/ x; X- D( W8 [5 H0 H 8 x1 \3 B" `3 o& m! KPhysicists have shed new light on one of the greatest mysteries in science: Why the Universe consists primarily of matter and not antimatter.9 Q6 g; [- s# y6 O4 x) K
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Antimatter is a shadowy mirror image of the ordinary matter we are familiar with.
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For the first time, scientists have measured the forces that make certain antimatter particles stick together.
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The findings, published in Nature, may yield clues to what led to the scarcity of antimatter in the cosmos today.
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The forces between antimatter particles - in this case antiprotons - had not been measured before. If antiprotons were found to behave in a different way to their "mirror images" (the ordinary proton particles that are found in atoms) it might provide a potential explanation for what is known as "matter/antimatter asymmetry".
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At the beginning of the Universe, the Big Bang produced matter and antimatter in equal amounts. But that's not the world we see today: instead antimatter is extremely rare.
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Some phenomenon must have led to the overwhelming dominance of matter; scientists have their theories, but the evidence remains elusive.
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"Although this puzzle has been known for decades and little clues have emerged, it remains one of the big challenges of science," said co-author Aihong Tang, from the Brookhaven National Laboratory in New York, US.
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"Anything we learn about the nature of antimatter can potentially contribute to solving this puzzle."
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* q# K+ }7 p9 n8 n0 V( o6 G3 x % K2 X" v- m4 o, b' y物理學(xué)家新近揭示科學(xué)界一大未解之謎：為什么宇宙主要由物質(zhì)組成,，而非反物質(zhì),。! e! J1 @! U" L: a% o
Thankfully, antimatter can be produced by particle accelerators - albeit in tiny amounts - giving scientists the opportunity to study its properties.
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Using a particle smasher called the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, physicists were able to measured the force of interaction between pairs of antiprotons.
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The scientists found that the force between antiproton pairs is attractive, just like the strong nuclear force that holds protons together within atoms.
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Antimatter particles have the same masses as their ordinary matter equivalents, but carry opposite charges.
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Zhengqiao Zhang, another scientist who studied the antiproton interactions using the RHIC, said: "We see lots of protons, the basic building blocks of conventional atoms, coming out, and we see almost equal numbers of antiprotons.
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"The antiprotons look just like familiar protons, but because they are antimatter, they have a negative charge instead of positive, so they curve the opposite way in the magnetic field of the detector."
Within the accuracy of these measurements, matter and antimatter appear to be perfectly symmetric. There didn't appear to be some asymmetric quirk of the strong force that could account for the continuing existence of matter in the Universe and the scarcity of antimatter.
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That points scientists towards other explanations for the matter/antimatter asymmetry. For example, neutrinos (another fundamental building block of the Universe) might be their own antiparticles. Differences in the way neutrino particles interacted after the Big Bang might have led to a slight matter excess that allowed our Universe to exist.
8 w5 ~" X1 W: R5 V感謝上帝，我們可以通過(guò)粒子加速器產(chǎn)生反物質(zhì)——盡管只有微量,，但這也提供了科學(xué)家們研究反物質(zhì)屬性的機(jī)會(huì),。 % S u0 ~1 n6 l9 _' o5 `" K% F+ |% g5 k: V: X, K ?& b' j
通過(guò)使用布魯克海文國(guó)家實(shí)驗(yàn)室被稱(chēng)為相對(duì)重離子碰撞機(jī)（RHIC）的粒子加速器，物理學(xué)家得以測(cè)定反質(zhì)子之間的作用力,。3 X) J* z/ G+ f+ D" O/ r5 K; O
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科學(xué)家發(fā)現(xiàn),，反質(zhì)子之間具有很強(qiáng)的吸引力，就像原子核內(nèi)質(zhì)子間的強(qiáng)核力,。% V* ~/ i. {6 T$ j* `% m/ A" ~/ K3 \
5 B9 O3 N/ i2 i# v反物質(zhì)粒子同正物質(zhì)具有相同的質(zhì)量,，但是卻攜帶相反的電荷。4 w" n% ]2 b2 v# L4 p# z R! N
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另一位在RHIC研究中的科學(xué)家——張正喬（估計(jì)是華裔）介紹說(shuō)：“我們看到的大量構(gòu)成基本原子的質(zhì)子飛出,，而這個(gè)量與觀測(cè)到的反質(zhì)子幾乎相等。反質(zhì)子就像我們熟悉的質(zhì)子,，但因?yàn)樗麄兪欠次镔|(zhì),，因此他們帶有一個(gè)單位的負(fù)電荷，而非正電荷,。因此,，他們?cè)诖艌?chǎng)檢測(cè)器重劃出相反的曲線�,！�8 ]3 _5 d, X |! }/ B. K$ L5 C: p: ~
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基于這些測(cè)量的精確性,，物質(zhì)和反物質(zhì)似乎是完全對(duì)稱(chēng)的。沒(méi)有絲毫與正物質(zhì)性質(zhì)完全相悖的轉(zhuǎn)折性證據(jù)可以解釋為什么宇宙中存在連續(xù)物質(zhì)而鮮有反物質(zhì),。 c) H) @2 j6 a* E; k
; `2 f. @0 y: F6 p原本理論物理界是認(rèn)為CP對(duì)稱(chēng)不能被嚴(yán)格遵守,，現(xiàn)在普遍傾向于CPT對(duì)稱(chēng)也是被破壞的,，C是反粒子共軛運(yùn)算，P是宇稱(chēng),，T是時(shí)間,，也就是說(shuō)，一個(gè)事物,，正反物質(zhì)左右手對(duì)稱(chēng)時(shí)間反演全部倒過(guò)來(lái)重來(lái)一次的話,，沒(méi)法做到嚴(yán)格對(duì)稱(chēng)3 Y/ Y, g2 a. P! o2 U4 @1 ~7 n
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所以，目前來(lái)看,，假定我們認(rèn)定帶負(fù)電的電子,，帶正點(diǎn)的質(zhì)子作為正物質(zhì)的話，自然界比較偏好正物質(zhì),，正是宇宙大爆炸時(shí)期這點(diǎn)微小的偏好,，留下了今天的所有物質(zhì)
