米的恐龙，从距离上讲是1像素的恐龙，这是相当“壮观”的分辨率。

Paul Chitescu
You could build a mirror made up by “carefully aligned” patches that can be much lighter and offer the same resolution, even if not collecting the same amount of light.
However:
- How to keep all those mirrors in alignment over several light-years and in presence of gravitational fields?
- It would still require disassembling several giant planets or a small star for materials.
- No Kardashev 2+ civilisation is going to spend such a titanic effort just for an entertainment show with dinosaurs

你可以用“仔细排列”的贴片来制作一面镜子，即使不收集相同数量的光，它也可以更轻，并提供相同的分辨率。
然而，
在引力场存在的情况下，如何让所有这些镜子在几光年的距离内对齐?
它仍然需要分解几颗巨大的行星或一颗小恒星的物质才能得到同等质量的镜子。
卡尔达舍夫2+文明不会花这么大的精力去看恐龙的娱乐节目。

Surya Kameswara Rao Ravi
I think the light though still be travelling somewhere in the universe the quality or resolution is still doubtful provided 100 million light years away between the observer and the obxt there is no impedence like black holes, nebulae, other solar systems, quasars, etc.

我认为光虽然仍然在宇宙的某个地方传播，但即便观察者和光之间没有黑洞、星云、其他太阳系、类星体等的阻挠，观测到质量或分辨率仍然值得怀疑。

Brian Scheetz
I believe some authors have speculated that utilizing black hole gravitational lensing might bring the scale of the telescope required down to a level feasible for a space faring civilization. You still have that pesky “achieve FTL travel” obstacle to overcome, though.

我相信一些作者已经推测的那样，利用黑洞引力透镜可能会将望远镜的规模降低到太空旅行文明可行的水平。
但是你仍然需要克服“实现超光速旅行”的障碍。

Martin Vratny
Well, yes, but actually no.
While 4 light years is a bit of problematic sizewise, you can easily build telescopes larger than the Earth. The 58 million kilometer one could be built today. Given enough cash.
It doesn’t need to be a solid obxt. Just a swarm of satellites that share data. As long as the edges of the swarm are at a distance of 58M kilometers, you’ve got your telescope.
The more of them, the better of course.
Recently, they did something similar when photographing the black hole last year. Turned two telescopes on the opposite sides of the planet towards one spot and turned them into a single Earth-sized telescope.

是的，但实际上不是。
虽然4光年的尺寸很有挑战，但你可以很容易地建造比地球大的望远镜。这条5800万公里长的望远镜今天就能建成，只要钱给够。
它不需要是固体。只是一群共享数据的卫星。只要卫星群之间的距离为5800万公里，你就有了望远镜。当然，卫星越多越好。
最近，他们在去年拍摄黑洞时做了类似的事情。把两个位于地球两侧的望远镜对准一个点，然后把它们变成一个地球大小的望远镜。

You could always trick it. If we assume the alien species is spacefaring (at sub c), and colonised close-by solar systems, they could build arrays in each of them, point all of them at Earth, and gain the image of the surface and dinosaurs alike (all of them combined would act like a light-years sized telescope).
It would take decades to collect the data in a central location, and calculating which photon is which would be a bitch of immeasurable proportions… But no black holes in sight.

你总是可以欺骗它。如果我们假设外星物种正在太空飞行，并在附近的太阳系定居，它们可以在每个太阳系中建立阵列，将所有阵列指向地球，获得地球表面和比如恐龙的图像(所有这些加起来就像一个光年大小的望远镜)。
在一个中心位置收集数据需要几十年的时间，这需要计算出哪个光子是哪个，且视野中不能有黑洞，这是一项难以估计的挑战。
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Enoch GroßFluss
Meh, i’m sure if there’s more to the science that humans know, then it’s possible that “super advanced aliens” can just do better than us. There might even be some “super advanced alien” better way of creating telescopes with “time reading” ability.

我相信如果人类所了解的科学越多，那么“超级先进的外星人”可能比我们做得更好。
甚至可能有一些“超级先进的外星人”以更好的方式创造具有“时间读取”能力的望远镜。

Han Prince
Well, yes, in theory, assuming you could get around the the technical problems (big enough telescope, clouds in the atmosphere, dust in space, etc.) you could see the dinosaurs.
If you ever look up into the sky and look at sky and notice the constellation Orion, one of the stars your seeing is the red giant Betelgeuse. It’s 642 light years from Earth. You are seeing what it looked like more that six centuries ago (Well before Columbus sailed the Ocean Blue). At some point Betelgeuse, because it is a red giant, will go up in a supernova as a spectacular explosion that maybe 20 times brighter that the full moon and probably will be visible in the day time. In fact, it may have already have gone supernova (though probably not). If it had done so on the day Columbus set sail from Spain, centuries ago, we would still would not know, because the light from that explosion is still more than a century away from us.
Anytime we look into the sky at the stars, we are seeing the past. In fact, even when you look into a mirror, you are seeing yourself in the past, if only by a tiny, tiny fraction of a second.

是的，理论上，假设你能绕过技术问题(足够大的望远镜，大气中的云，太空中的灰尘，等等)，你就能看到恐龙。
如果你抬头仰望天空，注意猎户座，你看到的其中一颗恒星就是红巨星参宿四。它距离地球642光年。你现在看到的是六个多世纪前的样子(远在哥伦布航行蓝色海洋之前)。由于参宿四是一颗红巨星，在某一时刻，它将成为一颗壮观的超新星，其亮度可能是满月的20倍，可能在白天也能看到。事实上，它可能已经变成了超新星(尽管可能还没有)。如果它是在几个世纪前哥伦布从西班牙启航的那一天发生的，我们仍然不会知道，因为那次爆炸的光离我们仍然有一个多世纪的距离。
每当我们仰望星空，我们看到的都是过去。事实上，即使你对着镜子，你也看到了过去的自己，哪怕只有极短的一秒。

Ronnie Grondin
Theoretically yes….
But you might want to try something a little closer. For example the Andromeda Galaxy is 2.537 million light years from Earth. If you are really lucky you might find Earth from this distance and see a world yet conquered by humans. The furthest picture of Earth we have is this photo:
This was taken by voyager 1 at the edge of the solar system. When this photo was taken Earth in the photo was 8.76 hours in the past.

理论上是的……
但你可能想试试更近一点的。例如，仙女座星系距离地球253.7万光年。如果你真的幸运，你可能会在这个距离发现地球，看到一个人类征服的世界。我们所能看到的、最远的地球图片是这张照片:

这是旅行者1号在太阳系边缘拍摄的。这张照片拍摄时，是地球8.76小时前的过去。
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Emilio Trampuz
Yes, beings in a galaxy that is 65 million light years away from us are right now seeing the Earth as it was 65 million years ago. That’s how long light had to travel from Earth to that galaxy.
So, yes, in theory, they could be seeing dinosaurs on Earth, assuming that they have telescopes powerful enough to see such details on Earth. But it is doubtful that such powerful telescopes could ever be developed.
From a place 65 million light years away, even our enormous Sun looks like just a single point of light. Even the most powerful telescopes we have cannot see any stars as round balls. Even the nearest stars (just 4 light years away) look like pinpoints of light. Each star is just a single dot.
From such enormous distances that the Sun is just a dot, a planet like our Earth would be less than a dot, …. almost invisible. So, seeing details the size of dinosaurs is practically impossible.
So, to summarize, those far away aliens are seeing Earth the way it was 65 million years ago, but they simply cannot see any details.

是的，在一个距离我们6500万光年的星系里的生物现在看到的是6500万年前的地球。这是光从地球到那个星系需要的时间。
所以是的，假设他们拥有强大到足以看到地球细节的望远镜，理论上他们可以看到地球上的恐龙。
从6500万光年外的地方看，即使我们巨大的太阳看起来也只是一个光点。即使是我们拥有的最强大的望远镜也无法看到任何圆形的恒星。即使是最近的恒星(只有4光年远)看起来也像精确的光点。每颗星星只是一个小点。
从如此遥远的距离去看，太阳只是一个点，像地球这样的行星可能还不到一个点，....几乎看不见。所以，看到恐龙大小的细节几乎是不可能的。
所以，总结一下，那些遥远的外星人看到的地球是6500万年前的样子，但他们看不到任何细节。

Chris Harper
No. You’d need one hell of a good telescope to see dinosaurs at that distance. We’re talking one made with exotic materials and had a aperture over a light year wide. Such a thing would literally be crushed under it’s own weight.
A very good telescope could, at that distance, maybe make out that there’s a planet around the Sun. It wouldn’t be able to make out any detail on the planet. I mean this is the best image of Pluto that we could get with terrestrial telescopes.
And you’re talking 165 million light years away?
No. You couldn’t see dinosaurs.

不。你需要一台极好的望远镜才能在那么远的距离看到恐龙。我们说的是一种由奇异材料制成的、超过一光年宽的光圈。这样的东西会被自己的重量压碎。
一个好的望远镜，在那样的距离，也许能发现太阳周围有一颗行星。它无法分辨出行星上的任何细节。我的意思是这是我们用地面望远镜能拍到的最好的冥王星图像。

这是我们用哈勃拍到的最好的照片

你说的是一亿六千五百万光年外吗?
不，你看不到恐龙。