Posts Tagged‘gravity’

The Physics Faux Pas of The Force Awakens.

Before we get started let me just put this here:

LARGE PLOT SPOILERS BELOW FOR THE NEW STAR WARS MOVIE

There, now that’s out of the way let’s get onto the meat of this post.

Star Wars The Force Awakens

I, like all Star Wars fans, had been very much looking forward to the latest movie. Whilst I have my reservations about some aspects of it (which I’ll reserve for a conversation over a couple beers as to avoid a flamewar on here) I still thoroughly enjoyed it. However like most sci-fi movies The Force Awakens plays fast and loose with science. Following the rules of our universe when it suits the plot and sweeping them under the rug when it doesn’t. There are some grievances that I’m willing to let slide in this respect, this is fiction after all, however there’s at least one egregarious scene in which physics is completely thrown out the window when it really didn’t need to be.

My grievance lies with Starkiller base, the bigger and badder version of the Death Star which now encompasses an entire planet rather than just a small artificial moon. Whether such a device is something that could be built is something I’m willing to gloss over however the fact that it’s powered by drawing off mass from its neighbouring star brings with it a few niggling questions. It’s ultimate destruction, which then brings about the resurrection of its parent star, is also not something that would happen and not something I’d be willing to write off with space magic.

We get to see Starkiller base fire once and then begin preparations for firing again. Assuming that it didn’t travel to a new star in the interim (I don’t remember that being indicated as such) then it would’ve consumed half of its parent star’s mass to fire that single shot. That would’ve caused all sorts of grief for everything in orbit around it, not to mention the fact that that mass is now present on Starkiller base itself. Any asteroid or other debris near by should have rocketed down to the surface with incredible speed, laying waste to the surface. I’m willing to give a pass for a “gravity pump” or something else on the inside parts but being able to negate half the mass of a star over the entire planet is pure fantasy rather than a stretch of fiction.

However the final destruction of Starkiller base is the most egregious flaunt of the laws of physics. Putting aside all the mass contained within the star issue for a moment when it was all released the result would not be a new sun just like the old one. Whilst the mass was likely not compressed past its Schwarzschild radius (I’m assuming it’s a Sun like star) it would still be far too compressed to simply balloon back out. Instead it would likely become a white dwarf, that is if the explosion wasn’t violent enough to simply disperse the star’s material across its solar system. Since the system that Starkiller base resides in was never named I’m hazarding a guess it’s not relevant to the future plot so the returning sun just seems like a little bit of laziness more than anything else.

Of course I’m not advocating for 100% scientific accuracy in all films (indeed I don’t think there’s one good sci-fi epic that does) however a few nods here or there wouldn’t go astray. There are certain times where scientific accuracy would harm the plot and in that case I’m fine to relinquish it to induldge in the fantasy. Other times however it would do no harm and provide an interesting talking point as sometimes the physical reality can be far more interesting than the fantasy.

New Atomic Clock Almost Too Precise to be Useful.

Time is a strange beast. As far as we know it always appears to go forward although strange things start to occur in the presence of gravity. Indeed if you synchronized two atomic clocks together then took one of them on a trip around the world with you by the time you got back they’d be wildly out of sync, more than they ever could be through normal drift. This is part of Einstein’s theory of general relativity where time appears to speed up or slow down due to the differing effects of gravity on the two objects which results in time dilation. This effect, whilst so vanishingly small as to be inconsequential in day to day life, becomes a real problem when you want to tell super accurate time, to the point where a new atomic clock might be worthless for telling the time.

Sr-lattice-optical-atomi-clock_optMost atomic clocks in the world use a caesium atom to tell time as they transition between two states with an exact and measurable frequency. This allows them to keep time with incredible precision, to the point of not losing even a second of time over the course of hundreds of millions of years. Such accurate time keeping is what has allowed us to develop things like GPS where accurate time keeping allows us to pinpoint locations with amazing accuracy (well, when it’s not fuzzed). However a new type of atomic clock takes accuracy to a whole new level, being able to keep time on the scale of billions of years with pinpoint precision.

The Strontium Optical Atomic Clock comes from researchers working at the University of Colorado and can hold perfect time for 5 billion years. It works by suspending strontium atoms in a framework of lasers and then giving them a slight jolt, sending the atoms oscillating at a highly predictable rate. This allows the researchers to keep time to an incredibly precise level, so precise in fact that minor perturbations in gravity fields have a profound impact on how fast it ticks. As it turns out Earth is somewhat of a gravitational minefield thanks to the tectonic plates under its surface.

You see the further away you are from the Earth’s core the weaker its gravitational pull is and thus time passes just a little bit faster the further away you get. For us humans the difference is imperceptible, fractions of a fraction second that would barely register even if you found yourself floating billions of kilometres away in almost true 0g. However for a time instrument as sensitive as the one the researchers created minor changes in the Earth’s makeup greatly influence its tick rate, making accurate time keeping an incredibly difficult job. Indeed the researchers say that these clocks are likely to only be able to truly useful once we put one in space, far beyond the heavy gravitic influences that are found here on Earth.

It’s amazing that we have the ability to create something like this which throws all our understanding and perceptions around such a common and supposedly well understood phenomenon into question. That, for me, is the true heart of science, uncovering just how much we don’t know about something and then hunting down answers wherever they may lie. Sure, often we’ll end up having more questions when we come out of the end of it but that’s just a function of the vastness of the universe we live in, one that’s filled with ceaseless wonders that we’re yet to discover.

 

How Gravity Really Works.

We’re all familiar with the concept of gravity: 2 bodies of mass, no matter how or small and regardless of the distance between them, are attracted to each other. As a force it’s pretty weak, even when the two bodies are close to each other, as you can overcome the gravitic forces of an entire planet by simply standing up. However the fact that its range is unlimited and that it doesn’t appear to discriminate as to what it acts on is what makes it such a fundamental force in our universe.

Whilst that understanding is probably good enough for a general understanding of its mechanism of action it in fact is far more complicated and interesting than that and the following video is probably the best way of describing it I’ve seen in a long time:

It’s not a perfect simulation, as they mention in the video, but it does give you a really great insight into how the general relativity way of explaining gravity works and how it works with other well known theories like orbital mechanics. I reckon with a little additional engineering you could make something that functioned like a nearly ideal gravity field something which would be awesome in a science museum like Questacon here in Canberra. It’s still great in its current form though and hopefully we see similar things make its way into the science labs at our schools.

Gravity: An Amazing (Albeit Highly Unscientific) Film.

It should come as no surprise that my favourite movie genre is science fiction. Even though I was born long after the original Star Wars trilogy had finished watching it with my parents is still one of the fondest memories I have and that has long since bloomed into a passion for the genre. Of course this also feeds into my love of sciences as whilst I also enjoy fantasy, in all its forms, nothing quite compares to plausible futures that are based on real science. Whilst I understand that scientific accuracy will often take a back seat when the narrative requires it I can’t help but feel compelled to point out some of the more obvious flaws, especially when it’s such a big movie like Gravity.

Gravity 2013 WallpaperNow before I launch into this let me just be clear: I absolutely enjoyed Gravity. Whilst I was sceptical about George Clooney and Sandra Bullock being able to bring life to the roles they were given it didn’t take me long to warm to their characters. I was also very surprised by how much tension I felt for multiple different scenes, something which I don’t typically feel, at least not to that extent. All this, combined with the beautiful cinematography culminates in a movie that’s thoroughly enjoyable even if you take the hard line with science like I do. With all that being said though there are some points which bear mentioning and should have you not seen the movie I’ll advise you to skip reading on.

PLOT SPOILERS AHOY

The first thing that I, and several others, have taken issue with is the notion that from the orbit of the Hubble Space Telescope you’d be able see both the International Space Station as well as the Chinese Tiangong station (which is way more developed than current plans indicate, but that’s another story). Even if all of them shared identical orbits, which they don’t, the Hubble is in an orbit that’s some 200KM above the ISS and Tiangong making any naked eye visual impossible. Following on from this the idea that you’d be able to then travel between them becomes somewhat difficult as the energy required to do the plane change manoeuvres would be far above the capabilities of Manned Manoeuvring Unit. Indeed the backup plan NASA had for a shuttle that had suffered a catastrophic failure event such as the one in Gravity was to send another shuttle up there to rescue them, dubbed STS-400, which was the reason why we saw 2 fully fuelled shuttles on their respective launch pads the last time we serviced the Hubble.

I’m sort of able to forgive that for the sake of story however one moment that I won’t was when Bullock is holding onto Clooney’s tether and he says he has to let go or they’ll both be doomed. You see at that particular point there’s no more forces acting on them as once they got tangled up and stopped moving all their momentum had been transferred to the ISS, rendering them at equilibrium. If Bullock had simply tugged on the tether slightly Clooney would have then started drifting lazily towards the ISS and Bullock could have pulled herself back along the parachute cords. I would’ve let that slide if it was a minor side point but it’s one of the main turning points of the movie and unfortunately it just has no basis in reality whatsoever.

One thing I was also going to pan Gravity for was the use of fire extinguishers as thrusters since I figured the amount of delta-v available in them wouldn’t have been enough to provide any meaningful thrust. As it turns out, depending on what kind of extinguisher you have, there could be as much as 100m/s in them, a heck of a lot of thrust by any means. Whilst you’d be far more likely to send yourself into an unrecoverable spin if you were using them in the way shown in Gravity it does lend some credence to the idea of using it to correct your trajectory in order to intercept something else.

PLOT SPOILERS OVER

There were also numerous other minor details but compared to the previous few I mentioned I don’t think they’re worth digging into. Whilst there really were some cringe inducing moments from a science perspective it is a highly enjoyable film, even if you’re not into the whole space scene. It’s also worth it to see it in 3D, something I don’t say often, as the producers have taken care to use 3D as a tool rather than slapping it on in order to increase the ticket price. It might not be super hard sci-fi but then again not many films are and ones of Gravity’s calibre are even rarer.

 

What Water On The Moon Means For Space Exploration.

The moon is our closest celestial neighbour and as a consequence is by far one of the most studied celestial bodies. By all accounts it’s a barren wasteland, covered in numerous pot marks from the asteroids that have bombarded it over its lifetime. However the more we investigate it the more we find out that, whilst there’s almost no chance of life being present there, many of the resources that life depends on can be found there. Whilst we’ve known for a while that it would be possible to extract water from the regolith on the surface new observations from NASA’s Moon Mineralogy Mapper instrument aboard India’s Chandrayaan-1 have revealed that there might be actual water on the Moon, just waiting there for us to use.

india-chandrayaan-1-spacecraftThe initial implications of this are obvious. Water is one of the fundamental resources required for any human based space mission and the amount required usually has to be brought along for the ride. This means the payload capacity used for bringing water along can’t be used for other things, like additional supplies or more equipment, and presents a big challenge for long duration flights. Having a source on the Moon means that any potential bases or colonies established there would have much less reliance on resupply missions from Earth, something which is the primary limiting factor for any off-world colonies that we attempt to establish.

However that pales in comparison when compared to what water on the Moon means for space in general: it’s a primary component for rocket fuel.

Water’s basic composition is hydrogen and oxygen which are the components which power many of the liquid fuelled rocket engines that operate today. Of course in their bonded state they’re not a ready to use propellent exactly so a process is required to break those bonds and get those atoms separated. Thankfully such a process exists, called electrolysis,  which splits water down into its component gasses which can then be stored and later used to send rockets on their way. Of course such a process relies on a stable power source which would likely be some like of large solar array backed up by a large battery bank to last through the 2 week long darkness that regularly blankets half the surface.

The biggest challenge that many of the long duration or large payload missions face is the fact that they require more fuel. Carrying more fuel unfortunately also means carry more fuel and there’s points of diminishing returns where you’re spending far too much fuel just to get yourself out of our gravity well. Having a refuelling station or the Moon (or, even better, constructing and launch payloads from there) would mean that we would put larger payloads into space and then push them to the outer reaches of the solar system without having to waste as much fuel to get ourselves out of Earth’s gravitational influence.

Of course seeing this kind of technology implemented is some ways off as it seems like NASA’s next target will be a flag planting mission on Mars. Such technology would be quite applicable to Mars as well seeing as the soil there has a lot of trapped water (and there’s plentiful water ice pretty much everywhere but the equatorial region) but it’d be far more valuable if it was implemented on the moon. In either case I believe this is foundational technology that will be pivotal in humanity pushing itself to the far reaches of our own solar system and, maybe one day, beyond.

 

The Weird and Wonderful Effects of Microgravity.

Life on Earth evolved in a never ending battle to be the most well adapted species to its environment. Consequently it can be said that the life forms that evolved here on Earth are specialist biological machines with certain requirements that must be met in order for them to thrive. It then comes as no surprise that entire species can be wiped out by small changes to their environment as their specific adaptations no longer provide them the advantage that they require. However there’s one particular pressure that all life has evolved with that, at least for most life, will never change: gravity.

Many biological processes rely on gravity in order to function correctly and for the longest time it was thought that no life that evolved here on Earth could survive a zero/microgravity environment for long. Indeed medical doctors back on the Mercury program were very sure that the second their astronauts went into orbit their vision would blur, rendering them incapable of performing any tasks. The truth of the matter is whilst we’re designed to work well in our standard 1G environment our bodies can cope quite well with microgravity environments for extended periods of time, provided certain precautions are taken.

What’s truly fascinating to watch though is how other creatures function without the aide of a constant gravitic pull. Indeed quite a lot of science done aboard the International Space Station has been centred around studying these effects on varying levels of creatures and some have produced very interesting results. For example spiders sent up to the ISS don’t spin webs like their Earth bound relatives do, they instead weave what looks like a tangled mess all over their environment. It would seem that their sense of direction heavily relies on figuring out which was is down and absent that their webs lose their usual symmetry.

Other animal species seem to adapt rapidly to the loss of gravity’s unrelenting effects. Mummichogs, a type of small fish, appear to be quite hardy little creatures in microgravity environments. They suffer some initial confusion but after a short while they appear to be quite capable of swimming perfectly well in microgravity. Ants too seem to adapt rapidly to the loss of gravity with their nests taking on an almost surreal structure that is not like anything you’ll see on Earth. The habitat that NASA designed to take ants into space is also quite incredible being a clear blue gel that contains everything the ants need to survive both the trip up and life aboard the space station.

Incredibly some species appear to be  better suited to microgravity than the regular 1G environment on Earth.  C. Elegans, a type of unsegmented worm, not only adapted to life in space but showed a marked increase in life span over their earth bound cousins. The cause appears to be a down-regulation of certain genes associated with muscle ageing which in turn leads to a longer life. Whether the same genes could be down-regulated in humans is definitely an area for investigation but as everyone knows us humans are far more complicated beasts than the simple  C. Elegan.

Indeed whilst muscle atrophy is one of the biggest problems facing astronauts who spend a long time in space there are several more concerns that also need to be addressed. Unlike the C. Elegan we humans have an internal skeleton and absent the effects of gravity it tends to deteriorate in much the same way as it does in bed ridden patients and people with osteoporosis. Additionally whilst the ISS is still within the protective magnetic field of Earth it’s still subject to much higher levels of radiation than what we get here on Earth which poses significant health risks over the long term. There’s also a whole swath of things that don’t quite work as intended (burping in microgravity is fraught with danger) which we’re still working on solutions for but suffice to say if we’re ever going to colonize space reproducing the effects of gravity is going to be one of the most critically required technologies.

It’s not often that we get the opportunity to effectively remove a unyielding constant and then study how much it influenced the development of life here on Earth. This is one of the reasons why space based research is so important, it gives us clues and insights into how dependent our biological processes are on certain key variables. Otherwise we’d figure that gravity was simply a requirement for life when now we know that life can survive, and even thrive, in its absence.

My Smart-ass Subconscious.

I’ve often found that trying that sticking with a problem from start to finish is usually the least efficient way of getting it completed. Quite often if I take a 1 hour break whilst I’m in the thick of trying to solve something I’ll usually figure the answer out before I return, being able to move onto the next bit of work in far less time than if I had tried to struggle my way through. I think this is the main reason why the lawn gets mowed routinely during he summer months, that 30 mins~1 hour of basically mindless work let’s my subconscious tackle the problem in ways that I can’t do normally.

The most recent example I can think of was the problem of producing realistic gravity in the game I’m developing with a good friend of mine. I’ve had the basic gravity mechanics working for ages and even managed to get a planet into a near-circular orbit around a star. Unfortunately from there finding other stable orbits for varying distances and masses proved to be quite troublesome as there didn’t seem to be any kind of simple relationship that I could derive that would produce the same circular orbits as I had achieved after tinkering around with initial forces for a couple hours.

It’s been a real pearler of a problem too as whilst I’ve been able to make steady progress despite this (my one little test planet is enough to get most things working) I still couldn’t figure out how to give a planet a stable orbit based on its mass and initial distance from the sun. I tried many different things, from trying to map an equation based on a couple stable orbits to pushing the planet around so it would stay on course (which hilariously flung planets out of sight). Then late one night just before I was about to fall asleep it hit me: I could use the force that was being applied to the planet by the sun as the magnitude for the initial force. I then just have to work out the components along the desired orbital trajectory (breaking out some good old fashion trigonometry) and I should be on my way. I haven’t tested this yet, but it’s the only idea I’ve had that hasn’t involved fussing around with variables for hours on end.

It’s that same process that jolts you awake in the middle of the night with that name that you couldn’t remember or that fact you were trying to come up with at a crucial time. I find it really intriguing as I obviously have the ability to solve these kinds of problems somewhere in my head however I just can’t have it on tap, I’ve just got to let my brain do its thing whilst I wait around for the solution.