宇宙學常數問題，或稱真空災變（英語：Vacuum catastrophe From Wikipedia, the free encyclopedia） VS愛因斯坦一生最大的「錯」？？《中国科學報》

 From Wikipedia, the free encyclopedia

宇宙學常數問題，或稱真空災變（英語：Vacuum catastrophe），是當今物理學界中待解決的謎團之一，是指理論與觀察之間的一個巨大落差：根據量子場論的推算，真空中的零點能量應該非常龐大，但實際觀測到的真空能量值卻小得多，兩者相差極大。由於真空能量值是計算宇宙學常數的一個關鍵值，若對真空能量的估算出現偏差，整個宇宙模型也會隨之不同。^[1]

雖然該能量的理論值依據不同的理論條件（例如普朗克能量上限）而有所變化，但科學家在計算後仍然發現兩者之間的差距高達50到120個數量級。^[2][3] 物理學界認為這漾的差異是科學史上理論與實驗最嚴重的不符，^[2]甚至有人稱之為「物理學史上最差勁的理論預測」。^[4]

背景

"Vacuum catastrophe" redirects here. For other uses, see Vacuum catastrophe (disambiguation).

Beyond the Standard Model
Simulated Large Hadron Collider CMS particle detector data depicting a Higgs boson produced by colliding protons decaying into hadron jets and electrons
Standard Model
Evidence
Theories
Supersymmetry
Quantum gravity
Experiments
v t e

Unsolved problem in physics:

Why is the vacuum energy density much smaller than a zero-point energy suggested by quantum field theory?

(more unsolved problems in physics)

Beyond the Standard Model
Simulated Large Hadron Collider CMS particle detector data depicting a Higgs boson produced by colliding protons decaying into hadron jets and electrons
Standard Model
Evidence
Theories
Supersymmetry
Quantum gravity
Experiments
v t e

Unsolved problem in physics:

Why is the vacuum energy density much smaller than a zero-point energy suggested by quantum field theory?

(more unsolved problems in physics)

In cosmology, the cosmological constant problem or vacuum catastrophe is the substantial disagreement between the observed values of vacuum energy density (the small value of the cosmological constant) and the much larger theoretical value of zero-point energy suggested by quantum field theory.

Depending on the Planck energy cutoff and other factors, the quantum vacuum energy contribution to the effective cosmological constant is calculated to be between 50 and as many as 120 orders of magnitude greater than has actually been observed,^[1][2] a state of affairs described by physicists as "the largest discrepancy between theory and experiment in all of science"^[1] and "the worst theoretical prediction in the history of physics".^[3]

馮睎乾十三維度

愛因斯坦一生最大的「錯」

日前，《中国科學報》 有一則看來很聳動的新聞，標題為「出大事了，中国天文學家證明愛因斯坦可能錯了！」但未看內文我已經笑了，因為這句話根本沒有邏輯。何謂「證明⋯⋯可能錯了」？若已「證明」愛因斯坦錯了，就不必再說「可能」；若只是「可能」有錯，那你實際上並沒「證明」什麼。

愛因斯坦的相對論至今已提出超過一世紀，其間經過無數次的驗證，而每次國際天文學界有新發現，都只是反覆證明「愛因斯坦又中」而已。這次，中国天文學家到底挑出什麼錯誤呢？

4月9日，中国国家天文台發布一項研究，他們基於「暗能量光譜儀（Dark Energy Spectroscopic Instrument，簡稱DESI）」的相關資料，發現「暗能量（dark energy）」隨時間而變化，不是像愛因斯坦假設的「宇宙學常數（cosmological constant）」那樣一成不變。如果宇宙學常數不是常數，愛因斯坦不就是錯了？

事實上，根本不用勞煩中国天文學家出來「糾正」，愛因斯坦本人早於1931年就已放棄「宇宙學常數」這個假設，其後還跟友人（如George Gamow）說過，這是他一生「最大的錯誤（the biggest blunder）」。如果中国人現在真的能夠「證明」宇宙學常數是錯，其實還是證明愛因斯坦對了——證明他認錯是對的。

愛因斯坦第一次把宇宙學常數寫進他的宇宙模型，是1917年。當時他發現根據廣義相對論計算，宇宙應該在縮小，像被重力拉着往回跑。然而那個年頭，大家都深信宇宙是靜止的，就連愛因斯坦這位勇於顛覆既有觀念的智者也未能免俗，不想打亂宇宙的平靜。所以他把心一橫，往自己的方程式裏塞了一個新東西，叫「宇宙學常數」，代號Λ（唸成 Lambda），彷彿拿膠帶黏住理論的破口，然後跟全宇宙說：「不要動，你給我安靜地躺平下去。」

這個Λ，簡單來說，可以理解為遍佈宇宙真空的固定能量密度。在愛因斯坦最初的構想中，宇宙學常數的作用是抵消重力影響，確保宇宙處於既不膨脹也不收縮的穩定狀態。但到了1929年，哈勃（Edwin Hubble）發現宇宙其實正在膨脹，馬上顛覆了全世界的認知。事實勝於雄辯，愛因斯坦這才發現，自己用來給宇宙「維穩」的常數是多餘的。1931年，愛因斯坦修訂了他的宇宙模型，從善如流，將那個可疑的宇宙學常數丟進垃圾桶。

也許宇宙（或上帝）真的很喜歡跟人類開玩笑，當全世界都以為愛因斯坦也犯錯時，宇宙學常數卻在大半個世紀後離奇「復活」了——不過這次它並不是拿來令宇宙靜止，而是用來為「暗能量」代言。時間快轉到1998年。天文學家本來以為宇宙膨脹速度會慢下來，但他們觀測一些遙遠的超新星時，卻發現它們正在加速飛走，也就是說，宇宙正在加速膨脹！

是什麼驅動宇宙加速呢？科學家於是提出「暗能量」這個概念作解釋。通過計算，科學界普遍認為暗能量佔當今宇宙所有能量物質總和的70%左右。換言之，我們的宇宙有七成是由暗能量組成，而這七成到底是什麼，至今還沒有人（或AI）說得清。這麼奧妙的東西，應該怎樣寫進宇宙的方程式呢？這時，大家便從垃圾堆中翻出那Λ常數，小心翼翼重新供奉——它也許不是愛因斯坦的錯誤，而是被誤會了大半世紀的「神預言」。

這個宇宙故事，越說越玄妙。有人用量子場論算一下Λ的值，卻發現這個理論值跟實際觀察到的數值，居然相差10^120倍（即1字後有120個零）。什麼意思呢？不妨打個譬喻：科學家根據理論算出來的宇宙學常數是超級大的，就像十個宇宙加起來那麼大，但實際上觀測到的數值，卻只有一粒沙那麼小！你期待的是幾個宇宙，結果上帝只給你一粒沙，彷彿在調侃人類的自以為是。

看到這裏，你應該明白宇宙學常數這回事，本來就有很多糾纏不清的問題，跟現實落差很大，何況愛因斯坦也早已認錯，把這個常數棄如敝屣，而1998年後「被復活」的宇宙學常數2.0，意義和功能又偏離愛因斯坦原意很遠——愛因斯坦的時代，根本不知道有暗能量——在這樣的歷史背景下，你說中国科學家「證明」愛因斯坦「可能錯了」，分明是誤導讀者。

當然，中国天文學家團隊也是有貢獻的，但我想補充一點：他們賴以研究的資料來自DESI，而DESI 是由美國能源部資助、柏克萊實驗室 （Lawrence Berkeley National Laboratory）主導的大型國際合作計畫。中国團隊的確有份參與，但那個探測暗能量影響的強大儀器，是安裝在美國亞利桑那州的Mayall望遠鏡上。即使真的「證明」愛因斯坦錯了，中国團隊還是要跟美國say thank you。

相關文章：

中国熱賣「愛因斯坦的腦子」

https://www.patreon.com/posts/95911213

Google量子晶片「垂柳」，打開了平行宇宙？

https://www.patreon.com/posts/117764265

所有心情：

1,139你和其他1,139人

Scientists Map Miles of Wiring in a Speck of Mouse Brain 在繪製小鼠一立方毫米大腦圖時，科學家收集了 1.6PB 的數據——相當於 22 年不間斷的高清影片

 

科學家繪製出小鼠大腦中數英里長的神經連結圖

在繪製小鼠一立方毫米大腦圖時，科學家收集了 1.6PB 的數據——相當於 22 年不間斷的高清影片。

Scientists Map Miles of Wiring in a Speck of Mouse Brain

In charting a cubic millimeter of a mouse’s brain, scientists amassed 1.6 petabytes of data — the equivalent of 22 years of nonstop high-definition video.

A petabyte (PB) is a unit of measurement in computers and similar electronic devices. One petabyte holds 1000 terabytes (TB) or 1,000,000,000,000,000 bytes.

The Special Relationship Between America and Britain Is a Myth Despite Winston Churchill’s coining. Tibetans get high-altitude edge from extinct Denisovans' genes Britain has landed with a 10% sum on most of its goods exports to America, the lowest rate on offer in tariffs bingo. 西藏人高原基因來自於遠古滅絕人類

Britain has landed with a 10% sum on most of its goods exports to America, the lowest rate on offer in tariffs bingo. But serious pain may still be on its way



Of the relationship between America and the Britain, it’s been said “that the special relationship was special because only one side knew it existed,” writes the journalist Geoffrey Wheatcroft. “Is it too much to hope that the tired and foolish phrase might now be given a rest?"



nytimes.com
Opinion | The Special Relationship Between America and Britain Is a Myth
Despite Winston Churchill’s coining of th

Researchers have known for a while that many people alive today carry genes from human species other than Homo sapiens, the result of ancient interbreeding with Neanderthals and Denisovans. The specifics, though, have not been clear. But in one case they now are, for it is because of these occasional Denisovan ancestors that Tibetans thrive in Tibet http://econ.st/1j0IacI

讚

西藏人高原基因來自於遠古滅絕人類

更新時間 2014年7月3日, 格林尼治標準時間11:47

西藏人的高原基因來自於遠古已滅絕的人類

據《自然》期刊報告，現代人從遠古所繼承的一種基因，可以讓他們適應高原的生活。

據悉，這種遠古的人類已經滅絕。這種叫EPAS-1的基因變種可以影響人類血液中的氧氣，在西藏人當中十分普遍。

西藏人長年生活在海拔4000米的高原。

該DNA(脫氧核糖核酸)的序列與一種早已消失了的遠古人類丹尼索瓦人（Denisovans）的DNA相符合。

其實，包括我們自己在內的現代人類的許多人都攜帶已經滅絕了的遠古人類的DNA。

而這些遠古已滅絕的人類曾經和我們的非洲祖先「雜交」。

40萬年前出現的尼安德特人（the Neanderthals）曾生活在歐洲和西亞地區，直到3萬5千年前。

無論是尼安德特人還是丹尼索瓦人都對現代人的DNA有所貢獻。

而現在，研究人員通過研究血紅蛋白找到了EPAS-1基因與丹尼索瓦人之間的聯繫。

比如，當人體在海拔較高的高原時，體內血液中的氧氣水平就比較低，這時候EPAS-1基因就會告訴身體中的其他的基因活躍起來，包括生產額外的紅血球。

而這種EPAS-1基因的變體在西藏人中十分普遍，這可能和他們在數千年前移居到高原生活時所發生的一種自然的基因選擇。

明確證據

該文章的主要作者之一，加州大學的尼爾森教授說，他們找到了明確的證據這種基因來自丹尼索瓦人。

尼爾森告訴BBC，「如果你、我到海拔高緯度時，我們都將立即會經歷各種不同的不良身體反應。我們會喘氣困難，還可能會得高原病。」

「過一陣，我們的身體為了適應這一情況將會生產更多的紅血球。但是由於我們不適應高原環境，我們的身體可能將會製造許多紅血球。」

「我們的血液變得太粘稠，血壓也會升高，這樣就會有中風的危險，如果是孕婦還可能患妊娠毒血症」。

但西藏人就不會有這些問題，他們的身體不會製造過多的紅血球，因此血液也不會粘稠。

尼爾森教授的研究小組在2010年就發現了西藏人身體中的這種EPAS-1基因變體，但是研究人員當時無法解釋它為什麼與從其他現代人類身上找到的DNA序列不一樣。

因此，他們才從更遠古的人類染色體組序列當中去尋找答案。

研究人員把它同尼安德特人相比較，沒有找到匹配，但當同丹尼索瓦人比較時令人吃驚地找到了吻合。

尼爾森教授解釋說，人類祖先與丹尼索瓦人的「雜交」發生在很久以前。

而當西藏人的祖先移居到高原之後，丹尼索瓦人的DNA在他們的身體中產生了基因變體，並喜歡這種環境轉變。之後它便存在於今天大多數的西藏人身上。

尼爾森教授說，這是人類通過與遠古人類「雜交」後獲得的基因適應新環境的一種清楚和直接的例子。

編譯：凱露

Tibetans get high-altitude edge from extinct Denisovans' genes

The average elevation of Tibet is almost 15,000 feet above sea level. (Goh Chai Hin / AFP/Getty Images)

JULIA ROSEN

Scientific ResearchTibetScience

High in the Himalayas, an ancient gene helps Tibetans thrive at altitude

Denisovans are extinct, but their genes live on in Tibetans

Tibetans provide more proof that early humans mated with Neanderthals and Denisovans

Forget climbing Mt. Everest — for most humans, just eking out a living on the harsh Tibetan plateau is challenge enough. But Tibetan people have thrived there for thousands of years, and a new study says it's thanks to a genetic adaptation they inherited from an ancient human relative.

The study, published Wednesday in the journal Nature, identifies a long segment of DNA shared by the extinct people known as Denisovans and modern-day Tibetans. The segment contains the gene scientists think gives Tibetans a lung up over lowlanders at high altitudes.

Tibetan people possess a unique gene that makes them well-adapted to high-altitude life. This gene appears to have come from an extinct early human relative. (BGI)

No one knew the Denisovans ever roamed the Earth until four years ago, when scientists sequenced the DNA of a finger bone unearthed in a cave in the Altai Mountains of southern Siberia. The genome exhibited similarities to that of modern humans and our extinct Neanderthal relatives, but it was different enough to be considered a distinct species.

Like Neanderthals, Denisovans mated with their human contemporaries, scientists soon discovered. People of Melanesian descent who today inhabit Papua New Guinea share 5% of their genetic makeup with the Denisovans.

Now it appears that Tibetans can also trace part of their ancestry to this mysterious group.

lRelated

OPINION L.A.

Neanderthal DNA shows that man's family tree is decidedly gnarled

SEE ALL RELATED

8

In the new study, scientists collected blood samples from 40 Tibetans and sequenced more than 30,000 nucleotides on a segment of DNA containingEPAS1, the gene that makes Tibetans so well-suited for life at high altitude. Then the scientists compared that sequence with those of 1,000 individuals representing the 26 human populations in the Human Genome Diversity Panel. They found the high-altitude gene in only 2 of the 40 Han Chinese people in the panel and no one else.

“Natural selection by itself could not explain that pattern,” said Rasmus Nielsen, a computational biologist at UC Berkeley and an author of the study. “The DNA sequence was too different from anything else we saw in other populations.”

So they investigated whether the gene might have been imported from extinct Neanderthals or Denisovans, and, bingo, they found a match.

But how did the gene end up in the genome of modern Tibetans? The scientists used computer models to test two different hypotheses. Were Denisovans and Tibetans descended from a common ancestor that gave the gene to both? Or did humans acquire the gene by mating with Denisovans?

Related Story: DNA from Neanderthal toe reveals interbreeding among ancient species

Monte Morin

Early humans and Denisovans probably diverged around half a million years ago, and it’s very unlikely that the gene could be maintained in both populations for so long, Nielsen said.

“By the process of recombination, DNA segments become shorter and shorter and shorter,” he said. “But here we have a very long segment that is shared. That’s very unlikely, statistically.”

Alternatively, the gene could have entered the Tibetan gene pool more recently via sex. Once transferred, the gene would have spread rapidly in the Tibetan population because of the merciless selective pressures of high-altitude living.

“Genetically, Han Chinese and Tibetans are very similar throughout the genome,” Nielsen said. “But for this particular gene, they are extremely differentiated from each other, which is something you only see with very strong or very recent selection.”

cComments

• Iam tibetan and finally what we learn in our school during my days in india really shares similar conclusion. As we tibetan are descendent from cross breed between monkey(a compassionate male) and the female ogress who is relatively voilent in nature.
  SURFMEIN
  AT 3:22 AM JULY 03, 2014

ADD A COMMENTSEE ALL COMMENTS

1

The reason Tibetans need EPAS1 is that their mountainous home — a crease of buckled crust thrust upward by the tectonic collision of India and Asia — lies about 15,000 feet above sea level, on average. Up there, the air contains 40% less oxygen than it does at low elevations.

Although previous studies had identified the importance of EPAS1, scientists still don’t know exactly what the gene does. They know only that it leads to lower levels of hemoglobin — the oxygen-toting protein in blood — in Tibetans who live at high altitude compared with people from low elevations who have acclimatized.

“That may sound counterintuitive,” said Nielsen — after all, wouldn’t you want more oxygen, and thus, more hemoglobin to deliver it? But people without the gene tend “overreact” at altitude.

A gene called EPAS1 helps regulate hemoglobin levels in Tibetans. (BGI)

“As we acclimatize, we’ll start to produce a lot of red blood cells,” he said, speaking for himself and other non-Tibetans. Too many, in fact. “That will expose us to various diseases like hypertension, increased risk of stroke and preeclampsia. There are very negative fitness effects of having too many red blood cells, and the Tibetans avoid them.”

So how do Tibetans get more oxygen? Presumably they don’t, Nielsen said, and scientists are still trying to understand the physiological mechanisms that allow them to cope.

But one thing is now clear: They owe their extraordinary fitness to a rogue gene introduced into the human genome from their long-lost cousins.

Abigail Bigham, an anthropologist at the University of Michigan who was not involved in the study, said now the search for Denisovan DNA should extend to other groups not represented in the Human Genome Diversity Panel.

“When they looked in Han Chinese, they saw it in only two individuals,” Bigham said. “But other populations in Central Asia or East Asia — there are 49 other ethnic minorities in China that have different genetic backgrounds — would have been interesting to look at as well.”

In any case, she said, the new study adds to a growing body of work that has reshaped the way scientists think about human evolution and our relationship to our extinct relatives.

For a long time, most scientists believed Neanderthals and Denisovans had nothing to do with modern humans. Now they realize that these species are responsible for introducing some of the genetic diversity that allowed people to adapt to unique environments.

“We’ve come full circle,” Bigham said. “Not only has there been interbreeding, but in fact that interbreeding has led to important functional changes in the human genome.”

For all things science, follow me @ScienceJulia