How we explore unanswered questions in physics

There is something about physics that has been really bothering me since I was a little kid. And it's related to a question that scientists have been asking for almost 100 years, with no answer. How do the smallest things in nature, the particles of the quantum world, match up with the largest things in nature -- planets and stars and galaxies held together by gravity?

As a kid, I would puzzle over questions just like this. I would fiddle around with microscopes and electromagnets, and I would read about the forces of the small and about quantum mechanics and I would marvel at how well that description matched up to our observation. Then I would look at the stars, and I would read about how well we understand gravity, and I would think surely, there must be some elegant way that these two systems match up. But there's not. And the books would say, yeah, we understand a lot about these two realms separately, but when we try to link them mathematically, everything breaks.

And for 100 years, none of our ideas as to how to solve this basically physics disaster, has ever been supported by evidence. And to little old me -- little, curious, skeptical James -- this was a supremely unsatisfying answer.

So, I'm still a skeptical little kid. Flash-forward now to December of 2015, when I found myself smack in the middle of the physics world being flipped on its head. It all started when we at CERN saw something intriguing in our data: a hint of a new particle, an inkling of a possibly extraordinary answer to this question.

So I'm still a skeptical little kid, I think, but I'm also now a particle hunter. I am a physicist at CERN's Large Hadron Collider, the largest science experiment ever mounted. It's a 27-kilometer tunnel on the border of France and Switzerland buried 100 meters underground. And in this tunnel, we use superconducting magnets colder than outer space to accelerate protons to almost the speed of light and slam them into each other millions of times per second, collecting the debris of these collisions to search for new, undiscovered fundamental particles. Its design and construction took decades of work by thousands of physicists from around the globe, and in the summer of 2015, we had been working tirelessly to switch on the LHC at the highest energy that humans have ever used in a collider experiment.

Now, higher energy is important because for particles, there is an equivalence between energy and particle mass, and mass is just a number put there by nature. To discover new particles, we need to reach these bigger numbers. And to do that, we have to build a bigger, higher energy collider, and the biggest, highest energy collider in the world is the Large Hadron Collider. And then, we collide protons quadrillions of times, and we collect this data very slowly, over months and months. And then new particles might show up in our data as bumps -- slight deviations from what you expect, little clusters of data points that make a smooth line not so smooth. For example, this bump, after months of data-taking in 2012, led to the discovery of the Higgs particle -- the Higgs boson -- and to a Nobel Prize for the confirmation of its existence.

This jump up in energy in 2015 represented the best chance that we as a species had ever had of discovering new particles -- new answers to these long-standing questions, because it was almost twice as much energy as we used when we discovered the Higgs boson. Many of my colleagues had been working their entire careers for this moment, and frankly, to little curious me, this was the moment I'd been waiting for my entire life. So 2015 was go time.

So June 2015, the LHC is switched back on. My colleagues and I held our breath and bit our fingernails, and then finally we saw the first proton collisions at this highest energy ever. Applause, champagne, celebration. This was a milestone for science, and we had no idea what we would find in this brand-new data. And then a few weeks later, we found a bump. It wasn't a very big bump, but it was big enough to make you raise your eyebrow. But on a scale of one to 10 for eyebrow raises, if 10 indicates that you've discovered a new particle, this eyebrow raise is about a four.

(Laughter)

I spent hours, days, weeks in secret meetings, arguing with my colleagues over this little bump, poking and prodding it with our most ruthless experimental sticks to see if it would withstand scrutiny. But even after months of working feverishly -- sleeping in our offices and not going home, candy bars for dinner, coffee by the bucketful -- physicists are machines for turning coffee into diagrams --

(Laughter)

This little bump would not go away. So after a few months, we presented our little bump to the world with a very clear message: this little bump is interesting but it's not definitive, so let's keep an eye on it as we take more data. So we were trying to be extremely cool about it. And the world ran with it anyway. The news loved it. People said it reminded them of the little bump that was shown on the way toward the Higgs boson discovery. Better than that, my theorist colleagues -- I love my theorist colleagues -- my theorist colleagues wrote 500 papers about this little bump.

(Laughter)

The world of particle physics had been flipped on its head. But what was it about this particular bump that caused thousands of physicists to collectively lose their cool? This little bump was unique. This little bump indicated that we were seeing an unexpectedly large number of collisions whose debris consisted of only two photons, two particles of light. And that's rare. Particle collisions are not like automobile collisions. They have different rules. When two particles collide at almost the speed of light, the quantum world takes over. And in the quantum world, these two particles can briefly create a new particle that lives for a tiny fraction of a second before splitting into other particles that hit our detector. Imagine a car collision where the two cars vanish upon impact, a bicycle appears in their place --

(Laughter)

And then that bicycle explodes into two skateboards, which hit our detector.

(Laughter)

Hopefully, not literally. They're very expensive.

Events where only two photons hit out detector are very rare. And because of the special quantum properties of photons, there's a very small number of possible new particles -- these mythical bicycles -- that can give birth to only two photons. But one of these options is huge, and it has to do with that long-standing question that bothered me as a tiny little kid, about gravity.

Gravity may seem super strong to you, but it's actually crazily weak compared to the other forces of nature. I can briefly beat gravity when I jump, but I can't pick a proton out of my hand. The strength of gravity compared to the other forces of nature? It's 10 to the minus 39. That's a decimal with 39 zeros after it.

Worse than that, all of the other known forces of nature are perfectly described by this thing we call the Standard Model, which is our current best description of nature at its smallest scales, and quite frankly, one of the most successful achievements of humankind -- except for gravity, which is absent from the Standard Model. It's crazy. It's almost as though most of gravity has gone missing. We feel a little bit of it, but where's the rest of it? No one knows.

But one theoretical explanation proposes a wild solution. You and I -- even you in the back -- we live in three dimensions of space. I hope that's a non-controversial statement.

(Laughter)

All of the known particles also live in three dimensions of space. In fact, a particle is just another name for an excitation in a three-dimensional field; a localized wobbling in space. More importantly, all the math that we use to describe all this stuff assumes that there are only three dimensions of space. But math is math, and we can play around with our math however we want. And people have been playing around with extra dimensions of space for a very long time, but it's always been an abstract mathematical concept. I mean, just look around you -- you at the back, look around -- there's clearly only three dimensions of space.

But what if that's not true? What if the missing gravity is leaking into an extra-spatial dimension that's invisible to you and I? What if gravity is just as strong as the other forces if you were to view it in this extra-spatial dimension, and what you and I experience is a tiny slice of gravity make it seem very weak? If this were true, we would have to expand our Standard Model of particles to include an extra particle, a hyperdimensional particle of gravity, a special graviton that lives in extra-spatial dimensions.

I see the looks on your faces. You should be asking me the question, "How in the world are we going to test this crazy, science fiction idea, stuck as we are in three dimensions?" The way we always do, by slamming together two protons --

(Laughter)

Hard enough that the collision reverberates into any extra-spatial dimensions that might be there, momentarily creating this hyperdimensional graviton that then snaps back into the three dimensions of the LHC and spits off two photons, two particles of light. And this hypothetical, extra-dimensional graviton is one of the only possible, hypothetical new particles that has the special quantum properties that could give birth to our little, two-photon bump.

So, the possibility of explaining the mysteries of gravity and of discovering extra dimensions of space -- perhaps now you get a sense as to why thousands of physics geeks collectively lost their cool over our little, two-photon bump. A discovery of this type would rewrite the textbooks. But remember, the message from us experimentalists that actually were doing this work at the time, was very clear: we need more data. With more data, the little bump will either turn into a nice, crisp Nobel Prize --

(Laughter)

Or the extra data will fill in the space around the bump and turn it into a nice, smooth line.

So we took more data, and with five times the data, several months later, our little bump turned into a smooth line. The news reported on a "huge disappointment," on "faded hopes," and on particle physicists "being sad." Given the tone of the coverage, you'd think that we had decided to shut down the LHC and go home.

(Laughter)

But that's not what we did. But why not? I mean, if I didn't discover a particle -- and I didn't -- if I didn't discover a particle, why am I here talking to you? Why didn't I just hang my head in shame and go home?

Particle physicists are explorers. And very much of what we do is cartography. Let me put it this way: forget about the LHC for a second. Imagine you are a space explorer arriving at a distant planet, searching for aliens. What is your first task? To immediately orbit the planet, land, take a quick look around for any big, obvious signs of life, and report back to home base. That's the stage we're at now. We took a first look at the LHC for any new, big, obvious-to-spot particles, and we can report that there are none. We saw a weird-looking alien bump on a distant mountain, but once we got closer, we saw it was a rock.

But then what do we do? Do we just give up and fly away? Absolutely not; we would be terrible scientists if we did. No, we spend the next couple of decades exploring, mapping out the territory, sifting through the sand with a fine instrument, peeking under every stone, drilling under the surface. New particles can either show up immediately as big, obvious-to-spot bumps, or they can only reveal themselves after years of data taking.

Humanity has just begun its exploration at the LHC at this big high energy, and we have much searching to do. But what if, even after 10 or 20 years, we still find no new particles? We build a bigger machine.

(Laughter)

We search at higher energies. We search at higher energies. Planning is already underway for a 100-kilometer tunnel that will collide particles at 10 times the energy of the LHC. We don't decide where nature places new particles. We only decide to keep exploring. But what if, even after a 100-kilometer tunnel or a 500-kilometer tunnel or a 10,000-kilometer collider floating in space between the Earth and the Moon, we still find no new particles? Then perhaps we're doing particle physics wrong.

(Laughter)

Perhaps we need to rethink things. Maybe we need more resources, technology, expertise than what we currently have. We already use artificial intelligence and machine learning techniques in parts of the LHC, but imagine designing a particle physics experiment using such sophisticated algorithms that it could teach itself to discover a hyperdimensional graviton.

But what if? What if the ultimate question: What if even artificial intelligence can't help us answer our questions? What if these open questions, for centuries, are destined to be unanswered for the foreseeable future? What if the stuff that's bothered me since I was a little kid is destined to be unanswered in my lifetime? Then that ... will be even more fascinating.

We will be forced to think in completely new ways. We'll have to go back to our assumptions, and determine if there was a flaw somewhere. And we'll need to encourage more people to join us in studying science since we need fresh eyes on these century-old problems. I don't have the answers, and I'm still searching for them. But someone -- maybe she's in school right now, maybe she's not even born yet -- could eventually guide us to see physics in a completely new way, and to point out that perhaps we're just asking the wrong questions. Which would not be the end of physics, but a novel beginning.

Thank you.

最后編輯于
?著作權(quán)歸作者所有,轉(zhuǎn)載或內(nèi)容合作請聯(lián)系作者
  • 序言:七十年代末侵续,一起剝皮案震驚了整個濱河市,隨后出現(xiàn)的幾起案子谓松,更是在濱河造成了極大的恐慌,老刑警劉巖苞氮,帶你破解...
    沈念sama閱讀 222,946評論 6 518
  • 序言:濱河連續(xù)發(fā)生了三起死亡事件舷夺,死亡現(xiàn)場離奇詭異猖辫,居然都是意外死亡,警方通過查閱死者的電腦和手機(jī)伍宦,發(fā)現(xiàn)死者居然都...
    沈念sama閱讀 95,336評論 3 399
  • 文/潘曉璐 我一進(jìn)店門芽死,熙熙樓的掌柜王于貴愁眉苦臉地迎上來,“玉大人次洼,你說我怎么就攤上這事关贵。” “怎么了卖毁?”我有些...
    開封第一講書人閱讀 169,716評論 0 364
  • 文/不壞的土叔 我叫張陵揖曾,是天一觀的道長。 經(jīng)常有香客問我亥啦,道長炭剪,這世上最難降的妖魔是什么? 我笑而不...
    開封第一講書人閱讀 60,222評論 1 300
  • 正文 為了忘掉前任翔脱,我火速辦了婚禮奴拦,結(jié)果婚禮上,老公的妹妹穿的比我還像新娘届吁。我一直安慰自己错妖,他們只是感情好,可當(dāng)我...
    茶點(diǎn)故事閱讀 69,223評論 6 398
  • 文/花漫 我一把揭開白布疚沐。 她就那樣靜靜地躺著暂氯,像睡著了一般。 火紅的嫁衣襯著肌膚如雪濒旦。 梳的紋絲不亂的頭發(fā)上,一...
    開封第一講書人閱讀 52,807評論 1 314
  • 那天再登,我揣著相機(jī)與錄音尔邓,去河邊找鬼晾剖。 笑死,一個胖子當(dāng)著我的面吹牛梯嗽,可吹牛的內(nèi)容都是我干的齿尽。 我是一名探鬼主播,決...
    沈念sama閱讀 41,235評論 3 424
  • 文/蒼蘭香墨 我猛地睜開眼灯节,長吁一口氣:“原來是場噩夢啊……” “哼循头!你這毒婦竟也來了?” 一聲冷哼從身側(cè)響起炎疆,我...
    開封第一講書人閱讀 40,189評論 0 277
  • 序言:老撾萬榮一對情侶失蹤卡骂,失蹤者是張志新(化名)和其女友劉穎,沒想到半個月后形入,有當(dāng)?shù)厝嗽跇淞掷锇l(fā)現(xiàn)了一具尸體全跨,經(jīng)...
    沈念sama閱讀 46,712評論 1 320
  • 正文 獨(dú)居荒郊野嶺守林人離奇死亡,尸身上長有42處帶血的膿包…… 初始之章·張勛 以下內(nèi)容為張勛視角 年9月15日...
    茶點(diǎn)故事閱讀 38,775評論 3 343
  • 正文 我和宋清朗相戀三年亿遂,在試婚紗的時候發(fā)現(xiàn)自己被綠了浓若。 大學(xué)時的朋友給我發(fā)了我未婚夫和他白月光在一起吃飯的照片。...
    茶點(diǎn)故事閱讀 40,926評論 1 353
  • 序言:一個原本活蹦亂跳的男人離奇死亡蛇数,死狀恐怖挪钓,靈堂內(nèi)的尸體忽然破棺而出,到底是詐尸還是另有隱情耳舅,我是刑警寧澤碌上,帶...
    沈念sama閱讀 36,580評論 5 351
  • 正文 年R本政府宣布,位于F島的核電站挽放,受9級特大地震影響绍赛,放射性物質(zhì)發(fā)生泄漏。R本人自食惡果不足惜辑畦,卻給世界環(huán)境...
    茶點(diǎn)故事閱讀 42,259評論 3 336
  • 文/蒙蒙 一吗蚌、第九天 我趴在偏房一處隱蔽的房頂上張望。 院中可真熱鬧纯出,春花似錦蚯妇、人聲如沸。這莊子的主人今日做“春日...
    開封第一講書人閱讀 32,750評論 0 25
  • 文/蒼蘭香墨 我抬頭看了看天上的太陽。三九已至焕襟,卻和暖如春陨收,著一層夾襖步出監(jiān)牢的瞬間,已是汗流浹背。 一陣腳步聲響...
    開封第一講書人閱讀 33,867評論 1 274
  • 我被黑心中介騙來泰國打工务漩, 沒想到剛下飛機(jī)就差點(diǎn)兒被人妖公主榨干…… 1. 我叫王不留拄衰,地道東北人。 一個月前我還...
    沈念sama閱讀 49,368評論 3 379
  • 正文 我出身青樓饵骨,卻偏偏與公主長得像翘悉,于是被迫代替她去往敵國和親。 傳聞我的和親對象是個殘疾皇子居触,可洞房花燭夜當(dāng)晚...
    茶點(diǎn)故事閱讀 45,930評論 2 361

推薦閱讀更多精彩內(nèi)容

  • **2014真題Directions:Read the following text. Choose the be...
    又是夜半驚坐起閱讀 9,590評論 0 23
  • 喜歡這樣暖陽里的盎然春色妖混,就算生活再無趣,只要想到軟創(chuàng)園內(nèi)的那片湖轮洋,從inovatio天臺上遠(yuǎn)眺所見的連綿青山制市,每...
    ece3e923baf3閱讀 529評論 0 1
  • 吃一頓用心烹飪的飯 聽一首輕快簡單的歌 將房間整理得干凈整潔 一個人泡澡 一個人看書 一個人旅行 收拾好泛濫的小情...
    如煙魚閱讀 245評論 3 4
  • 01. 在這個急劇變化和發(fā)展時代息堂,讀書不再是一種情懷,而是一種必備的生存技能块促。 不愛讀書荣堰,不會讀書的人,會像在馬拉...
    楊楓先生閱讀 1,759評論 4 50