Saturday, 21 January 2017

Proton: a life story

Proton: a life story 
by Geraint F. Lewis


1035 years: I’ve lived a long and eventful life, but I know that death is almost upon me. Around me, my kind are slowly melting into the darkness that is now the universe, and my time will eventually come.

I’ve lived a long and eventful life…


10-43 seconds: A time of unbelievable light, unbelievable heat! I don’t remember the time before I was born, but I was there, disembodied, ethereal, part of the swirling, roaring fires of the universe coming in to being.

But the universe cooled. From the featureless inferno, its character crystalized into a seething sea of particles and forces. Electrons and quarks tore about, smashing and crashing into photons and neutrinos. The universe continued to cool.

1 second: The intensity of the heat steadily died away, and I was born. In truth, there was no precise moment of my birth, but as the universe cooled my innards, free quarks, bound together, and I was suddenly there! A proton!

But my existence seemed fleeting, and in this still crowded and superheated universe in an instant I was bumped and I transformed, changing from proton to neutron. And with another thump I was a proton again. Then neutron. Then proton. I can’t remember how many times I flipped and flopped from one to the other. But as the universe continued to cool, my identity eventually settled. I was a proton, and staying that way. At least for now!

10 seconds: The universe was now filled with jostling protons and neutrons. We crashed and collided, but I was drawn to the neutrons, and they to me. As one approached, we reached out to one another, but in the fleeting moment of a touch, the still immense heat of the universe tore us apart.

The universe cooled, and the jostling diminished. I held onto a passing neutron and we danced. Together we were something new, together we were a nucleus of deuterium. Around us, all of the neutrons found proton partners, although there were not enough to go around and many protons remained alone.

1 minute: And still the universe cooled. Things steadily slowed, and before I realised we had grabbed onto another pair, one more proton, one more neutron, and as the new group we were helium. And it was not just us! All around us in the universe, protons and neutrons were getting together. The first elements were being forged.

But as quickly as it begun, it was over. The temperature continued to drop as the universe expanded. Collisions calmed. Instead of eagerly joining together, us newly formed nuclei of atoms now avoided one another. I settled down into my life as helium.

380,000 years: After its superbly energetic start, the universe rapidly darkened. And in the darkness, other nuclei bounced around me. Electrons, still holding on to the fire of their birth, zipped between us. But the universe cooled and cooled, slowly robbing these speedy electrons of their energy, and they were inexorably drawn closer.

Two electrons joined, orbiting about us protons and neutrons. We had become a new thing entirely, an atom of helium! Other helium nuclei were doing the same, while lone protons, also grabbing at electrons, transformed into hydrogen! This excitement was fleeting, and very soon us atoms settled back into the darkness.

10 million years: The universe was still dark, but that didn’t mean that nothing was happening. Gravity was there, pulling on us atoms of hydrogen and helium, pooling us into clouds and clumps. It felt uncomfortable to be close to so many other atoms, and the constant bumping and grinding ripped off our electrons. Back to being just a nucleus of helium!

Throughout the universe, many massive lumps of hydrogen and helium were forming, with intense gravity squeezing hard at their very hearts. Temperatures soared, and protons again began to crash together, combining first into deuterium and then into helium, and then into carbon, oxygen and other elements not yet seen in the universe. And from these furnaces came heat and light, and the first stars shone and lit up the darkness.

2 billion years: I was spared the intensity at the stellar core, riding the plasma currents in the outer parts of a star. There was a lot of jostling and bumping, but it was relatively cool here, and I retained my identity of helium. But things were changing.

My star was aging quickly, and instead of the steady burning of its youth, it began to groan and wheeze, puffing and swelling as its nuclear reactor faltered and failed.  The stellar pulsing was becoming a wild ride, until eventually I was blown completely off the star and thrown back into the gas of interstellar space.

3 billion years: I swirled around for a while, bathed in the light of a hundred billion stars. But gravity does not sleep and I soon found myself back inside a newly born star. But this time it was different! No sedate atmospheric bobbing for me. I found myself in the intense blaze of the stellar core.

The temperature rose quickly, and nuclei smashed together. These collisions were violent, with a violence I had last seen at the start of the universe. And after a bruising series of collisions, I was helium no more. Now I resided with other protons and neutrons in a nucleus of carbon.

3.1 billion years: The stellar heart roared, and just beneath me the fires burnt unbelievably hot. Down there, at the very centre, carbon was forged into oxygen, neon and silicon, building heavier and heavier elements. Eventually the stellar furnace was producing iron, a nuclear dead-end that cannot fuel the burning that keeps a star alive.

As the fires at the stellar furnace continued to rage, more and more iron built up in the core. Until there was so much that the nuclear fires went out and the heart of the star suddenly stopped. With nothing to prevent gravity’s insatiable attraction, the star’s outer layers collapsed, and in an instant this crushing reignited the nuclear fires, now burning uncontrollably. The star exploded and ripped itself apart. In my new carbon identity, I found myself thrust again out into the universe.

5 billion years: Deep space is now different. Yes, there is plenty of hydrogen and helium out here, but there are lots of heavier atoms, like myself, bobbing about, the ashes from billions of dead and dying stars. We gather into immense clouds of gas and dust, illuminated by continuing generations of stars that shine.

In this cool environment, we can again collect some electrons and live as an atom, but this time an atom of carbon. Before long, we’re bumping into other atoms, linking together and forming long molecules, alcohols, formaldehydes and more. But gravity is at work again, tugging on the clouds and drawing us in. It looks like I’m heading for another journey inside a star.

8 billion years: Although this time it’s different. I find myself in the swish and swirl of material orbiting the forming star. And strange things are happening, as molecules build and intertwine, growing and clumping as the fetal star steadily grows. The heart of the star ignites, and the rush of radiation blows away the swirling disk, sending back into deep space.

But I remain, deep in a molecule bound with other molecules and held within a rock, a rock too large to billow in the solar wind. And these rocks are colliding and sticking, growing and forming a planet. In the blink of a cosmic eye, billions of tonnes have come together, which gravity has moulded into a ball. Initially hot from its birth, this newly built planet steadily cooled and solidified in the light of its host star.

10 billion years: For a brief while, this planet was dead and sterile, but water began to flow on its surface and an atmosphere wrapped and warmed it. I remained in the ground, although the rocks and the dirt continued to churn as the planet continued to cooled.

And then something amazing happed! Things moved on the surface! I didn’t see how it began, but collections of molecules were acting in unison. These bags of chemical processes slurped across the planet for billions of years, and then themselves begun to join and work together.

13 billion years: Eventually I found myself caught up in this stuff called life, with me, as carbon, integrated into the various pieces of changing and evolving creatures. But it was oh so transitory, being part of one bit of life, then back to the soil, and then part of another. Some times, as one type of life, other life consumed me, with molecules dismembered and reintegrated into other creatures.

Once I found myself in the fronds of a plant, a fern, waving gently in the breeze under a sunlit sky. But when this beautiful plant died, its body was pressed into the mud of the swamp in which it sat, and I was ripped evermore from the cycle of life. Pressures and temperatures grew as more and more material was pressed upon me, and I was buried deeper and deeper within the ground.

13.7 billion years: And there I lay, with the intense squeezing rapidly ripping away my molecular identity. Again, I was simply carbon. But here, deep in the planet, there were a lot of carbon atoms and slowly we found affinity for one another. Through soaring pressures, we bound together, pressed and shaped into a crystal, a crystal of diamond.

Suddenly I was torn from my underground home, gazed at by a living creature I had never seen before. Accompanied by some gold, I spent a mere moment of the cosmos adorning the finger of one of these living creatures, these humans. This was truly some of the strangest time of my existence, oh the world I saw, but before long I was lost and buried in the dark ground. And there I stayed as rocks shifted and moved, and the planet aged.

19 billion years: With many other carbon atoms, I was still locked in diamond as the planet started to melt around me. The star, whose birth I had witnessed, was now old. It glowed intensely, immense and swollen, so that its erratic atmosphere engulfed the planet. The heat and the raging wind of the dying star ripped at the planet’s surface, hurling it into space.

And so too I was gone, embedded in the dust of my long dead planet, thrown again into space between stars. The rocky core of the planet that had been my home for almost ten billion years continually dragged against the star’s immense atmosphere, and fell to complete annihilation in the last beats of the stellar heart.

100 billion years: All around me, the universe has continued to expand and cool, but the expansion, originally slowing, has been steadily accelerating. Immense groups of stars, the galaxies, are moving away from each other faster and faster. Their light, which blazed in the distant universe, has dimmed and diminished as they rushed away.

And by now the expansion is so rapid all of these distant galaxies have completely faded from view. Near me, stars continue to burn, but now set in the infinite blackness of a distant sky.

1 trillion years: The universe got older and my journey continued. Each time the story was the same; I’d swirl in space before gravity’s irresistible pull dragged me into a forming star. My diamond identity was rapidly lost on my first such plunge, with the immense pressures and temperatures ripping us into individual atoms of carbon. Eventually the star aged and died and I was spat back out into space.

While the story of stellar birth and stellar death repeated, I noticed that that there was steadily less and less hydrogen, and more and more other elements tumbling through interstellar space. And while I sometimes existed fleetingly in this molecule or that, I inevitably found myself pulled into flowing into the birth of a new star.

10 trillion years: I have passed through countless generations of stars, each time slightly different. Many of these have been relatively gentle affairs, but now and again I find myself caught up in a massive star, a star destined to explode when it dies.

And within this stellar forge, my identity was changed to heavier and heavier elements. But in the eventual cataclysm of stellar death, a supernova, the smashing of elements can create extraordinary heavy collections of protons and neutrons, nuclei of gold and lead. I emerged from one explosion in a nucleus of cobalt, 27 of us protons with 33 neutrons.

But this was not a happy nucleus, heaving and shaking. This instability cannot last. Relief came when one of many protons changed into a neutron, spitting out an electron and transforming us into nickel. But as nickel we did not settle, more heaves and shakes, and we continued to transform and transform again until we were iron, and then we are calm.

50 trillion years: The cycle continues, with endless eons in empty space punctuated with the burst of excitement spent within a star. But through each cycle, there is less and less gas was to be found in interstellar space, with many atoms locked up in the dead hearts of stars, dead hearts that simply sit in the darkness.  

And the stars are different too. Instead of the bright burning of immense young stars, the darkness is punctuated with an innumerable sea of feeble, small stars, lighting the universe with their faint, red glow.

85 trillion years: I am dragged once more into a forming star. While I don’t realise it, this is the end of the cycle for me as the puny star that is forming will never explode, will never shed its outer layers, never return me to the depths of deep space. More and more of my kin, the protons and neutrons, have an identical fate, a destiny to be locked seemingly forever in to the last generations of stars to shine. 

And deep within my final star, I am still hidden inside an iron nucleus. Around me, the nuclear furnace burns very slowly and very steadily, as some of the remaining hydrogen is burnt into helium, illuminating the universe with a watery glow.

100 trillion years: My star still gently shines, with many others scattered through the universe, but the raw fuel for the formation of stars, the gas between the stars, is gone. No more stars will ever be born.

The universe is a mix of the dead and the dying, the remnants of long dead stars, and the last of those still feebly burning, destined to join the graveyard when they exhaust the last of their nuclear fuel. From this point, only death and darkness face the universe.

110 trillion years: The inevitable has come, and my star has exhausted the last of its nuclear fuel. At its heart, the fires have gone out. My star has died, not with a bang, but with a very silent whimper.

And I, a single proton, am still locked inside my nucleus of iron, deep, deep within the star. It is still warm, a left over heat from when the fires burnt, and atoms bounce and jostle, but it’s a dying heat as the star cools, leaking its radiation into space.

120 trillion years: The last star, aged and exhausted, has died, and the universe is filled with little more than fading embers. The gentle glow continues for a short while, but darkness returns, a darkness not seen for more than a hundred trillion years.

The universe feels like it’s entering its end days, but in reality an infinite future stretches ahead. In the darkness, I still sit, locked within the corpse of my long dead star.

10 quadrillion years: The last heat in my star has gone, radiated away into space, and we are as cold and dark as space itself. Everything has slowed to a crawl as the universe continues to wind down.   

But in the darkness, monsters lurk. Black holes, the crushed cores of massive dead stars, have been slowly slurping matter and eating the stellar dead, and in the dark they continue to feed, continue to grow. My remnant home is lucky, avoiding this fate, but many dead stars are crushed out of existence within the black hole’s heart.

1031 years: Further countless eons have passed, eons where nothing happened, nothing changed. But now, in the darkness, something new is stirring, a slow, methodic activity as matter itself has started to melt. My kindred protons, protons that have existed since the birth of time, are vanishing from existence, decaying to be replaced with other small particles.

My own remnant star is slowly falling apart, as individual atoms decay and break down. My own iron home is also disintegrating around me, with protons steadily decaying away. All of the dead stars are steadily turning to dust.

1034 years:  The stars are gone, and I find myself alone, a single proton sitting in the blackness of space. In the darkness around me, protons are still decaying away, still ceasing to be. The universe is slowly becoming a featureless sea, with little more than electrons and photons in the darkness.

Looking back over the immense history of the universe, it is difficult to remember the brief glory days, the days where the stars shone, with planets, and at least some life. But that has all gone, and is gone forever.

1035 years: There are very few of us protons left, and I am amongst the last. I know the inevitable will come soon, and I too will cease to exist, and will return to the ephemeral state that existed before my birth.

I will be gone, but there are still things hidden in the darkness. Even the black holes eventually die, spitting decaying particles into the void. And after 10100 years, even this will end as the last black hole dies away. And as it does so, the universe will enter into the last night, a night that will truly last forever.
  


I’ve lived a long and eventful life…



Wednesday, 28 December 2016

Blog rebirth - a plan for 2017

It is now the twilight zone between Christmas and New Year. 2016 has been a difficult and busy year, and my recreational physics and blogging has suffered. But it is time for a rebirth and I plan to get back to the writing about science and space here. But here's some things from 2016.

A Fortunate Universe: Life in a finely tuned cosmos was published. This has sucked up a huge amount of time and mental activity, and that continues. I will blog about the entire writing and publishing process at some point in the future, but it really is quite a complex process with many mine-fields to navigate. But it is done, and am planning to write more in the future.
We also made a video to advertise the book!

I've done a lot of writing in other places, including Cosmos magazine on "A universe made for me? Physics, fine-tuning and life", and commentary in New Scientist and several articles in The Conversation including

Peering into the future: does science require predictions?

and

The cosmic crime-scene hunt for clues on how galaxies are formed

And one of my articles from last year, We are lucky to live in a universe made for us was selected for inclusion in The Best Australian Science Writing 2016,
There has been a whole bunch of science papers as well, but I will write about those when the blog is up and running at full speed :)

Saturday, 13 August 2016

For the love of Spherical Harmonics

I hate starting every blog post with an apology as I have been busy, but I have. But I have. Teaching Electromagnetism to our first year class, computational physics using MatLab, and six smart talented students to wrangle, takes up a lot of time.

But I continue to try and learn a new thing every day! And so here's a short summary of what I've been doing recently.

There's no secret I love maths. I'm not skilled enough to be a mathematician, but I am an avid user. One of the things I love about maths is its shock value. What, I hear you say, shock? Yes, shock.

I remember when I discovered that trigonometric functions can be written as infinite series, and finding you can calculate these series numerically on a computer by adding the terms together, getting more and more accurate as we add higher terms.

And then there is Fourier Series! The fact that you can add these trigonometric functions together, appropriately weighted, to make other functions, functions that look nothing like sines and cosines. And again, calculating these on a computer.

This is my favourite, the fact that you can add waves together to make a square wave.
But we can go one step higher. We can think of waves on a sphere. These are special waves called called Spherical Harmonics.

Those familiar with Schrodinger's equation know that these appear in the solution for the hydrogen atom, describing the wave function, telling us about the properties of the electron.

But spherical harmonics on a sphere are like the sines and cosines above, and we can describe any function over a sphere by summing up the appropriately weighted harmonics. What function you might be thinking? How about the heights of the land and the depths of the oceans over the surface of the Earth?

This cool website has done this, and provide the coefficients that you need to use to describe the surface of the Earth in terms of spherical harmonics. The coefficients are complex numbers as they describe not only how much of a harmonic you need to add, but also how much you need to rotate it.

So, I made a movie.
video
What you are seeing is the surface of the Earth. At the start, we have only the zeroth "mode", which is just a constant value across the surface. Then we add the first mode, which is a "dipole", which is negative on one side of the Earth and positive on the other, but appropriately rotated. And then we keep adding higher and higher modes, which adds more and more detail. And I think it looks very cool!

Why are you doing this, I hear you cry. Why, because to make this work, I had to beef up my knowledge of python and povray, learn how to fully wrangle healpy to deal with functions on a sphere, a bit of scripting, a bit of ffmpeg, and remember just what spherical harmonics are. And as I've written about before, I think it is an important thing for a researcher to grow these skills.

When will I need these skills? Dunno, but they're now in my bag of tricks and ready to use.

Sunday, 5 June 2016

A Sunday Confession: I never wanted to be an astronomer

After an almost endless Sunday, winter has arrived with a thump in Sydney and it is wet, very, very wet. So, time for a quick post.

Last week, I spoke at an Early Career Event in the Yarra Valley, with myself and Rachel Webster from the University of Melbourne talking about the process of applying for jobs in academia. I felt it was a very productive couple of days, discussing a whole range of topics, from transition into industry and the two-body problem, and I received some very positive feedback on the material I presented. I even recruited a new mentee to work with. 

What I found interesting was the number of people who said they had decided to be a scientist or astronomer when they were a child, and were essentially following their dream to become a professor at a university one day. While I didn't really discuss this at the meeting, I have a confession, namely that I never wanted to be an astronomer. 

 This will possibly come as a surprise to some. What I am doing here as a university professor undertaking research in astronomy if it was never my life dream? 

I don't really remember having too many career ideas as a child. I was considering being a vet, or looking after dinosaur bones in a museum, but the thought of being astronomer was not on the list. I know I had an interest in science, and I read about science and astronomy, but I never had a telescope, never remembered the names of constellations, never wanted to be an astronomer myself.

I discovered, at about age 16, that I could do maths and physics, did OK in school, found myself in university, where I did better, and then ended up doing a PhD. I did my PhD at the Institute of Astronomy in Cambridge, but went there because I really liked physics, and the thought of applying physics to the universe. With luck and chance, I found myself in postdoctoral positions and then a permanent position, and now a professor. 

And my passion is still understanding the workings of the universe through the laws of physics, and it's the part of my job I love (one aspect of the ECR meeting was discussing the issue that a lot of the academic job at a university is not research!). And I am pleased to find myself where I am, but I didn't set out along this path with any purpose or forethought. In fact, in the times I have thought about jumping ship and trying another a career, the notion of not being an astronomer anymore never bothered me. And I think it still doesn't. As long as the job is interesting, I think I'd be happy. 

So, there's my Sunday confession. I'm happy being a research astronomer trying to understand the universe, but it has never been a dream of mine. I think this has helped weather some of the trials facing researchers in the establishing a career. I never wanted to be an astronomer.

Oh, and I don't think much of Star Trek either. 

Thursday, 26 May 2016

On The Relativity of Redshifts: Does Space Really “Expand”?

I've written an article 'On the Relativity of Redshifts: Does Space Really "Expand"?' which has appeared in Australian Physics (2016, 53(3), 95-100). For some reason, the arXiv has put the article on hold, so you can download it here.


I like it :)

Sunday, 15 May 2016

How Far Can We Go? A long way, but not not that far!

Obligatory "sorry it's been a long time since I posted" comment. Life, grants, student, etc All of the usual excuses! But I plan (i.e. hope) to do more writing here in the future.

But what's the reason for today's post? Namely this video posted on your tube.
The conclusion is that humans are destined to explore the Local Group of galaxies, and that is it. And this video has received a bit of circulation on the inter-webs, promoted by a few sciency people.

The problem, however, is that it is wrong. The basic idea is that accelerating expansion due to the presence of dark energy means that the separation of objects will get faster and fast, and so it will be a little like chasing after a bus; the distance between the two of you will continue to get bigger and bigger. This part is correct, and in the very distant universe, there will be extremely isolated bunches of galaxies whose own gravitational pull overcomes the cosmic expansion. But the rest, just how much we can explore is wrong.

Why? Because they seem to have forgotten something key. Once we are out there traveling in the "expanding universe" then the expansion works in our advantage, increasing the distance not only between us and where we want to get to, but also between us and home. We effectively "ride" expansion.

So, how far could we get? Well, time to call (again - sorry) Tamara Davis's excellent cosmological work, in particular this paper on misconceptions about the Big Bang. I've spoken about this paper many times (and read it, it is quite excellent) but for this post, what we need to look is at the "conformal" picture of our universe. I don't have time togo into the details here, but the key thing is that you manipulate space and time so light rays trade at 45 degrees in the picture. Here's our universe.


The entire (infinite!) history of the universe is in this picture, mapped onto "conformal time". We're in the middle on the line marked now. If we extend our past light cone into the future, we can see the volume of the universe acceptable to us, given the continued accelerating expansion. We can see that encompasses objects that are currently not far from 20 billion light years away from us. This means that light rays fired out today will get this far, much, much larger than the Local Group of galaxies.

But ha! you scoff, that's a light ray. Puny humans in rockets have no chance!

Again, wrong, as you need to care about relativity again. How do I know? I wrote a paper about this with two smart students, Juliana Kwan (who is now at the University of Pennsylvania)  and Berian James, at Square. The point is that if you accelerate off into the universe, even at a nice gentle acceleration similar to what we experience here on Earth, you still get to explore much of the universe accessible to light rays.

Here's our paper 
 The key point is not just about how far you want to get, but whether or not you want to get home again. I am more than happy to acknowledge Jeremy Heyl's earlier work that inspired ours.

One tiny last point is the question whether our (or maybe not our) decedents will realise that there is dark energy in the universe. Locked away in Milkomenda (how I hate that name)  the view of the dark universe in the future might lead you to conclude that there is no more to the universe than ourselves, and it would appear static and unchanging, but anything thrown "out there", such as rocket ships (as per above) or high velocity stars, would still reveal the presence of dark energy.

There's plenty of universe we could potentially explore!