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末世猜想:可能導致人類滅亡的幾大威脅

The greatest long-term threats facing humanity
末世猜想:可能導致人類滅亡的幾大威脅

Can we actually say anything about the far future? If we can’t predict when it will rain next month, forecasting billions of years hence might seem impossible.

遙遠的未來會是什么樣子,我們真能說得準嗎?連下個月什么時候下雨都不知道,預想幾十億年以后的事情似乎只能是天方夜譚。

However, not everything is as chaotic as the weather: even predictions very far ahead are sometimes possible, especially in astrophysics and cosmology. We can be confident that there will be a total solar eclipse in the UK on 23 September 2090 because the Moon, Sun and Earth move in stable, predictable orbits with very minor disturbances, and the laws of gravity are now well-tested. Similarly, we can use known astrophysics to predict what will likely happen across the Universe as it expands.

不過,并非所有事情都像天氣那樣混沌難測,預測遙遠的未來也是有可能的,特別是在天體物理學和宇宙學方面。我們能夠肯定,2090年9月23日這一天英國一定會出現日全食,因為月亮、太陽以及地球都是沿著可預知的軌道在穩定運行,受到的干擾微乎其微,而且萬有引力定律也已經得到全面證實。同樣地,我們也可以利用已知的天體物理學知識預測出在宇宙膨脹的過程中可能會發生哪些事情。

This approach can be described as “physical eschatology” – a term coined by the astronomer Martin Rees for using astrophysics to model where the Universe is going. Rees took a cue from theology, in which “eschatology” is the study of ultimate things such as the end of the world. And the classic paper on the topic is Freeman Dyson’s 1979 paper on life in open universes, which outlined likely or possible existential catastrophes that could threaten life far into the future, from the death of the Sun to the detachment of stars from galaxies.

這種預測方法被稱之為“物理末世論”,由天文學家馬丁‧里斯(Martin Rees)提出,利用天體物理學建構的模型,預測宇宙的發展。末世論在基督教神學領域研究的是世界末日等終極問題,里斯正是借鑒于此。相關的經典之作是戴森(Freeman Dyson)在1979年發表的一篇文章,討論開放宇宙中的生命前景。論文認為太陽死亡,以及恒星逃離銀河系等可能存在的災難都會對遙遠未來的地球生命造成威脅。

So, what are the biggest challenges humanity will face if we survive into the far future? We cannot say how (or if) they will be overcome (I will make some guesses) but we can be confident these threats to our existence are coming.

那么,如果人類能夠延續到如此遙遠的未來,會面臨什么樣的最嚴峻的挑戰?我們并不知道該如何克服這些挑戰,或能否克服這些挑戰,此處我只能做一些猜測。但可以肯定的是,這些事關人類文明存亡的威脅正在向我們迎面而來。

Problem 1: Survive better than other mammals

問題1:人類能否超越哺乳動物宿命

The typical lifespan of a mammalian species is about a million years or so. From nuclear war to bioengineered pandemics, humanity clearly has other risks it needs to reduce urgently: right now the natural extinction rate is far smaller than risk we pose to ourselves.

一個典型哺乳動物物種的存在時間大約為100萬年。對人類而言,除了從核戰爭到生物工程可能引發的傳染病,還有其他可能毀滅人類的危險迫切需要面對和解決。今天,人類自作孽造成的滅絕風險已遠遠高于發生自然滅絕事件的概率。

Were we to fix our current existential risk and sustainability problems we would still have to deal with some other challenges to stay around.

要想解決現有的人類生存風險以及可持續問題,我們還得應對許多其他挑戰。

For starters, in a few tens of thousands of years we will have to cope with the end of the current interglacial period: we are living during a brief interruption of a long ice age. Our ancestors have survived ice ages, so it is likely not a big deal – except that they were nomadic hunter-gatherers rather than a global civilisation.

人類在未來幾萬年內,首先面臨的是本次間冰期(兩個冰河期之間的時期)的結束。目前人類正處于一個漫長冰川時代中的一個短暫溫暖的間冰期之中,間冰期結束,地球將會變得非常寒冷。不過我們的祖先活過了冰川時代,再過寒冷生活可能問題不大,只不過我們的祖先是游牧人,靠狩獵采集維生,還沒有一個全球性的文明。

We may also face dramatic climate variations between different geological eras. In the past the Earth has been not just colder, but also warmer. During the Eocene, temperatures were 10C warmer, with palms and alligators in the Arctic and equatorial regions too hot for unprotected humans to survive in. Even further in the past there has been “snowball Earth” episodes where almost all of the Earth was covered with ice.

人類還可能經歷不同地質時期之間的氣候大變遷。在遠古時代,地球曾經非常寒冷,但也曾經非常暖和。在5600萬年前到3400萬年前的始新世地質年代,地球的氣溫要比現在高10攝氏度,北極也有棕櫚樹和鱷魚,而赤道地區則太過炎熱,人類如生活在這樣的赤道,不采取保護措施根本無法生存。再往前還有過“冰雪地球”時期,當時整個地球基本都被冰雪所覆蓋。

Then there is the risk of supervolcanism, meteor impacts, gamma ray bursts, or emergent ecological disruptions, which we know have led to natural mass extinctions about once every 100 million years.

此外人類還可能遭遇超級大火山噴發、小行星撞地球、來自宇宙的伽馬射線暴,或緊急生態大災難等能毀滅人類文明的種種危險。我們人類已知,上述大災難曾導致地球約每1億年就會出現一次物種大滅絕事件。

Ultimately, Homo Sapiens may not endure as a species because we could evolve into something else. We are constantly mutating and subject to natural selection (even today with good healthcare, road accidents are slowly selecting away people likely to kill themselves in traffic while young), and modern biotechnology allows us to modify our genes deliberately. Not to mention technologies that allow us to merge with the artificial. Over millions of years it is unlikely that we will stay the same – unless we make a deliberate decision to preserve our genetics and can make that decision stick over geological timescale.

最終可能不再有智人這個物種存在,人類可能會進化成一個新的物種。人類一直在演化變異中,并受到物競天擇的自然篩選,即或如今醫療條件良好,但交通事故也會讓人英年而逝,猶如是一種自然淘汰。現代生物科技也讓我們能夠改良自身基因,甚至還有能將人與人工合為一體的科技。相信再過幾百萬年,未來的人類將會與我們是面目全非,除非我們有意決定維護我們的現存基因,不讓其發生任何的改變,并在未來漫長的地質年代中一直堅守到底。

If “we” are around in a billion years from now, we would have arbitrarily sustainable civilisations able to handle disasters on a planetary scale, plan ahead for geologic time, and likely be as different from us as we are from the trilobites. The irony is that to survive longer than our fellow mammalian species, we have to become something very different from what we are.

如果“人類”(姑且仍稱之為人類)10億年后還存在,將一定會擁有可傳之久遠的文明,能夠應對行星級別的大災難,能夠規劃以地質年代為單位的人類前景,那時的人類跟現在的人類相比,差異之大就跟我們當今人類和二億五千萬前已滅絕的三葉蟲的區別差不多。人類要想比其他哺乳類動物活得更長久,就得大變身成為其他物種,說來也是諷刺。

Problem 2: Survive the end of the biosphere lifespan

問題2:能否存活到地球生物圈終結之后

In about a billion years (give or take a few hundred million years) the increased brightness of the Sun will doom the Earth’s biosphere.

再過10億年(或者前后差個幾億年),太陽光亮度的增強會給地球上的生命帶來滅頂之災。

The problem is that the heat of the Sun leads to increased weathering of rock, which in turn leads to chemical reactions that removes significant amounts of carbon dioxide from the air as part of the carbon cycle, eventually starving plant-life. In addition, the planet eventually overheats as a runaway greenhouse, with more and more water vapour (a potent greenhouse gas) evaporating from the oceans, making it even hotter.

太陽熱量的增加會加劇巖石的風化,從而引發一系列化學反應,消除空氣在碳循環過程中的大量二氧化碳,最終摧毀以二氧化碳進行光合作用的植物。此外,地球會熱得像一個失控的溫室,從海洋中蒸發出越來越多的水蒸汽,從而使得地球更加炎熱。

One approach is to try to protect the biosphere with megascale engineering for as long as possible. We may perform geoengineering by adding reflective aerosols to the stratosphere, build a solar shade between the Earth and Sun, or even move the planet outwards.

其中一個辦法是建造超大規模的工程,盡可能長時期保護地球生物圈。那時的人類還可以實施地球工程,在平流層添加能夠反射太陽光的懸浮顆粒,或是在地球與太陽之間建造一個太陽遮板,甚至可以把地球往遠離太陽的方向移一移。

Another solution is to move life into space, if we have not already done so. Self-sustaining space habitats appear possible, and there is material out there for many billion times the Earth’s surface area. Even if these structures appear hard to build, we should remember that we literally have a billion years to become more skilled, richer, and to work on them.

另一個解決之道是將地球生命轉移到太空,當然要是那時人類還沒開始太空移民的話。宇宙看來存在適宜生命居住的行星,而且太空中的物質要比地球表面積大好幾十億倍。就算人類移民太空的工程是非常的艱巨,但請別忘了,我們人類還有10億年的時間來提高技術,增加財富,進行建造。

By this point humanity has to be an actor on the scale of the Solar System if it is to survive.

到了這個關頭,人類文明要想延續下去,就必須到太陽系中去建立新的家園。

Problem 3: Survive the end of the Sun’s main sequence lifetime

問題3:人類能活到太陽功能減弱之后嗎

In around 5 billion years, the Sun’s brightness will start to increase more rapidly because accumulated helium in the core will heat it up, turning it into an enormous red giant. The surface temperature goes down but the total light output is far larger due to the huge surface area. This likely spells the end for the Earth, since it is likely to be swallowed by the Sun as it expands. If it isn’t, it will be fried to an airless rock. “Soon” after (a billion years or so) the Sun will expel much of its atmosphere as a nebula and becomes a tiny white dwarf.

再過大約50億年,太陽核心的氫聚變反應加快,氦元素逐漸增大,太陽的明亮程度會快速增長。這時的太陽結束其主序星階段,膨脹成一顆碩大的紅巨星。雖然這時太陽的表面溫度會降低,但由于表面積巨大,所輻射的光將遠遠超過現在的太陽。這時地球的末日也就到,很可能會被不斷變大的太陽所吞噬。就算沒有被太陽吃掉,也會被空前強烈的太陽光煎烤成一塊連一絲風一滴水都沒有的大石頭。之后太陽“很快”(這是以宇宙的時間而言,但大約也要10億年)將其絕大部分物質向外拋出,形成星云,這時的太陽會變成一顆小型的白矮星。

To survive this, any intelligent life living in the Solar System will need to move to other solar systems. One can of course adapt but there is not much light and energy from a white dwarf.

太陽系的智慧生命要想躲過此劫,就必須移民到其他星系。那時已達超級智慧的人類當然也可以嘗試去適應此時的環境,但變成白矮星的太陽已沒有多少的光和能量可以發出,人類不得不離開太陽系。

Reaching other solar systems will either require very fast spacecraft, or will take a long time.

要到達其他星系建立新家園,需要速度極大的航天器,否則就要花上非常漫長的時間。

To people already living on self-sufficient space habitats, setting them in motion towards new destinations might be fairly natural. They would need energy sources that could last for a long time (not to mention to give them a decent speed) and enough material to maintain the habitat for the multi-millennia transit.

對于已經生活在自給自足的太陽系太空生命基地上的未來人類,當太陽死亡,移民外星系,尋找或建立新的生命家園也是很自然的事情。但這需要源源不斷維持很長時間的能量供給,而且前往太陽系外的星系,飛行速度也不能太慢。此外還要有足夠的物質來維持這場跨越千年的遷徙。

The most likely way to get to the stars might, however, be tiny nanorobot spacecraft. Instead of using vast energy to push giant starships to a modest velocity, it might be better used to send tiny craft fast using a reflective sail and a powerful laser. They are small and redundant: if one does not make it, send a thousand. They could also carry the genetic elements to create life – even human beings. Once they arrive, they land on a suitable asteroid, unfold solar collectors, mine material and build more robots, solar collectors and factories. Eventually they can build habitats and nurture people to live in them.

飛往太陽之外的星系最有可能的方式,是使用小型的納米機器人太空器。大型星際飛船需要巨大能量才能達到一定速度,使用小型太空器可以利用反光帆板和強勁射線推動快速行進,效果會更好。納米機器人太空器不僅體積小,而且可大量使用。如果發射一個失敗,那就發射一千個。納米太空器還可以搭載著遺傳基因以創造生命,甚至搭載人類。到達其他星系后,這些小型太空器可以在適合的小行星上降落,打開太陽能收集器,開采物質,并制造更多的機器人、太陽能收集器以及工廠。最終,建成一個個太空棲息地,讓人類能夠在這些機器人建造的生命基地上繁衍人類文明。<-->紐約時報中英文網 http://www.zvkdrb.live<-->

It might well be that no biological human will ever physically leave the Solar System. At this point we might question whether it is actually our humanity or a new species that is spreading. But if our descendants survive the red giant Sun they will now be living among the stars of the galaxy.

稱之為人類的這一地球物種可能永遠也無法離開太陽系。此刻,我們可以提出這樣的問題,向太陽系外的星系發展的智慧生命到底是我們人類自己,還是一個新的生命物種。但無論如何,人類的后代如果真的能熬過太陽變成紅巨星這個災難,活了下來,那一定應該已生活在銀河系的其他的恒星之中。

Problem 4: Survive the end of stars

問題4:能存活到恒星消亡之后嗎

Star formation in the Universe has already peaked and in the next few tens of billions of years we will reach “peak star”. As the bright and short-lived stars burn out, we will be left with a staid but long-lived population of red dwarf stars. They can shine for trillions of years. But star formation will decline, and in 10-100 trillion years even the red dwarfs will sputter and go out. To survive, life will need energy sources other than starlight.

宇宙的恒星形成的巔峰時期已經來臨,在未來的幾百億年里,我們將迎來最高“恒星巔峰”期。那時明亮且壽命較短的恒星將會燃燒殆盡,剩下的都是穩定且壽命較長的紅矮星,發光時間可達數萬億年。但是恒星形成的數量將會下降,再過幾千幾萬億年,紅矮星也將坍塌消散。生命要想存續,不能依靠恒星的光熱,而是需要其他能量來源。

There are actually many possibilities: fusion using hydrogen from brown dwarfs and gas planets, dumping matter into black hole accretion disks and gathering the released energy, or even tapping black hole rotation directly using so-called super-radiant scattering (known as “black hole bombs”). In any case it will require engineering on a vast scale. What about normal nuclear power? Fission power will end when there are no new radioisotopes produced by merging neutron stars and supernovas, which by now are long in the past. Geothermal energy also runs out when the isotopes inside planets decay away and they cool down.

可能性其實很多,可以使用褐矮星以及氣態行星上的氫制造核聚變產生能量,或是將物質投入黑洞的吸積盤中,收集釋放出的能量。甚至利用一種被稱為超輻射的東西(也就是所謂"黑洞炸彈")按一定角度拋入黑洞強大的旋轉盤,然后帶著新獲取的能量逃逸出來。不論哪種方法,都是巨大無比的工程。那么使用普通的核能可以嗎?如果沒有超新星爆炸合并旁邊的中子星而產生可裂變同位素,也就不會再有核裂變的能量。現在超新星爆炸已是非常久遠的事了。當行星內部的同位素逐漸衰變冷卻后,行星的地熱能也會消耗一空。

“Life” may also adapt to low temperatures and exotic environments. Artificial intelligence and silicon-based organisms would probably thrive in the near absolute zero temperature environment. It might well be that as the stars go out, carbon-based life and intelligence retreats into comfortable virtual worlds far bigger and more complex than the external Universe ever was.

“生命”或許也可以適應低溫和極特異的環境。人工智能及硅基生命或許也能在近乎絕對零度的環境中生存。在恒星陸續死亡后,也有可能是,碳基生命及其智慧體會退居到舒適的虛擬世界中,而這個虛擬世界比外部實體的宇宙還要廣闊和復雜。

If humanity survives the end of the stars, it will be the largest energy source in the Universe.

如果人類能夠活到恒星消亡之后,人類就會成為宇宙中最大的能量源。

Problem 5: Survive the end of galaxies

問題5:能活到銀河系消亡之后嗎?

Random stellar motions eventually cause galaxies to dissolve: from time to time stars pass by each other and change velocities randomly. Sometimes this gives a star an escape velocity from the galaxy and it disappears out into the great emptiness, leaving the rest of the galaxy slightly more condensed. Eventually – in about 100 million trillion years – all of the galaxy scatters or falls into the central black hole. Planets around the stars will also be flung away in the close encounters.

沒有規律的恒星運動最終會導致銀河系的解體。恒星彼此間不時擦肩而過,速度會隨機發生改變。有時,恒星因此獲得的速度能令它逃離銀河系,消失在無盡的虛無之中,而余下的銀河系則聚合得更加緊密。最終,在大約一萬億億年之后,整個銀河系的星體或者會四散于宇宙,或者全部掉入銀河系核心的黑洞之中。圍繞恒星運轉的行星也會在這一巨變中被拋離運行軌道。

To survive this, intelligent beings need to steer stars to put them into orbits that are long-term stable.

智慧生命要想逃過此大災難,就要將恒星引到長期穩定的軌道上來。

This looks physically possible! At least in the present era, one could nudge stars by placing reflectors so their radiation acts as very weak rocket engines, getting them to pass by each other in a controlled fashion. This is similar to how we humans used gravity assists to redirect and accelerate the Voyager probes, but now on a vast scale. As the stars change orbits they could be used to further nudge each other in the largest billiard game ever conceived.

從物理學的角度來說這是有可能的!就目前而言,至少可以用電磁波發射器微調恒星的運行。發射器發出的輻射就像小馬力的火箭引擎一樣能產生動力,以控制恒星相遇時的速度。這就好比人類利用其他天體的引力為兩枚外太陽系太空探測器旅行者號調整運行方向以及提升速度一樣,只不過要干擾恒星運行的電磁波發射器要巨大得多。這就像是一局最大型的臺球游戲,恒星在改變軌道時也可以進一步相互推動。

It would take big structures around every star and massive planning ahead, but the total amount of matter needed is about a big asteroid per solar system and the physics is relatively straightforward. The issue is more about coordinating projects on literally billion year timescales. Which by this time might be everyday planning for a humanity that has already handled the past problems.

這需要在每一個恒星周圍建造巨型工程,事前要進行巨大的規劃,而工程所需要的物質總量也很大,相當于每個恒星系大約就要一顆大型的小行星。而建造的物理原理則相對清晰明了。關鍵是要在十億年的時間跨度規劃協調這些工程項目。不過到那個時候,人類已經克服過種種難關,這樣的太空工程對他們來說可能不過是稀松平常事。

Problem 6: Survive the end of matter

問題6:存活到宇宙物質消散之后

Our kind of matter is built out of atoms composed of protons, neutrons and electrons. Protons and electrons are normally said to be perfectly stable (the neutrons are stabilised by the protons; on their own they decay with a half-life of a few minutes).

我們所謂的物質全部是由質子、中子和電子這些粒子所組成的原子構成的。質子和電子一般來說非常穩定。中子靠質子來穩定,其自身的半衰期只有幾分鐘。

However, many physical theories predict that protons are not truly stable and will decay over enormously long timespans. Proton decay has never been observed so far despite some heroic research efforts. But this merely tells us that it takes trillions of years, if it happens.

但許多物理學理論都認為,質子并非真的穩定,放到漫長的時間維度上看最終也將發生衰變。雖然科學界有過一些艱苦卓絕的研究,但目前還沒有觀察到質子的衰變。不過這只能說明如果質子真的會衰變,可能需要幾萬億年的時間。

This decay will spell the end of matter as we know it. Stars and planets will slowly turn into radiation plus free electrons and positrons, unable to form habitable systems. The last cold black dwarf stars would gradually turn into helium and hydrogen crystals that quietly evaporate in stillness. The only thing left would be radiation and black holes in an otherwise empty Universe.

質子的衰變將會終結我們所認知的物質世界。宇宙中的恒星與行星物質都會慢慢解體變成電磁波及自由電子和正電子,不能再形成能供生命棲息的天體。宇宙中最后一批寒冷的黑矮星(恒星殘骸)會逐漸成為靜止不動的氦晶體及氫晶體,直至灰飛煙滅。這時空曠的宇宙中只有一些基本粒子和黑洞。

Can we get around it? As the great computer in Isaac Asimov’s masterful short story “The Last Question” said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

人類能夠幸免于難嗎?答案可以參考阿西莫夫(Isaac Asimov)優秀的短篇小說《最后的問題》(The Last Question)。小說中一臺大型計算機的回答是:“數據不足,無法作答。”

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