Of Particular Significance

Some Good Reads

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 04/26/2012

I’m preparing an article on a very important type of energy that I’ve avoided writing about so far — the energy that comes from the interaction among fields.  I’ve avoided it because it’s tricky to figure out how to explain it.  But it’s important, for this form of energy is responsible for all the structure in the universe, from atoms to galaxies.  The article’s not quite ready yet, so today I’ve just got some good reading material for you, including the heavy, the weird, the amusing, and the optimistic.

Heavy stuff first: from the Nobel Laureate and writer Steven Weinberg, who among many many contributions to particle physics, cosmology and quantum field theory is co-inventor of the modern theory of the weak nuclear force and how it ties in with the electromagnetic force (`the electroweak theory’).  He has written an article in the New York Review of Books called `The Crisis of Big Science.  If you don’t understand that large scientific enterprises, such as are needed in modern particle physics, astrophysics and cosmology, are under serious threat, or you don’t know why they are, you need to read this article.  Every particle physicist, string theorist, astrophysicist and cosmologist needs to read it.  (Though I should add that in his brief explanation of the Standard Model of particle physics, Weinberg takes some misleading shortcuts typical of the old guard explanation style, and which this website avoids.  See if you can find them!)

Now, the weird — yes, quantum mechanics, relativity and causality.  According to the equations of quantum mechanics, the way in which reality is organized in our quantum world is so bizarre that it lies beyond human imagination.  But hey, a new experiment seems to confirm (to no one’s surprise, but to the discomfort of many) that some of the weirdest predictions really happen. (A caveat first; I am not an expert in these types of measurements and cannot determine myself whether the measurement is reliable, so you may want to wait for a confirming experiment.)  http://arstechnica.com/science/news/2012/04/decision-to-entangle-effects-results-of-measurements-taken-beforehand.ars  Information about physical systems is, in some sense, stored in a distributed fashion, not entirely locally.  Yet despite this, no information is transferred faster than light, and the basic requirements of relativity and causality are (just barely!) respected.  If you want to understand something about the types of theoretical and conceptual issues that experiments like this are inspired by, I recommend a technical lecture by the great Harvard professor Sidney Coleman, called Quantum Mechanics IN YOUR FACE.

On the light-hearted side, my alma mater Simon’s Rock has just been rated as one of the ten top nerdiest colleges in the United States by the Princeton Review.  Wow, a college where you actually have small classes, talk to your professors, and really learn stuff! Honestly, they’re just saying that Rockers aren’t so big on sports and some (not me though) play a lot of things like Dungeons and Dragons.  Whatever… we know these lists are pretty arbitrary, but hey, I’m amused.

And for more general entertainment, my friend Professor Daniel Whiteson (of the University of California at Irvine, and of the CDF and ATLAS experiments at the Tevatron and the Large Hadron Collider) requests that I point you to the efforts that he and his collaborators are making to educate and amuse you: two accessible comic strips in video form, one on the Higgs particle and the ongoing search for it, and one on dark matter.

Finally, a worthwhile post from the Resonaances blog, explaining some of the speculative ideas by theorists that are in the process of being falsified by the data at the Large Hadron Collider.  It’s a good post, but I have to add a caution: What he says is correct assuming the hints of a Higgs particle at a mass of 125 GeV (see here and here for more recent updates) really turn out to be the real thing.  You see, Resonaances’ author is convinced not only that the Higgs particle has been definitively discovered but also that all other physicists (except me) are as convinced as he is.  So he just writes as though the case is settled.   I suggest you follow Weinberg and remain more circumspect; better evidence than this has vanished in the past.

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20 Responses

  1. Hello Prof Strassler,

    Thanks for the interesting articles and the link to the talk of Sidney Coleman!
    I also understood the EPR paradox for the first time from David Mermin’s article and was surprised to hear that the great Sidney Coleman learned it this way also.

    After the experimental confirmation of the EPR paradox through Bell’s inequality by Alain Aspect, it is now time to change the final conclusion of the article from:

    Nevertheless, this experiment provides a realization of one of the fundamental paradoxes of quantum mechanics: that measurements taken at different points in space and time appear to affect each other, even though there is no mechanism that allows information to travel between them.


    This experiment provides a realization of one of the fundamental principles of quantum mechanics: that measurements taken at space-like separated points can affect each other but no mechanism allows information to travel between them (faster than the speed of light).

    What do you think? Thanks again!

  2. I just sketched the Alice-Bob-Victor light cones. If Alice encrypts after Victor observes, she may encrypt outside of the light cone of Victor’s observation. This is the paradox. But, further on, Bob receives the message and uses his entangled object to decrypt, and this Must occur in the light cone of Victor’s observation. (This assumes Alice, Bob and Victor remain stationary.)

    I don’t see any “faster than light” spookiness going on between Victor and Bob, since the message appears to Bob in Victor’s cone.

    What I think is intersting, is how does anyone know whether Bob received the message without talking to Alice? Doesn’t the uncertainty kind of extend out to where the light cone of Bob’s receipt reaches Alice? Until the received message can be compared with the sent message, who knows whether it was received at all?

    1. Sorry, but are you talking about something different from the Ars Technica article Matt linked to? That article says nothing about encrypting or decrypting, or about Bob receiving a message from Alice. And it says that Victor makes his measurement after Alice and Bob have made theirs.

  3. I think part of the sequence is that the first observation of one entangled object determines the state of both/all objects. In the Alice/Bob/Victor experiment, Victor was the first observer, but his observation took place after everyone had received their entangled objects.

    The counterintuitive sequence is to receive the object before it state is determined. Once we get our brains wrapped around our ability to receive something that might “change” before we look at it, there’s no paradox. (Except it doesn’t really change. Thats oldspeak.)

    1. Hi Greg,

      I assume you’re not asking why things happen the way they happen, but rather you want a presentation of the experiment with more familiar objects (objects from day to day experience) instead of photons. If I got it wrong, I apologize. Assuming I understood your question right, let me give you my take on it. I’m just a layman, so I won’t say I’m giving you an answer because I might be completely wrong. I’m just telling you how I “see” this experiment in my head using tennis balls instead of photons.

      To understand the experiment conceptually, you don’t even need three people. Alice and Victor are enough (I will tell you at the end why do you need three people in real life).

      Another thing is that you shouldn’t imagine yourself as a third party observer of the experiment, as there’s no such ting in real life. Instead you should imagine you’re one of the persons in the experiment. Let’s say you are Victor.

      So we have a special tennis ball machine that throws two balls in the same time, in opposite directions, instead of just one ball. This machine is full of red and blue tennis balls, so it can throw either blue or red balls in any of the two directions. But there’s one particularity about the machine. It cannot throw the same color in the same time in both directions. If it throws a red ball in one direction it will throw a blue ball in the other direction. OK we have the source of balls now 🙂

      Imagine now that at one end of the machine, about 100 meters (or yards if you prefer) away stays Alice. You (Victor) stay at the other end of the machine, but much further away (Let’s say at the other end of the city). Now the machine throws one ball in each direction. Alice will receive her ball first and write down it’s color. You (Victor) don’t know what color Alice wrote down. A bit later your ball arrives. Attention, now you have to imagine something that cannot happen with real objects: Imagine that exactly in the moment your ball hits you, you can decide what color your ball should have. You cannot decide this earlier. So, let’s say when the ball hits you, you decide the ball should be blue. Now because your ball is blue, Alice’s one should be red. And of course when you call Alice, she confirms she received a red ball. But remember, Alice wrote down the color of her ball before your ball arrived to you, and before you had the chance to decide what color your ball should have. People wonder “How the heck Alice’s ball knew to be red before you had the chance to decide that your ball should be blue?” Or equivalent “How the heck a thing that happened in the past (Alice’s ball was red) is somehow dependent on some future event (You deciding your ball should be blue)?” And this is the experiment.

      I can tell you about a couple of problems that arise because we used these weird tennis balls instead of photons (I’m calling them weird because we said you can decide the color of the ball when it arrives to you):

      First, one can ask why Alice, after receiving her ball, is not giving a quick call (before Victor’s ball arrives) to Victor to tell him about the color of her ball. Well, this cannot happen with photons because nothing can travel faster than photons. Not even a phone call 🙂 That’s why people say the causality is “barely” not broken.

      The second problem is that you can ask “What is so special about Victor? “Why can’t Alice decide the color of her ball when it arrives too?” In real life you cannot decide the color of your ball. If just one ball arrives to you, you can’t do anything about it. But what you can do in the quantum world, is if you receive two balls instead of one, you still cannot decide their color, but you can decide one thing: You can say “The two balls should not have the same color” Attention, you CANNOT say the opposite “The two balls should have the same color”. You can verify this generates no problem. Let’s put two tennis ball machines to fire towards you (Victor) and Alice, Alice, because she is closer to the machines receives her balls first and she is free to say “These two balls should not have the same color” and if she does it, this works fine for you too. In this case if you do nothing you receive two balls of different colors. You are still free to say ” The two balls should not have the same color” when they arrive and you still get two balls of different colors. No problem here. 🙂

      Now to make sure you’re in charge and only you can make decisions, you make sure only you receive two balls. At the other end you send only one ball to Alice and you call your friend Bob to receive the other ball. Other than that the experiment works as described above. The two tennis ball machines fire just once (and at once). Because they are closer to the machines, Alice and Bob receive their balls first and write down the colors. Then, when the two balls arrive to you, let’s say you decide to say “The balls shouldn’t have the same color”. Then you call Alice and Bob and they confirm to you each received a ball of different color. This is it (or at east the important part of it) 🙂

      Again, I might have gotten the things completely wrong. I’m waiting for Matt’s answer with great interest.

  4. “..the weirdest predictions really happen”

    quote from Matthew Francis article at Ars Technica.
    “this experiment provides a realization of one of the fundamental paradoxes of quantum mechanics: that measurements taken at different points in space and time appear to affect each other, even though there is no mechanism that allows information to travel between them.”

    Or perhaps that should be no *known* mechanism?
    We measure “Information” via photons transmitted between particles.
    Their finite speed governs our notion of causality.

    But what if each state change within 3-dimensional space is correlated to a state-change on a 2-d cosmic horizon?
    Then, what we perceive of as “particles”, are in fact extended objects (or maybe one extended object).

    The mechanism whereby non-local events occur is unknown (and maybe unknowable), because it’s governed a structure somewhere at the Planck scale.
    It plays no direct part in our common sense view of the world.
    But probe a bit deeper and its effects become apparent.

    1. You’re in some danger of mixing apples and oranges here — these are very complex issues that cannot be addressed without extreme care, and not in a single comment. But the issues surely don’t have to do with the Planck scale.

      1. No doubt!
        But one way to visualise this might be that Feynmann paths represent physical objects in 4-d space-time. (as is suggested by Khovanov homology)

    1. Remember to distinguish:
      1) a definitive confirmation of the non-existence of a STANDARD MODEL Higgs particle (2012)
      2) a definitive confirmation of the non-existence of ANY TYPE of Higgs particle (2020 or so?)

  5. I diagrammed the quantum crypto experiment, which led me to go back and verify that Victor has to make his observation before Alice encrypts (and, of course, before Bob decrypts, or vice versa). I wonder how long before? I went and reviewed some articles, and found that the sequence must be made of “time-like” intervals and not “space-like” intervals.
    That was when I STARTED to understand, a little.
    Is it true that Victor must observe before Alice does? How much sooner?

  6. Hi
    Quantum mechanics is so wierd. i read that article u posted a link for and i was woundering…if victor delayed his descion long enough for bob and alice to report thier results and then he makes a contradictionary choice…what would happen. the problem is victor would have to store the two photons without making any measurement somehow to allow time for bobs and alices results to arrive

  7. Dear friend and professor Matt. : whenever you are presented with a Q. and you do not answer , does that mean there is no scientific one ? ….for ex.
    1- What is the physical independent meaning of mass without reference to energy ?
    2- same for energy without reference to mass ?
    3- same for charge without reference to interactions ?
    I am here looking for the “pure” physical meaning , i asked this before , is lack of response means there is no scientific answer as we reached the most fundamental core of the phenomena ?

    1. These are not easy questions to answer because they are not entirely well-posed, and because they are difficult to rephrase and then answer in English without equations. I’ll try to get back to these at some point, but I can’t answer them directly. This week’s just too busy in any case… sorry, two lectures left to prepare for the weekend.

  8. Physics is pridefully dismissive of physical chirality, an emergent observable. Real world mirror symmetry falsifications are post hoc ergo propter hoc-inserted symmetry breakings. Observe the measurable alternative. The worst it can do is succeed.

    1. You’ve made your point now six times. It doesn’t make any sense, and you insult me and my field on my website, which isn’t very intelligent. Please stop.

      1. Uh oh, Matt. Uncle Al has discovered your blog. Get ready for an endless stream of rants about chirality and eotvos, written in a bizarre staccato phrasing. He’s been doing this since Usenet.

        I thought he was safely out of the way at Sabine’s blog (she seems to tolerate him – he’s been banned nearly everywhere else), but he seems to have escaped…

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