28 April 2018

How to read a scientific paper 4.0

This artist’s impression shows how the Milky Way galaxy would look seen from almost edge on and from a very different perspective than we get from the Earth. The central bulge shows up as a peanut shaped glowing ball of stars and the spiral arms and their associated dust clouds form a narrow band.
And now the last step in reading the paper, reading the whole paper. I chose an article Discovery of Gamma-Ray Emission from the X shaped Buldge of the Milky Way. You can find a full article for free at arxiv.org. And if you feeling posh, you can also buy the version that was published in Nature.
Here is a ‘triage’ average grad student uses when reading scientific papers, and I follow that ‘triage’ here. Links will lead you to the posts that covered previous steps.

And now let us do the final step.

Read the paper in details

At the beginning of each paper, something like an introduction is given. The purpose of this section is to place this particular results in the context of the previous knowledge. There you can find what connects this particular paper with the previous knowledge and also you can determine why did scientists bother with all this in the first place.

First paragraph — Introduction

An opening paragraph tells us exactly why this research is done and why is important. One of the telescopes, Fermi Gamma-Ray Large Area Telescope detected the signal with the spectral peak at ~2 GeV. The catch is that this particular signal with its characteristic matches the theoretical assumption on how self-annihilation of dark matter particles should look like. Basically offering firm evidence of the existence of the dark matter. Something astrophysicists are trying to find for decades now.
In astronomy, observational and theoretical branch work in concert. To fully understand why are we observing something in the sky, we also try to simulate the event using our current knowledge of physics. Sometimes, we observe something we do not have an explanation for, sometimes we make theories that cannot be observed (i.e. string theory).
In the research predating this paper, three scientists, Navarro, Frenk, and White devised simulation of self-annihilation of the dark matter particles, which gave info about how to detect such process. And it seemed like this telescope did.
The catch was that a similar signal could be produced by a different process, like pulsars. And in the last sentence of the first paragraph authors state that there was another study or two who might indicate that observed signal is not made by dark matter.

Second paragraph —more introduction

And here we have a quite important explanation of why is this signal easily confused between the two possible options. The scientists here did not observe the clear strong signal. Nope, they are observing and analyzing tiny variation in the overall strong and overwhelming main signal. It is similar to trying to detect the variation in your voice caused by your heartbeat. There is some. It is very tiny, and to see it, you first have to remove almost all voice away, leaving only the tiny sound made by your heart.
In this paragraph, scientists explain that is exactly what they need to do, they need to model somehow the big signal adding in it all known sources of gamma radiation in that particular part of the sky. And they have to be careful how to do so, because, if they do not model perfectly each and every of known sources, they will not be able to remove them from the detected signal and they will never be able to see real leftovers.
So in this paragraph, the known sources are listed, and everything that makes modeling hard is stated.
From those two paragraphs, I can also conclude that this particular paper is one of the negative results ones. Scientists wanted to find dark matter. They analyzed the signal and found none. In essence, the signal they hoped is a dark matter turned to be just, spoiler alert, a bunch of pulsars. Finding evidence of a dark matter is almost as a holy grail for astrophysics. The person who does it will enter history.
The negative-results papers are crucial for science. They are what keeps science honest. The existence of such papers also demonstrates that for the scientific community, the truth is more important than fame and ego stroking.

Third paragraph — Methods

This paragraph serves as a presentation of their main tool, their own novel analysis that allowed them to confidently remove all known sources of gamma rays, leaving only that signal that might be a dark matter signal.
You will note that in this paragraph scientists keep mentioning that details are in an appendix. See, this particular section of the paper is the most important one in deciding is the paper worth of attention or not. The basis of the scientific method is that all techniques, models, and research paths have to be reproducible. The whole point is to eliminate the ‘because I say so’ point of view of one human individual. We are notoriously bad witnesses and tend to color our observation with the current biases and emotions. The scientific method is constructed to eliminate this innate human bias and get to the truth. Therefore, every good scientific paper will explain their research methods in enough detail that anyone who is willing to try can repeat the experiment. Yes, even you. Granted, you would have to learn loads of physics and background mentioned in each and every cited paper in the reference section, before you could even attempt to do an experiment. But if you’re willing to learn, you can.
This paper is not an exception. They present the necessary details (in the appendix), the details to other scientists to scrutinize and check. Because paper is scientific only if all the details are actually doable steps, and the whole procedure cannot be reduced to that recipe of Underwear Gnomes from South Park. You know,
  1.  Underwear
  2.  ?
  3. Profit
The true scientific method does not have question mark steps. This also explains why scientists will outright reject the so-called ‘scientific papers’ from pseudo-science. Those follow the recipe of Underwear Gnomes and have lots of question marks steps in their techniques.
to be continued...

No comments:

Post a Comment