The twin paradox states the following:

There are two identical twins. One of them travels through space in a high-speed rocket. When they return home, the Earth-bound twin has aged more. This is a result of special relativity. Very briefly, this is due to time slowing down as higher speeds are reached, and why Matthew McConaughey returned to Earth only to find his 90-something year old daughter on her dying bed.

This thought experiment has long been exactly that, a though experiment. But recently, we actually were able to learn what happens to twins when one is in space (granted, not in a high-speed rocket, but on the ISS) for almost a year, while the other twin stays on Earth.

Real Space Twinsies

On March 27 2015, astronaut Scott Kelly arrived at the International Space Station (ISS), while his brother, astronaut Mark Kelly, remained on Earth. (One can have a discussion on who was the luckier of the two.) They did the same activities, ate the same things, and followed the same schedule*, the only difference being that Scott was 400 km from the Earth’s surface, travelling at a speed of 7.66 km/s, while Mark was 0 km from the Earth surface, travelling at a speed of merely 460 m/second, as we all are.

340 days later, March 1 2016, Scott returned to Earth. For the full duration of his time on the ISS, as well as after his return, numerous samples were collected and tests were conducted to monitor his health and compare the physiological and biological changes that happened as a consequence of spacelife. Using his twin brother, a perfect genetic duplicate, as a control.

twins patch
The Twin Study, a massive undertaking involving lots of collaboration and fancy badge design.

The effects of space

There are many “unusual” aspects about living in space, compared to living on Earth, including the odd noises of the ISS, the isolation (Scott was in contact with a mere 12 people during those 340 days), the ultra-controlled environment, a disruption of the normal body clock (imagine perpetually being jet-lagged because of constant switching of time zones), living in micro gravity and the excess of radiation.

An ultra-combined effort, i.e. a major collaboration between a lot of different labs that looked at all possible aspects of physiological and biological function, the effects of 340 days in space (in this specific set of twins) was published last month. There are a lot of changes that occur to the human body in space, some more severe than others.

An immense effort and a lot of numbers went into creating, collecting and comparing samples from the twins. Credit: NASA

There are some changes that don’t really matter much, like changes in the gastrointestinal microbiome and changes in biomass, which were affected during Scott’s time in space, but rapidly returned to normal after he returned. Not much to worry about.

Mid-level risks included known effects of living in microgravity such changes in bone density (you don’t really need to use your skeletal muscles while floating around) and changes in how the heart pumps around blood (you don’t need to fight gravity to pump blood to the head). NASA already knows this and therefore has a rigorous rehabilitation program for returning astronauts to re-acclimatize to Earth’s gravity.

However, it’s the high-risk findings that we all have to worry about, which a mostly due to prolonged floating and prolonged radiation exposure. Due to changes in air pressure as well as that thing I mentioned about blood pumping, a lot of astronauts experience ocular issues after their return, a risk that only increases with increased dwell time off-Earth. This can severely compromise vision. There is also evidence of some cognitive decline. Both those aspects are worrying in the light of long term space travel, we would hope that space-explorers can see and think clearly while carrying out dangerous tasks in dangerous conditions. And that’s without considering a final severe risk…

Who’s the oldest twin?

In addition, the radiation that Scott experienced on ISS is pretty much equivalent to 50 years of normal exposure on Earth. This causes significant genomic instability and DNA damage, and consequentially an increased risk of developing cancer.

One example of this genomic instability has to do with telomeres**. Telomeres are bits of DNA that cap the end of chromosomes. Every time a cell divides, and in the process duplicates its whole DNA library, the telomeres get shorter. When they get too short, the cell can no longer divide. This is something that happens naturally during aging: shortening of telomeres phases out cells until they can no longer divide. Eventually, this leads to cell death.

1 year of space had an odd effect on Scott’s telomeres. Some of them grew longer, while others showed shortening. However, the lengthened telomere returned to normal after Scott’s landing on Earth, while the shortening persisted. So even though Scott was the space twin in our paradox, he seems to have ended up aging faster than Mark…

At a glance, the different effects of one year in space on a human body. Well, it probably takes more than a glance to read this.

A lot happens to a body in space

Overall, the results are pretty surprising, prolonged living in space had more of an effect on the human body than researchers expected. And there is probably a lot more to learn, even just with the data collected from Scott and Mark.

On one hand, the twin study showed how resilient and robust the human body is. 91.3% of Scott’s gene expression levels returned to his baseline level within six months of landing, and some of the changes that occurred to his DNA and microbiome were no different than what occurs in high-stress situations on Earth. That’s amazing, the human body has not evolved to survive in space, but it seems to do pretty well considering how outlandish the conditions are!

On the other hand, the prolonged exposure to microgravity and high radiation does have severe effects on the human health, leading to increased risk for compromised vision, cardiovascular disease, and cancer development. Even with the rigorous preparation and rehabilitation programs astronauts go through before and after spaceflight, some of these effects will be impossible to avoid.

The massive study, combining the effort of 84 researchers in 12 different universities is a feat of collaboration (though nothing compared to the black hole telescope, if I’m honest) and it’s definitely a first that the genomes of space vs. Earth could be compared with a true genetic control. This compiled study, and the many pieces of research that are expected to be published in the next year with the results from the individual studies, provide crucial insight on the effects of space in the long term. If we think that it takes approximately 1 year for a return journey to Mars, this research is valuable for the health of future astronauts and mankind’s ambition to explore further into space.

Want to know more? Watch NASA’s video on the three key findings, or read more in the Science paper or the NASA website (links below).


Markus Löbrich and Penny A. Jeggo. Hazards of human spaceflight. Science 364 (6436) p. 127-128. 2019. DOI: 10.1126/science.aaw7086

Francine E. Garrett-Bakelman, et al. The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight.
Science 364 (6436) eaau8650. 2019. DOI: 10.1126/science.aau8650

Twin study on the NASA website:

Cover image: The International Space Station crosses the terminator above the Gulf of Guinea, image credit NASA

*I remember reading this somewhere, but I cannot find the source anymore. It is thus possible that Mark just went about his normal life. Regardless, it is amazing that NASA had the opportunity to do this experiment with a perfect genetic control.

** Fun fact, my spelling check does not know the word “telomeres” and suggests that I mean “omelettes”. Well, I guess they both get super scrambled up in space? (Eeeeh for an inaccurate joke, sorry).


Earth Day Special

Happy Earth Day! To celebrate our amazing world, here are some amazing views of our blue planet from outer space:

The first photograph of our Earth from space was taken in 1946. Unfortunately, the beaut could not fit in the whole field of view!
(Image credit: White Sands Missile Range / Applied Physics Laboratory)
With some stitching magic, the first pictures of Earth from an altitude greater than 100 miles were published in 1947.
(Image credit: Johns Hopkins Applied Physics Laboratory)
The first full color view of our planet was taken by the ATS-3 satellite in 1967. This could have been prompted by Stewart Brand‘s campaign to have NASA release an image of the entire earth from space. He sold buttons (¢ 25) with the words: “Why haven’t we seen a photograph of the whole Earth yet?” and used the image above as a cover for his Whole Earth Catalog.
(Image credit: ATS-3 / NASA)
Earthrise, as seen from the moon.
I’m running out of words here, just enjoy the views!
(Image credit: Apollo 8 / NASA)
The Blue Marble, 1972. Taken from about 29,000 km (18,000 miles) from the surface by the Apollo 17 crew on its way to the moon.
(Image credit: Apollo 17 / NASA)
A final picture from 1990 to make you feel small. We are that Pale Blue Dot seen in the right band of sunlight reflected by the camera. The Voyager 1 space probe captured this image at a distance of about 6 billion km (3.7 billion miles) from earth.

Inspired by a talk by Dr. Oliver Fraser I attended at the Theodor Jacobsen Observatory (University of Washington)

Cover image: Apollo 10 / NASA

One printed heart, please

It goes without saying that 3D printing is cool*. The ability to think up any three dimensional structure, design it in a 3D design software and have it materialize blows my mind. Granted, I’m making it sound like it’s a very easy and fast process and I know that’s often not the case, but I also know that for a lot of engineering and physics laboratories, the ability to relatively quickly print a model or prototype for anything is extremely useful. In addition, it’s an amazing educational resource. You can print model organs, molecular structures, planets, … and have something physical to show or throw around during a science demo.

Just to name a few reasons why 3D printing is cool.

What is possible even cooler is the potential of printing tissues and organs. And now, for the first time according to a group of researchers in Tel Aviv, it has happened: a complete 3D heart was printed.

They started with some cells isolated from a sheet of fatty tissue from a human patient. These cells were reprogrammed to what’s called pluripotent stem cells. Pluripotent stem cells have the potential to give rise to many different cell types , depending on the biochemical cues they get – for example by changing the formulation of the culture media, which contains nutrients, hormones and other components to “feed” the cells.

In this case, the cells were driven towards being heart muscle cells and blood vessel cells. By mixing these cells with a personalized hydrogel, consisting of collagen (remember, from the reindeer eyes?) and glycoproteins (proteins have a sugar molecule connected to it), the researchers created a “bioink”, a material that could be used to print cardiac tissue in the same way a 3D printer prints 3D structures using a plastic “ink”.

3D printing a mini-heart (image credit AFP or licensors)

While the 3D printed heart – currently around the size of a rabbit’s heart – cannot beat yet, the possibility to be able to print custom organs, starting from a patient’s own cells and therefore eliminating an immune response, is of major importance for medical applications. To enable heart function, the heart cells would have to be taught how to contract in an organized manner, and create a beating heart.

Beating has already been achieved in heart organoids. Organoids are little mini-organs grown in a petri dish, that mimic the organization and function of an organ in a living organism. The difference between 3D printed organs and organoids, is that organoids are allowed to form their own structure and cell types, driven by the media cocktail they are given, while 3D printing positions already differentiated cells in a 3D scaffold. Heart organoids, starting from one or a few reprogrammed cells, grow into structured groups of cells that spontaneously start beating.

Beating heart organoids (gif from Popular Mechanics US)

These organoids, however, don’t really mimic the structure of the heart unless you “force” structure by growing these mini-hearts in a mold, basically geometrically confining the cells to form a predefined structure.

A model of a pumping heart was developed last year, creating an in vitro biomimetic system that could help with drug discovery and studying cardiac diseases. While it doesn’t look as much as a heart as the 3D printed one developed by the Israeli research group, it’s still pretty amazing to watch this little blob of tissue beating under electrical stimulation:

In any case, I hope to see a combined version of all of the above: a 3D printed, functional heart. Nevertheless, this first (though debatable if they actually were the first) 3D printed heart is pretty awesome and has a lot of potential applications in medicine and clinical research. Not to mention that it looks pretty cool:

3D confocal image of the printed heart (Advanced Science, scale bar = 1mm)

Sources used:

Noor N., Shapira A., Edri R., Gal I., Wertheim L., Dvir T. 3D Printing of Personalized Thick and Perfusable Cardiac Patches and HeartsAdv. Sci. (2019), 1900344.

Ma Z., Wang J., Loskill P., Heubsch N., Koo S., Svedlund F.L., Marks N.C., Hua E.W., Grigoropoulos C.P., Conklin B.R., Healy K.E. Self-organizing human cardiac microchambers mediated by geometric confinement. Nat. Comm. 6 (2015), 7413.

Li R.A., Keung A., Cashman T.J., Backeris P.C., Johnson B.V., Bardot E.S., Wong
A.O.T., Chan P.K.W., Chan C.W.Y, Costa K.D. Bioengineering an electro-mechanically functional miniature ventricular heart chamber from human pluripotent stem cells. Biomaterials 163 (2018), 116-127.

*Sudden realization that most (if not all) of this blog is me saying “Hey, did you hear about this science thing, it’s really cool!!”

Supermassive black hole

Step one – press play on this video:

Step two – stare into this picture for the full 3-and-a-half minutes (that’s the length of the song, you’re free to stare for longer):


Credit: Event Horizon Telescope Collaboration

Step three – find out more

Oh hey, scientists have taken the first ever picture of a black hole. This is amazing.

Note: I intend to write another blog post this week, I just wanted to share this black hole news!

Forget diamonds, liquid crystals are a girl’s best friend!

A few months ago I lost my mood ring. Which is very discerning; I haven’t been able to tell what my mood is since then!

I was reminded of my lack of mood-reading device in Vancouver last weekend. I was in one of those fantasy-merch shops that sells lots of dragon statues. I was admiring their collection of mood rings and wondering whether I should buy a new, when I suddenly realized I didn’t actually know how mood rings work.

My friend and I used to have full conversations consisting of pictures of our mood rings. “It’s really cold out” was a picture of a black or brown ring.

To the google!

Thermochromic materials

Mood rings don’t actually tell what your mood is (sorry). They do give some indication of your skin temperature, which I guess is slightly related to your mood but probably more related to the weather and how cold you’refeeling. Created in 1975 by New Yorkers Josh Reynolds and Maris Ambats, mood rings were a fad in the 1970s, and probably again in the 1990s if I remember correctly. To be honest, they’ve never really left the mystic thingumabob shops, or souvenir shops (as you might be able to tell by the Celtic knot design in the picture above; I bought the rings for my friend and me in a Scottish souvenir shop).

The change-changing part of a mood ring is a thermochromic material, i.e. a material that changes color (chroma -χρῶμα) due to a change in temperature (thermosθερμός).*

There are different examples of thermochromic materials and a number of different applications. Those t-shirts that change in color if you press your hand on them. Those cups that change color when containing a hot liquid. Those little thermometer rulers that change color if you hold them in your hand. And mood rings.

Liquid crystals

The type of material in a mood ring, that changes color according to changing temperature, is a liquid crystal.

If you had some intro to chemistry at some point, you might remember hearing that crystals have a very organized structure, with atoms (or molecules) forming a lattice. Perhaps you did an experiment where you made salt crystals by evaporating water from salt water in a dish. But you probably remember that crystals were not liquid.

Then what are liquid crystals? Basically, it’s a state of matter which lies in between liquids and crystals. Usually, liquid crystal molecules are elongated, so depending on their packing they have more crystal-like properties (dense packing) or more liquid properties (looser packing). Depending on their “phase”, i.e. structural organisation and packing, the optical properties of liquid crystals change.

Liquid crystals consist of elongated moleduces that change their optical properties depending on their organization. Image from:

The molecules in a liquid crystal can take up different degrees of order:

  1. No order; basically the material is a liquid with properties of a fluid. (A in the very professional sketch below.)
  2. Some order; the molecules sort of align in the same direction, but not along a plane (B).
  3. More order; the molecules start organizing themselves along planes (C).
  4. Full order; all molecules are neatly arranged in a regular lattice structure. Wait, this is a full crystal! (D)
I’m getting into the habit of creating illustrations on origami paper.**

As stated, with changing orientation and order, the optical properties change, similar to the collagen from a previous post. Depending on how organized the molecules are, different light wavelengths are reflected by the mood rind “gem”. In other words: the warmer the mood ring gem gets, the less organized the liquid crystal molecules are, and that causes a shift in color.

So if you’re feeling unsure about your mood, mood rings don’t actually help, but I’ve found that they are quite a conversation starter. But now, instead of handing your ring to whomever exclaims “Oh cool! A mood ring! Can I try it on?“, you can also explain exactly how it (doesn’t) work.

I just bought myself a new one. ***

Cover image credit: Kaszynski lab

* Using any excuse to use the Greek alphabet for something other than fraternity names. I now walk to work through Fraternity Lane (not the actual name), so I’m constantly reminded of the letter φ.

** Bonus pic – origami flowers from those same pieces of paper:

*** Bonus pic 2 – New ring!


A few weeks ago, I went to a public lecture – attractively named “Wine Down with Science” – organized by UW Medicine and I’ve been trying to tell people about it ever since.

The first problem is that the topic of the talk is one of those words that I’ll always just struggle to pronounce on the first go:


I went to the event not knowing what it was going to be about. I was already sold when I read it was a public lecture about some ground breaking research; any excuse to listen to science in a more informal setting. Turned out, it was good of me to go, because it was sort of about biophysics and biophysics is sort of my jam.

So what is the *insert long word here again*?

Proprioception you mean? According to the event announcement, the lecture title was: Out of Your Mind: The Inner Workings of Your Mysterious Sixth Sense. So proprioception is about seeing dead people?

Sorry to break it to you kid, but that’s not really a thing.

Nope. In reality, proprioception is our ability to be aware the position and movement of our body and its parts. Not having proprioceptive abilities is one of the reasons that man-mimicking robots fail at a lot of seemingly basic tasks. They have no internal feedback system to tell them how their parts are positioned or moving with respect to each other, making benign tasks hard to do.

I feel bad for laughing but it is very funny.

With proprioception, we know exactly how are body is positioned: whether our arms are bent, our feet are flexed, our eyelids are closed (okay, there are other ways to tell). And that without having to look those body parts. There are some known cases of people losing their sense of proprioception and it causes paralysis (if you have 10 minutes to spare, you should really check out this video about a man who lost his sense of proprioception but taught himself to walk using visual cues instead).

How can we study this proprioception thing?

This is where it gets even cooler. The lecturer – John Tuthill – explained how in his lab, they use a clever combination of lasers, genetic tools, virtual reality, and fruit-fly-treadmills to understand how proprioception works.

Fruit fly on a floating ball tread mill. I can look at this for hours. From:

By making a fruit fly run on a floating ball, and surrounding it with screens, they can trick the fly into thinking it’s strolling somewhere outside and track the neuron activity during movement. Using a laser, they can turn off the proprioceptive neurons very locally (using something called optogenetics, but that’s for some other time). For example, if by blocking proprioception in one of the fly’s legs, i.e. stopping communication between the leg and the central nervous system, they temporarily paralyze that leg. After turning the laser back off, the fly trods on as if nothing has happened.

Why should I worry, why should I care?

(Any excuse to play that song).

First of all, part of science is just understanding how things work. Knowledge for knowledge’s sake. But there are also some useful applications of this knowledge, such as helping people with movement disorders. And helping robot-designers to not make robots that seemingly stupidly fall over.

On the other hand, we can make robots do Walking manalready. Source: Boston Dynamics

This talk was by John Tuthill, PhD, Assistant Professor of Physiology and Biophysics. His work is really cool. Go check it out.

Behind blue eyes

Occasionally, a colleague passes by my desk and says something along the lines of “Hey, did you know that *insert fun – usually science-related – fact here*?”

The other day, this exact thing happened:

“Hey, did you know that reindeer’s eyes turn blue in the winter?”

The question was prompted by the magnificent drawing of an octomoose (name pending) on the white board in our office. How the octomoose came about, is not that interesting a story, but I would want to share with you that we held a poll to determine the name of the 8-tentacled creature. My vote was for moctopus. I did not win (6 vs 3 votes).

Behold the mighty octomoose. Name votes currently stand at 3 for “moctopus”, 6 for “octomoose”.

So now that winter has come to an end, let’s talk about those weird reindeer eyes.

Discerningly, the first suggestions google search gave me when I typed in “reindeer eyes” was “reindeer eyes recipes”, which is just creepy; though actually clicking through reassured me that it was about chocolates and cookies (phew).

The struggle did not end there. The next page I found had a photo of a “summer reindeer eye” vs a “winter reindeer eye”:

Credit: Alexandre Buisse. From this website.

Jackpot? Nope. The photo was photoshopped (quite obviously). Sigh. This is turning out to be a lesson in fact checking.

In the original, the reindeer has brown eyes. Never trust photos you find on the internet, I guess .

However, I was not chasing a myth. It’s still true that reindeer’s eyes change color from gold in the summer to blue in the winter. Proof of this is in a scientific paper (hurray for backtracking to the source) which features some very creepy photos of reindeer eyeballs:

Reindeer eyes collected from reindeer killed in the winter (left) and in the summer (right). Credit: Glen Jeffery

The explanation to why this happens seems to lie in the reflective layer that sits behind the retina: the Tapetum lucidum. A lot of mammals have this layer; you might have noticed it when shining a light in your cat’s eyes (and survived to tell the tale). This extra layer helps animals see when it’s all twilight-y. It reflects light that passes through the retina, causing the light to pass through the retina twice, giving the light-detecting cells of the retina a second chance to detect any photos. When you see that yellow glow in your cat’s eyes, it’s the light reflecting right back at you off their Tapetum lucidum.

The Tapetum lucidum sits right behind the retina and causes creepy glowy yellow eyes in most mammels. Image from

The next bit of eye knowledge you need to understand the changing reindeer eye color is the fact that pupils widen and shrink depending on how much light is available. Dilated pupils allow more light to enter the eye, and hence more photons can be detected by the light-sensing cells in the retina.

Dilated pupils, a sign of darkness. Or physical attraction. Or drug use. But for the sake of this post it’s a sign on darkness; let’s just go with that.

In the arctic winter – basically 3 months of darkness – the reindeer’s pupils are continuously dilated. The constant effort to keep the irises open, constricts the small vessels that usually drain fluid out of the eyes. This in turn causes a pressure buildup within the eye, which compresses the Tapetum lucidum.

The Tapetum lucidum is mostly made up of a protein called collagen. This fibrous protein is a hydrogel, an ordered mesh of fibers that absorb and retain fluid. However, when this mesh is compressed, the fluid is squeezed out (like when you squeeze a sponge) and the orderly rows of collagen fibers become more tightly packed. The type of light that is reflected by the Tapetum depends on the spacing between these fibers. When they are “normally” spaced, like in the summer, longer wavelength light (yellow) is reflected, giving the Tapetum a golden color. When tighter packed, blue wavelengths (which are shorter) are reflected, giving the reindeer blue eyes.

In short, in the months of darkness, reindeer’s pupils are permanently dilated, leading to swollen eye, leading to compression of the collagen fibers, changing the color that is reflected by the Tapetum.

Or, in a drawing, if you will.

Research is still ongoing, because even though the mechanism behind eye-color-change has been explained, the effect on eye function is still unclear. Perhaps this change in eye color changes the sensitivity of the eyes. And why do other arctic animals, who also live through months of perpetual darkness, not have this cool change in eye color?

However, one thing is for sure, Rudolph’s red nose cannot be explained by science. Yet.

And in the mean time, octomoose remains on our office white board.