Is the Moon in the sky when you’re not looking?

If you find quantum physics hard to understand (or accept), rest assured that you are not alone. Even many physicists (including Albert Einstein, one of its founding fathers) refused to acknowledge that our world can behave so strangely. That atoms or electrons can be at two places at once or that it does not always make sense to talk about properties of particles before they are measured.

Physicists are also only people. When a new theory challenges our worldview, we start to look for mistakes in said theory and not in our assumptions about the universe. Many physical theories had to fight against ingrained beliefs — heliocentric model of the Solar system, Einstein’s special and general relativity, or quantum mechanics are just a few examples. Eventually, the theory prevails, at least until it is replaced by a new, more precise one.

In quantum physics, the assumptions of locality and realism are challenged. The locality assumption — which comes from special relativity — tells us that all information can travel through the universe only at the speed of light and not faster. When we assume realism, we assume that the outcome of a measurement exists already before the measurement is performed. In other words, if I look at the thermometer to find out how warm the weather is today, the temperature is not decided the moment I look at the thermometer; the air has this temperature independent of me looking at the thermometer.

Let’s illustrate that on an example. Suppose I have two coins with a very peculiar link between them. Every time I flip these coins, I get opposite outcomes. If the first coin shows heads, the other one shows tails and vice versa. I never know which coin will give which outcome but whenever I look at one coin, I immediately know what the outcome of the toss of the second coin will be.

So far so good. Now, I will take one of the coins and fly to the Moon while leaving you with the second coin here on Earth. If we now flip our coins at the same time, I immediately know what the outcome of your toss is, and you know the outcome of mine.

What does that have to do with local realism? Since we are now about 400 000 km apart, it takes any information about 1.3 seconds to travel between us. My coin thus cannot know what the outcome of your toss is; similarly, your coin knows nothing about my toss. That is what the locality assumption tells us.

How do the coins know what side up to end to always give opposite outcomes? That’s where the realism comes in. In this situation, it tells us that the result of the measurement has existed before the toss and both coins therefore know what outcome the toss is supposed to give.

This is how anyone should expect two such coins to behave. But if the coins obey the laws of quantum mechanics, things are different. We cannot say that the outcome of the toss exists before we actually toss them. (This is actually a matter of interpretation of quantum physics — it is generally assumed that the measurement outcome is decided the moment the measurement is performed.) That’s why some physicists claimed quantum physics must be incomplete — there must be some underlying theory that explains what outcome every single coin flip will give. And such a theory must be local and realistic.1

What should we believe? Local realism or quantum physics? It turns out there is a simple test for that. Suppose that instead of a pair of coins we have two such pairs and I take one coin of each pair to the Moon and keep the other two coins here with you. If we now both flip coins from the same pair, we will always get opposite outcomes. But if we flip coins from different pairs, any combination of outcomes is possible.

While the experiment with a single pair of coins was largely a matter of interpretation, with two pairs of coins do local realism and quantum physics predict different results. All we have to do is toss the coins many times, each of us deciding randomly which of the two coins to toss each round and then writing down which coin we tossed and what the outcome was. Then, we can compare our data and see which of the two theories is right.2

Although the test of local realism is, in principle, rather simple, it is not easy to build an experiment that can confidently decide whether local realism is true or not. There are two main challenges that need to be solved: The first problem is to make sure that the two systems are spatially separated. Here, it is important that the time difference between the measurements is so small that no communication between the two sites at the speed of light is possible. Since the distance over which quantum systems can be reliably transmitted is strongly limited, there are strict requirements on the synchronisation and speed of the experiment.

The second main problem is an efficient measurement. Most experimental tests of local realism are done with single photons but it is extremely difficult to detect those. The efficiency is so low that often detectors do not notice when a photon arrives. This opens a loophole — the measurement does not grant us access to the whole statistics but only to its part. And we cannot be sure that the statistics of the sub-ensemble is the same as that of the whole ensemble.

It took over 30 years to build an experiment (more precisely, three experiments; one with electron spins and two more with photons) that really confidently refute local realism and show that quantum mechanics has to be taken seriously. One of our basic assumptions about this world thus has to be wrong; some signals are able to travel faster than light or it does not make sense to talk about objects we are not currently observing.


1 The experiment with two coins and the conclusion in this paragraph are a simplified version of the famous EPR paradox. It was formulated by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935 to show the problems of the Copenhagen interpretation of quantum mechanics.

2 Such an experiment — not with coins but with electron spins — was first proposed by John Stewart Bell in 1964. He showed that a particular correlation between the spins is bounded by the value of 2 for local realistic theories, whereas quantum mechanics allows to have stronger correlations, with values exceeding 2.

 

What I learned (and didn’t) from a year of blogging

It has been a year since I started blogging. It did not go quite as well as I hoped it would but also not as badly as I was afraid it might. I started full of determination with a clear plan, wrote posts… and then stopped. It took me seven months to start again and since then, I have been writing regularly.

This is a good time to stop, take a deep breath, and look back. Analyse (I am a theoretical physicist, remember?) what I did well and what could have been better. Who knows, other bloggers (whether just starting or more experienced) might find this useful.

  1. Regularity
    It is easier to keep momentum than gain it; it is easier to lose momentum than keep it. It takes no effort to decide to write the next post later. When I momentarily have too much work to do, it seems reasonable to skip writing the next blog post. But if that happens, it becomes more difficult to write it. If I make it my priority to publish a post every week, I will. It is not always easy but it can be done.
  2. Planning and serendipity
    While it is a good idea to have a plan, one should never be too strict about sticking to it. Reacting to current affairs (if they are related to the topic of the blog) is a good way to reach new audiences. And being open to other impulses can inspire upcoming posts.
  3. Learning
    Keeping a blog about science is a constant learning process. I do not write about things that are completely new and unknown to me, of course, but I do need to make sure that everything is factually correct. What’s more, I need to make sure that the topic is understandable to non-physicists. For that, I have to consider several ways to look at a particular problem and pick the one (the ones) that is (or are) the easiest to comprehend. And I can always learn something new from that!
  4. Time
    It takes a lot of time to write a blog post. Writing a thousand words can be done fairly quickly; finding those words is a different matter entirely. A completely new blog post starts with a topic and an outline. I can think about those while doing other things (such as commuting to and from work) but they still need time. Then comes the draft, editing and proofreading. After that, I might need to prepare pictures and only then is a new post ready to be published. Without proper planning, it is impossible to get the next post out on time.
  5. Failure
    Sometimes, blog posts don’t turn out the way I was hoping. Maybe I didn’t have enough time for writing or I chose a difficult topic to write about. That happens. I can’t expect every post (or any post) to be perfect; some are better, some are worse. If I don’t want to write bad blog posts, the best strategy is to not write at all — and that’s not an option. As long as I can figure out what I did wrong and learn from it, everything is good.

Those are things I learned so far. But there are also things I am still struggling with and need to improve:

  1. Organisation
    It happens to me sometimes that I outline a blog post in my head and, before I write the post, I forget how I wanted to structure the argument. Then, I have to try and remember what I wanted to write or, in the worst case, start again from scratch. One way or the other, it costs me time. I need to learn to write these ideas down before they can flee. Or even better, make outlining part of the process of writing a draft, experiment with the outline and choose one that works the best.
  2. Finding time to write
    As I said above, writing a blog post takes time which is sometimes hard to find. There is a way out of this problem (at least partially):  Using any narrow time windows during the day to write. I just have to remember the next time I have few minutes free to take my notebook out (yes, I draft my blog posts by hand) and start writing.
  3. Writing ahead
    So far, I start writing the next post after I published the previous one. Does that sound reasonable? It isn’t, really. It means that I have exactly one week to write the next post. If I had several posts ready, I could occasionally take a little longer to write the next post — or even take a break for a week. Having a buffer is something I can start right away; all I need to do is be a little more strict about writing for the next few weeks and I will surely manage more than a post per week.

These are my experiences with blogging so far. If you also blog, what do you (or did you) struggle with? What helped you solve your problems?

The end is nigh. Well, not really

It is beginning. Earlier this week, I downloaded Scrivener and yesterday, I started outlining my dissertation. I still have a lot of time to finish — I am currently planning to submit early next year and defend in spring, though that might change — but I think it is a good idea to start now. Why, you ask?

Screenshot 2016-02-10 15.42.23
The dreaded blank page.

First of all, this is the longest, most complex piece of writing I ever set out to write. Sure, I had to write a bachelor and a master thesis but those two combined are probably shorter than my dissertation will be. It will therefore take more time to write. And it is better to start early and have plenty of time for edits than be chased by deadlines.

But more importantly — and perhaps paradoxically — I am starting to write now because I am not done researching yet. Just recently, I finished a project and am about to start a new one. What will I do? I DON’T KNOW. And that is exactly my point. This is the right moment for me to stop working on my own projects and publications and look systematically and in detail at the work of others. Then, I can better judge which open questions I can tackle. And it is only natural to write what I learn and turn it into the introductory parts of my dissertation.

Connected to both these reasons to start so early is a third one: Because not all my work is done and because the writing will be so complex, I need not only to write what I intend to but, first of all, figure out what it is that I want to write. And for that, I need to keep track of all thoughts and ideas that come to me and organise all the material I plan to use. This is a task that goes beyond what standard LaTeX editors (I used to date) can do. Therefore, I need to find a platform that can take care of that and become sufficiently familiar with it.

So far, Scrivener seems to be a good choice to do that. Not only can I use it to work on my draft but it also helps me to keep any notes and further materials at the same place as the dissertation draft. I have to look into it in more detail to find out how to best use all these features and that will need quite some time. But if all goes as smoothly as it seems it will, the writing itself will then be relatively easy.

Since I started so recently, I did not manage more than briefly outline the first half of my dissertation. And yet, it already helped me realise how much I still do not know about the basics that will form the foundations of my dissertation. If that happened with a deadline looming above me, it would mean a serious complication to my plans. Now, I can simply go and read on the stuff I still need to learn.

Quite naturally, this approach also has its disadvantages. How am I supposed to write the introductory chapters presenting the knowledge I am building upon if I still do not know what I will do during the last year of my PhD? My choice of the next project is simply constrained by that. This situation is not that much different from what I would experience anyway — my next project should, in some way, be related to my previous one. I might then need to rearrange the introductory material a little but it should not need any complicated redrafting.

In the end, this approach will probably save me a lot of binge writing. By the time my last research project is done, I will have, ideally, written most of my dissertation already; it will only remain to write about my last project and make sure the whole text is coherent. Finishing my dissertation will then be just a matter of a few weeks and not several months.

And now, if you’ll excuse me, I have some writing to do…

Good scientists publish, shitty ones blog. Or do they?

As scientists, we are in a very privileged position compared to the rest of population. Not only do we really enjoy what we do but we also get to choose what to work on ourselves. Sure, there is the dark world of academic bureaucracy and the perpetual fight for grant money but I still think that we are an extremely lucky bunch. I am not aware of any other profession where the situation is similar.

Now and then, we forget how truly exceptional our situation is and take this privilege too much for granted. Then, we try to forget about the outside world and, hidden in our ivory towers, fight against every change in the academic environment. Some times, we feel offended by accusations of sexism. Other times, we find it outrageous that we should move science to social media and to the public.

I am sure there are bad scientists who vent their frustrations by criticising the works of others on the internet. But there is also a large group of researchers who do not forget about the world outside the academic milieu and want to share the amazing science they do with others — it can be fellow researchers who do not work in exactly the same field of study, family and friends who never stop asking about one’s work, or anyone willing to listen. We then start our blogs where we talk about our own research, the work done by our fellow scientists, our approaches to tackling problems we face at work, and the joy our daily lives bring.

Maybe we will not publish as many papers as those who do not see beyond their ivory towers because we are not so focused on our research output. But there are many ways in which scientists can contribute to the community; publishing own results, reviewing works done by others, mentoring and teaching younger generations, or sharing our passion for science with the rest of the world are just a few. It is, of course, impossible to judge who is the best scientist but, as long as we all contribute in a positive way, that does not (or should not) play a role. At the end of the day, science is not a solitary endeavour but a benefit to the society.

We also must not forget that it is the public who lets us work on problems we find fascinating. The least we can do in return is tell them what we did and how it will benefit them; otherwise, we might wake up one day and find them not willing to finance our work any more. Sure, it is not always immediately clear why our results are so important or how they can be applied to benefit mankind but hiding our work from the lay public is not a solution. Even such abstract fields as theoretical mathematics can be made accessible to those willing to learn something new.

Long-term commitment to disseminate research to the public is not an easy one. But without it, it is difficult to get society to trust science and we cannot expect the public to listen to us when presenting important findings. For instance, if we want to convince public that climate change is a real threat to our civilisation, we have to explain how we found that out and what the findings mean for our near future. If we ask the public to trust us blindly, all we can expect is skepticism and denial.

I am not implying that every scientist has to blog. As I said above, there are many ways in which researchers can contribute to the community, and blogging is just one of them. If someone finds it difficult or thinks they can contribute better in other ways, that is perfectly fine. But damning every science blogger and claiming they are all failures is a very short-sighted approach.