Category: Physics


When we’re little (and in some strange cases, into adult hood), the story of Father Christmas, the fat old man adorned in red and white robes, pervades our lives, (hopefully) making us think about our actions due to the threat of being branded a “naughty child” and getting coal as a present instead of that new PlayStation game you really wanted. However, there comes a time in every child’s life where they learn the truth of Christmas. The truth that an old man doesn’t break into you’re house, leaving gifts, but that instead your parents quietly hide presents in the loft until you’ve gone to sleep on Christmas eve.

And for those of you that still believe, sorry, but the truth hurts.

But, as a bit of an annoying child, one thing always puzzled me, if this legendary man DID exist, how would he get around the world, and all its good children, in only one night? would it even be possible?

Well lets start with the children. There are roughly 2 billion under 15’s on earth at any one time (lets assume this is the point you stop believing in farther Christmas and start buying people gifts instead, you cheapskate). However, since St Nick does’t visit children of Muslim, Hindu, Jewish or Buddhist (except maybe in Japan) religions, this reduces the workload for Christmas night to about 33% of the total, around 660 million children, and with a global average fertillity rate of around 2.5 children per woman (and therefore household) this amounts to about 250 million households, assuming there is at least one good child in each.

Now, farther Christmas has circa 31 hours (if we include things like the rotation of the earth and differing time zones) to make his round trip of the world and its homes, this works out as 2240 visits per second. That is to say, St Nick has around 1/2500 th’s of a second to park up on your roof, break into your house, fill your stockings, place your presents, eat any food left for him, get out again and reach the next house.

Assuming these 250 million homes are evenly distributed around the world (which, of course, they wouldn’t be), we’re now talking 0.23 miles per household, a minimum trip length of 131.1 million miles, without diversions around storms, aeroplanes or mountains.

This means our dear old Father Christmas has to be travelling at a speed of around 1175 miles per second (4,226,000 miles per hour) this is about 5500 times the speed of sound. In comparison, the fastest ever man made object is the Helios space probes, which orbit the sun with an average speed of 44 miles per second, your run of the mill reindeer can run at about 0.00416 miles  per second (15 miles per hour).

The payload of the sleigh adds another interesting element. Assuming that each child gets nothing more than a medium sized LEGO set (two kilograms), the sleigh is carrying over 500 thousand tons, not counting Father Christmas himself. While on land, a conventional reindeer can pull around 150 kilogrmas. Even granted that flying reindeer can pull 100 times this, St Nick would need more than 8 or 9, he would need 33,000 of them. This increases the payload even further, adding another 5000 tonnes to the sleigh. This makes it similar in weight to the Seawise Giant, the longest ship ever built, and by many standards, the largest man made, self-propelling object ever.

500,000 tonnes moving at 1175 miles per second is going to produce a lot of air resistance. It would be equivalent to a spacecraft re-entering the earth’s atmosphere 168 times faster than its supposed to. As a result, the reindeer would almost instantly evaporate into a superheated cloud of atoms and molecules.

Not that it matters much, since St Nick, as a result of accelerating from a dead stop to 1175 miles per second in 0.0004 seconds, would be subjected to acceleration forces of 22 million g’s. A 115 kilogram Father Christmas (which seems ludicrously slim) would be pinned to the back of the sleigh by 217 million newtons of force, instantly crushing his bones and organs and reducing him to a quivering blob of pink goo.

Therefore, if Father Christmas did exist, he doesnt now.

Hope you had a good Christmas, and happy new year!

Alex Davis

References:

http://www.indexmundi.com/world/demographics_profile.html

http://worldchristiandatabase.org/wcd/

http://www.un.org/esa/population/

New Eyes on the Sun: A Guide to Satellite Images and Amateur Observation by John Wilkinson

http://www.tribuneindia.com/1999/99jul11/sunday/head3.htm

What is Doppler shift and how does it affect the world around us and how using it as an excuse for running that red light may not be such a great idea

If you go and sit out on a not to busy road on a reasonably quiet day, you may notice, that as cars drive past, that the noise they produce seems to differ in pitch depending on whether they’re travelling away or towards you. It seems as if, when approaching you, that the car emits a higher pitched sound, and as it travels away, a lower pitched sound. This strange phenomenon is known as Doppler shift, or the Doppler Effect. It’s caused by waves becoming squashed up in front of a moving object, as the emitted waves struggle to pull away, and becoming spaced out behind the moving object, as the waves struggle to keep up, in both cases changing the pitch of the sound, or frequency of the light, as the wavelengths become shorter and longer.

The basic equation of low speed Doppler shift is:

Where c is the speed of the wave, vr is the speed of the observer, vs is the speed of the emitter and f0 is the frequency of the emitted wave.

This idea was first proposed by the Austrian physicist Christian Doppler in 1842, his paper “”Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels” (On the coloured light of the binary stars and some other stars of the heavens) it details the effects of heavenly movement of the frequency of light received from observable stars. Basically, how the movement of stars in relation to earth affected the colour of the observed light. This technique of observing the difference between the expected frequency and actual frequency of light emitted by stars and galaxy’s has very useful applications. It allows astronomers and cosmologists to determine the rate of expansion in the universe by measuring the “red shift” of galaxy’s, how much the their observed light has been shifted towards the red end of the spectrum due to their movement away from us.

Now this is all well and good, but what does this all mean for us, average Joe, not Johnny the astronomer, and how can we use it to our advantage? Well the thought occurred to me recently, how fast would you have to be going to see a red traffic light as green? It’s an interesting thought. Imagine you’ve just been pulled over for running a red light on a busy box junction, nobody was hurt, but the police still saw you. How fast would you have to be traveling for the light to have appeared green to you, and thus, to get away with the minor traffic offense on a technicality? Well, we can’t use the equation we saw earlier as there are several inherent problems with it. Firstly, it only works for slow speeds, and as is plainly obvious, we’re going to have to be travelling at some speed before things start changing colour, and secondly, it only works accurately for sound waves, or waves that have to travel through a medium, unlike light which can travel though a vacuum. So, we have to use another equation, this time the Relativistic Doppler effect equation, which takes into account the speed of light so it doesn’t affect our calculations as much.

And with some fancy rearranging, this becomes

Now add in some numbers

And we come out with a speed of around the third the speed of light, which is speeding by anyone’s standards. So, you may get away with one traffic offence on a technicality, but there wouldn’t be much hope of getting off on this one.

N.B. see https://journalclubscienceblog.wordpress.com/2012/07/17/what-would-happen-if-we-travelled-near-the-speed-of-light/ for another reason why this isnt a good idea

By Alex Davis

Sources-

http://en.wikipedia.org/wiki/Relativistic_Doppler_effect

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html

http://en.wikipedia.org/wiki/Frequency

Advancing Physics AS text book

A calculator

A Game of Swords

After reading far too much of the excellent Song of Ice and Fire series, I decided to look a little deeper into the knight’s best friend: A sword! I will not only be looking at the techniques used to create some of history’s most notorious weapons, but I will be exploring the physics behind them, from molecular structures to forces and pressure. This is A Game of Swords!

Anyone who’s anyone (when it comes to weaponry) knows that the most important part of any edged weapon is the quality and design of the blade. There’s no point slashing at your opponents with blunted edges, and you’ll never pierce anything if you have an inferior tip, so how can we go about ensuring that our sword is going to start sharp and stay sharp? The first thing to look at is the material you are using. The most ancient swords, used by the Mayans and Aztecs, were little more than wooden clubs with obsidian chips laid along each edge. Obsidian, made up of Silicon Dioxide with mixed oxides of Magnesium and Iron, is a more a metallic glass than a pure metal. It is this glass like quality that makes it great for sword making, as it is extremely brittle, and will fracture into very sharp pieces. This is all very well, if you happen to live near a long dead volcano, but for the tribes-people of Europe there had to be another way to forge a weapon. The ancient Greeks relied heavily on bronze weaponry, as this alloy of Copper and Tin was strong, sharp and easy to make. Due to the metals used, it was very easy to cast and forge into weaponry. Even late into the iron age, Roman officers carried finely decorated bronze swords into battle. The eponymous Roman sword is the Gladius, which was a very simple double-edged blade with a (relatively long) sharpened point. These swords were primarily designed for underarm stabbing, as in the heat of battle there is very rarely enough space to swing anything larger than a shortsword! The Gladius and its cavalry equivalent, the Spatha, dominated the battlefield for centuries, allowing the Romans the flexibility that they needed, as it only used one hand, the famous rectangular roman (or its rounded sister for mounted combat) shield could be held in the other, offering ample protection for infantry and cavalry alike.

The blades of the common soldiers were actually cast from iron at first, as the early methods of casting it created rather brittle weapons that were prone to breaking. Iron was however much more abundant than copper and tin, and smithies soon started pioneering new techniques to create stronger blades. In East Asia, the metal was often forged from special Tamahagane steel, made from different mixtures of iron sand, which creates an incredibly strong mixture of alloys, perfect for each individual part of the blade. This steel was then folded upon itself repeatedly, creating an edge sharp enough to split a bullet in two (http://www.youtube.com/watch?v=OBFlYwluqMk – skip to about 45-60 seconds to see the slo-mo footage). Steel is so strong because of its crystalline structure, which is created when molten iron is mixed with Oxygen. This is because iron ore contains a lot of carbon atoms. When the iron is cast it will lose some of these carbon atoms, but the more there are, the more brittle the iron becomes. By controlling the amount of oxygen that flows across the steel, the hardness and potential sharpness can be controlled, allowing the smithies to tailor-make their raw forging material. If the steel is more malleable, it can be forged into a stronger weapon, with more interesting curves, but may blunt a lot quicker. In this way a sword can be made from composites of flexible and inflexible steels, with sharp, brittle edges and a flexible body. This is the point at which sword making reaches its zenith.

But now we have our alloys, how do we decide what sort of sword we want? Should our sword be held in one hand, or two? A light sword is good, but would a heavier sword cause a more devastating blow?  The answers to these questions are largely situational, but there may be a physical reason to choose one weapon over another. It all comes down to how much pressure you can apply, and how much pressure your opponent can resist. Pressure is simply the force applied, divided by the area that it is applied to, so greater force equals greater pressure, right? But the force in a sword swing comes mainly from momentum (and therefore the weight) of the sword. So if we want a greater force we’ll need a bigger sword, but a bigger sword means you’ll need to be stronger to actually do anything with it. This is all very well if you’re the knight with the rippling muscles, but what if you’re the poor gangly footsoldier? In that case, would it not be easier to reduce the area that the force is applied to? Especially if your opponent is wearing plate armour and heavy chain-mail, you’ll need something that has a chance of piercing through all those layers (and hopefully your opponent). This is where pointing swords, such as the Rapier come into play. These allow a great deal of pressure to be applied by stabbing forward with the tip of the sword. The smaller and sharper the tip, the greater piercing power your sword has, and the more likely your enemy is to get a bellyful of steel! most of these swords still had two sharpened edges, just in case, but occasionally, a soldier would be so confident of his thrust that his sword would have no edge at all!

Let us suppose we have our stocky knight in his heavy plate armour, with a big, heavy broadsword. On the other side of the field we have the gangly footman, épée in hand, dressed in some cheap chain-mail and an ill-fitting helmet. The knight is a sure bet, right? Wrong! Let us say that the knight’s armour can withstand a direct hit of 2000 pascals of pressure on his breastplate. In anyone’s terms that’s an awful lot of pressure. Now the footman’s épée has a finely crafted tip, 0.5 millimetres across, and his sword weighs about a kilogram. Our footman, quick as an arrow, lunges at our knight with an acceleration of  10 metres per second per second. Newton’s second law states that F=ma, so our footman hits the knight with a force of 10 Newtons. That might not sound like a lot, and in everyday terms it isn’t, but when we feed this value into our pressure equation (bearing in mind the standard length unit is metres), we get a value of 20000 Pascals! Ten times more than the knight’s armour can withstand! Needless to say, the footman would need to give his sword a bit of a clean before he sheaths it again. The outcome might have been different if the knight hadn’t been encumbered with such a heavy broadsword, and indeed, when using a heavy weapon it is always best to be accurate, and better to be well prepared!

Thus we have seen how versatile the humble sword can be, ever the choice of officers and laymen alike, the humble blade served us well for thousands of years. We can see that swords, as well as strategies, can be adapted to suit any situation, and now know that as long as your blacksmith is good enough, you’ll never go unarmed or unprepared!

Harry Saban – The Octave Doctor (Phd Pending)

Sources:

Wikipedia (We’ve all done it, so don’t judge me!) – History of Swordmaking and Steelmaking.

http://www.ehow.co.uk/about_6638014_atomic-structure-steel.html – Atomic Structure of Steel

The Higgs Boson was named after an Edinburgh physicist, Peter Higgs. It is often thought that the Higgs boson forms an overwhelming majority of the composition of the answer to the question of how matter has gained mass. To those of us in agreement with the popular theory of the Big Bang as the origin to the universe, it is thought that shortly after the beginning of the cosmos, mass was inexistent. Indeed, nor were atoms and elements, but that is a different story. A field known as the Higgs field is thought to be the reason for the existence of mass – particles interacting with this field gain mass. This came about due to the decrease in the temperature of the universe (below a certain threshold value), and the amount of mass is directly proportional to the strength of the interaction between the particles.

In the 1970s, it had come to the attention of the global physics community that two of the fundamental forces were actually very closely related. The thing is, the proposed explanation for a unified force, namely the electroweak force, required that a field exist, whose constituent particles carry no mass. Unfortunately, it is known now that this is untrue, and so Higgs and his colleagues set about finding a solution.

Ian Sample has conveniently created an analogy using, rather imaginatively, ping pong balls, food trays, and brown sugar. Basically, as the universe was formed, a field known as the Higgs field came into existence. Many particles interacted with this field, and the more they interacted, the heavier they became, and no longer moved at the speed of light. The Higgs boson is analogous to a grain of sugar, i.e. the constituent of the Higgs field. As you may know, just like light itself, which has dual properties of wave and particle, so may the boson. The question scientists endeavour to answer is how a particle whose properties are yet to be ascertained, could be the reason behind the existence of mass. Sample conjectures that amongst other products from a collision between protons travelling at 0.999999c, Higgs was one of them. The problem is, unlike most other particles, such as photons, quarks, electrons etc., the Higgs boson decays very quickly, and as such is very difficult to observe. The standard model of the universe, developed in the 1970s, which is used today, has met unprecedented success over the past decades in having aspects of it being proven to exist, aside from links to gravity. However, the fundamental tool that is needed was the proof of the existence of the Higgs boson.

The 4 fundamental forces of nature

Why is it called the boson? Well, earlier I mentioned the electroweak force, a force unifying electromagnetism and the weak nuclear force from the standard model, which in itself contains the four fundamental forces – gravity, electromagnetism, and the strong and weak nuclear forces. Scientists propose that each of these forces has a carrier particle, collectively named the boson, which interacts with matter. For example, the electromagnetic force has the photon as its boson, which carries the electromagnetic force with it, and transfers it to matter. Bosons are believed to be able to snap back in and out of existence in an instant and also be ‘entangled’ with other bosons around them. You see, this boson is not only a ‘fundamental force carrier’, it is also a term used for force carriers of various natures and designations. As a conveniently relevant example, I can explain the significance of the photon and bosons called the W and Z particles.

Going back to one of the constituents of the electroweak force, the weak force, its force carrying particles, as the photon is for the electromagnetic force, are two bosons named W and Z, discovered in the 1980s. Unlike the photon, these do have mass. A possible analogy for this next part is to think of these force carrying bosons as balls that are exchanged as particles exchange these force carriers to observe the weak force. Heavier balls have a lower throwing range, and similarly, so do heavier force carriers – this was known. But what gives these force carriers mass, which affects their behaviour? The Higgs theory. This is what scientists think could account for this fundamental difference between photons and the  W and Z bosons, and, by extrapolation, for all other force carriers with nonzero masses. It has been estimated that 96% of the universe is invisible, made up of dark matter and physics that have not yet travelled within our grasp. The Standard Model only accounts for the 4% of the universe which we know so well, hence why we know it can never be a complete, unifying theory. For this, we need to be able to build on the concept, much like Einstein built on his theory of Special Relativity in order to account for gravity – which, incidentally, we are able to conclusively explain very little of. So in reality, the quest for the single Higgs particle (in this specific context) includes determining whether it is a Standard or Non-Standard Higgs particle.

The Standard Model Higgs particle would, if confirmed to be true, only one of numerous different types of Higgs particles. In order to gain an insight into the sheer complexity of the process and the need for excruciatingly thorough and systematic procedural protocols, consider the following. One of the possible ways a Higgs particle can decay, as it will within an instant of being detected, is by emitting two photons, which can be detected. However, there are so many other two-photon events that occur, which by themselves have had countless statistical analyses carried out on them in order to determine various values, some simple ones being the percentage of decay events leading to two photons being produced. Not only this, any discovery can only be (tentatively) validated if the confidence levels from data have a discrepancy of less than one in a million.

I hope that my chaotic and quick run through the world of Higgs has, if not invoked interest, at least informed you in an understandable manner. For those who are interested, the analysis of the Higgs boson’s (possible) discovery is scheduled to be completed by the end of 2012, for which time we should not only be hoping to know whether the Higgs particle that had been discovered is Standard or Non-Standard, but also whether it exists at all. Despite the disappointment that will no doubt be experienced by the disproval of the Higgs boson’s existence, each of the three possible outcomes will lead to progress, either building on current proven theories, adding flesh to the bones of hypothetical theories, or starting afresh in order to encourage the development of entirely new concepts altogether, which may or may not be more effective than building on our current ones.

Sources:

Bharat

Made for my Nuffield Bursary work placement.

Sorry for not posting for the last couple of weeks but things got rather hectic at work. Good news is, we’ve got some really interesting results, and my supervisor will be presenting them at a conference in Germany in October! If anything gets found then I might be a co-author on the paper. It’d be nice to be published before I got into university! If you guys want a special blog post all about the work I’ve done then let me know and I’ll put something together.

– Harry Saban – The Octave Doctor (Phd pending)

This week Harry’s been hard at work in the University of Hertfordshire, desperately searching for brown dwarf binaries and handling huge clumps of data in a room with no windows. He hasn’t seen sunlight in days, and is turning into some kind of astronomical mole-man. Will he find his pair of stars? Will he get to see sunlight? When did he start writing these little intros? Who is Keyser Soze? Read on to find out…

Monday-Tuesday (Attack of the Spreadsheets)

Who’d have thought that GCSE ICT would come in so handy? The past couple of days have presented me with such functional gems as “=AND(IF(BC4<3,1,0),IF(BF4<3,1,0),OR(AND(IF(BJ4>3,1,0),IF(BJ3>3,1,0)),AND(IF(BK4>3,1,0),IF(BK3>3,1,0))))”,
“=((F7+J7)/2)*(AV7/1000)*4.74” and the catchy little number “=10^((I6/5)+1)”.

Most of my days at the moment are spent on LibreOffice Calc, which is the Linux version of Excel. This means that it is free and it runs very smoothly, but occasionally the functions can go a little bit mad. I’m still having trouble trying to convince it that the cosine of 90° is 0, not 1.457849384E-17. So far I’m not doing very well, but hey-ho!

Wednesday-Thursday (Marvellous Magnitudes and Magical Moduli)

All this spreasheet manipulation hasn’t been in vain though, as we’re finally whittling down the list of candidate stars into something a bit more manageable. If last week was all about proper motion (and it was), then this week is all about colours, magnitudes and distance moduli. These things are essential for working out how far away from us a star actually is. After we’ve done this for a pair of stars, we can then calculate how far away they are from each other! Firstly, we have to consider the different “bands” that the star has been seen in. There are a great many bands of colour, through infra-red into visible and beyond, and these are labelled with letters from the alphabet, but not in alphabetical order (because scientists love to make things difficult). These bands are given as one letter minus another, for example “I-Z” or “J-H”. This is because the light is measured at a certain brightness in the J frequency, then a certain brightness in the H frequency. We can then see what the difference is to give us a band between these two frequencies. From these bands you can then find out the Absolute Magnitude of a star (this is the measurement of how bright a star would be if viewed from 10 parsecs* away, and allows us to have a well defined base value for the brightnesses of all stars) by matching the colour to a star of known magnitude on a chart. This was pretty laborious work, as I had over 200 separate entries, that I had to do twice (for reasons I will explain next week). As you can imagine, this took me a good day of estimating and eye-strain, but it was worth it in the end. Soon we had values for the maximum and minimum absolute magnitudes.

I then needed to get the Distance Modulus. This is a very important number that we use to work out the distance to a star. Luckily it’s really easy to work out! All you do is subtract the absolute magnitude from the apparent magnitude (how bright the star appears to be for us here on earth**), and viola! It’s then a simple matter of dividing it by five, adding one and putting 10 to the power of your new number. This gives you the distance to the star in parsecs, and since the scale is logarithmic (in powers of ten) a small difference in the modulus can make a very big difference in distance! Magnitudes are also logarithmic, so small differences there can make large differences later on. Basically, for such massive objects (stars and the like) you have to be ridiculously precise!

Once the distance has been worked out it takes some simple trigonometry (distance x angle of separation in arcseconds) to find out how far apart the stars are in real space! You can then begin to think about how likely it is that the stars are related, as the bigger the separation, the less likely they’re a pair. Often these objects are many thousands of Astronomical Units (distance from earth to the sun) apart, but some can still be linked together. It’s fantastic to think of two stars, so far apart, yet still whirling through the cosmos as a pair, inescapably linked by nothing more than the forces of gravity. Some of the distances are enough to make your head spin a little, though. In astronomy everything is (surprise-surprise) astronomically big!

It’s enough to make a chap want to take a siesta with a nice glass of Pimms, eh? Chin-chin!

Harry Saban – The Octave Doctor (Phd Pending)

*A parsec is an astronomical unit of distance measured using some clever trigonometry. As you should know, the earth goes round the sun, and this causes stars that are nearer to us to appear to move, relative to the stars that are very far away. This is called the stellar parallax and is used to work out parsecs and the difference is greatest every half a year, because the sun is on the opposite side of the “circle”. If a star appears to move one arcsecond in the sky, it is one parsec away. This means it forms a sort of triangle, with a baseline that is 2 AU wide, and a height of 1 parsec. Wikipedia has some good diagrams, if you’re finding this a bit tricky to visualise (it’s pretty odd).

**Or more precisely, from a satellite orbiting the earth. The brightness would be affected by the atmosphere down here on earth by all those pesky gas particles up there making mischief and generally having a whale of a time.

Fun times with Space-Time

Good news everyone!

 

Einstein as we know was a brilliant man (but as it turns out not a outstanding student), producing E=mc2, the general and special theory of relativity and much more. I will be discussing one of his concepts – space-time.

 

Imagine a big trampoline in front of you. You place two bowling balls – one big and one small – on the trampoline apart from each other, you notice that the bowling balls make an indentation on the elastic surface; the bigger of the two balls causing a bigger indentation than the smaller. Now suppose you roll a tennis ball along the trampolines elastic surface, you’ll see that the path of the tennis ball is deflected by the indentations made by the bowling balls. In basics the trampoline’s surface represents space-time, the bowling balls represents stars or planets and the tennis ball – light.

 

You are probably exclaiming, “This is preposterous! We were told that light only travels in straight lines!” well for daily life this is true as the bending of light due to a house or that annoying child on his scooter is so small that it is unnoticeable, however on the scale of stars and such, it is quite a noticeable deflection. This analogy has some flaws such as forces that are acting on the tennis ball which would not affect light (friction and so fourth) but mainly that the trampoline gives the impression of space-time being flat whereas it is actually all around us. We can’t say that matter directly affects the path of light just that it affects space-time, which in turn affects light. From this it is reasonable to assume that light would have to slow down from being curved around a sun, but light is travelling at a constant speed therefore we can conclude that gravity slows down time!

The bending of space-time due to a large mass

Sir Arthur Stanley Eddington first proved this light bending in 1919 when he observed a solar eclipse in Principe (near Africa) taking pictures that showed the deflection of light from star passing by the sun which in normal circumstances are obscured by the Sun’s brightness. He compared them to pictures of a star when not in the presence of the Sun and showed an obvious deflection that showed conclusive evidence that General Relativity trumped the Newtonian World.

 

 

There is a particular type of star that has such a great mass that it creates a ‘well’ in space-time, a Black Hole. As a lot of you will know a black hole is a star that has a sufficient mass that it collapses in on its self where no light can escape. This mass warps space-time so much that it can be thought of as to fall into space-time or create a ‘well’ in it (see picture). The rim of this ‘well’ is the event horizon where the bending of light is so great that it falls into the ‘well’. If we were to use the trampoline analogy then it would be like putting a bowling ball of incredibly high mass (assuming the elastic sheet was unbreakable and the trampoline was very high up). A black hole’s great mass means that we could use it for time travel. As I have already mentioned gravity can slow down time, therefore if we managed to maintain an orbit around a black hole without being sucked in we could theoretically age slower than somewhere else, lets say Earth. So when we returned to Earth we would be further in the future than if we had stayed on Earth.

A black hole creating a ‘well’ in space-time

 

 

 

 

 

 

This great mass and curving of space-time also opens up the possibilities of wormholes (a hole that links two points of space). It supposes that two black hole ‘wells’ could join together and make a tube in space-time linking these points in space. However the chance of this happening is miniscule and if it did happen there is the problem of maintain this link.

Wormholes can be used to cross great distances in space

 

I hope you have enjoyed my blog that has touched upon the brilliant concept of space-time!

Christian Tuckwell-Smith – Farnsworth

 

Sources:

Stephen Hawking – A Brief History of Time

http://en.wikipedia.org/wiki/Arthur_Eddington

http://www.youtube.com/watch?v=f0VOn9r4dq8

http://www.youtube.com/watch?v=WHRtdyW9ong

Monday-Tuesday

I rolled up at the University of Hertfordshire eager, ready and prepped for a hard day of work. I’d tried to conceal the bags under my eyes from accidentally getting ready an hour before I needed to (Reading emails properly has never been my strong-suit) and grinned a slightly weary grin. Then the day really began. There was the requisite meet-and-greet with the head of department Dr Pinfield, and he showed me and the other couple ofstudents around all the various bits of the department we’d be getting to know quite well. Namely, the room with our desks in and the canteen. As I saw the postgraduates sitting in front of computer screens covered in lines of coding I had a feeling that this astrophysics business was more about number-crunching and less about stargazing than that Brian Cox fella would lead you to believe! Turns out, I was absolutely right! Within roughly an hour of getting introduced to my desk (replete with temperamental computer and ominous telephone) I was getting down to some serious spreadsheeting. Now, you may think that you have experience with spreadsheets, that the few IT lessons you spent learning how to divide a cell by another cell were hard work. When you have a spreadsheet that is 500 rows long and 20 columns wide, however, the story is somewhat different!

This was an astrological database, created for me by my supervisor Ben, showing various groups of objects that might be linked together, their movements in the heavens and their magnitudes of brightness. My first task was to sort out the objects that seemed to be moving similarly to one another, as this would mean that they were (hopefully) in some sort of binary arrangement. If two objects are close together and moving at roughly the same rate (This is measured by a process called Proper Motion*) and in the same direction then chances are they’re a binary! Whether or not one or more of the objects is a Brown Dwarf comes later on in our calculations.

Now, all this talk of databases and celestial motion is probably making some of you weak at the knees, and I don’t blame you one bit! Some of the calculations were pains in the backside, but luckily for me, I traded in people skills for number skills a long time ago, and set about squaring this, subtracting that, and performing a logic calculation based on the suitability of the other. Pretty soon we had a nice list of stellar objects that we could begin investigating further.

Wednesday

We’ve now begun to use images collected from the SDSS (Sloan Digital Sky Survey) and the UKIDSS (UK Infra-red Deep Sky Survey) surveys to actually try and see some of the objects behind the numbers. At first, trying to orientate yourself using these pictures is difficult, which is annoying when you’re trying to find where the two objects are in relation to each other, but nevertheless I’m pressing on and trying to pick up the knack. Sometimes this is made especially difficult with the UKIDSS pictures, because, although they show the objects we are looking for more clearly, the orientation is often different for each picture! This basically means that in one picture north is up, but east is left, and in another picture north is down and east is still left! Needless to say this is really confusing, but once you’ve finished tilting your head to the side you can pretty much understand where you are.

That’s pretty much it for the moment, but I’m sure I’ll have a whole smorgasbord of astro-facts next week! Mine’s a brown dwarf with a slice of lemon, Chin-chin!

Harry Saban – The Octave Doctor

*Proper Motion: This is used to describe the movement of a celestial object, relative to the center of the solar system, using a sort of co-ordinates system. The co-ordinates work like this:

File:Ra and dec on celestial sphere.png(Image from Wikimedia Commons)

Right Ascension (RA) is like longitude but for space, as if we were looking from the center of a sphere to its inner surface. Unlike normal co-ordinates it increases from right to left and has no negative values.

Declination (Dec) is basically the angle from the equator, and goes from +90 (North Pole) to -90 (South Pole).

Both of these values are generally measured in Arc-Seconds (1/3600 of a degree), Arc-Minutes (1/60 of a degree) or Degrees (1/1 of a degree).

The speed of light, and more precisely near the speed of light travel, has always fascinated me, but thinking about it raises the very interesting question, what happens if you actually get to, or near, the speed of light?

If we put aside the problems of getting an object up to that speed and simply imagine a bowler throwing a baseball and it spontaneously accelerating up to 0.9c, we only need to follow basic physics to predict what will happen.

A very simple answer to the above question is a lot of things, none of which are very nice, and none of which end well for the batter (or anyone nearby for that matter). At this speed (0.9c for those with a bad memory) everything else is practically stationary, the batter is stationary, the bowler is stationary, the spectators and fielders too, even the air molecules are stationary. Air molecules vibrate about at a rather pedestrian few hundred meters per second, where as the ball is moving at a few hundred million meters per second (269,813,21,.2 m/s to be precise). This means, as far as this thought experiment is concerned, that they are stationary. As a result, the laws of aerodynamics don’t apply here, the air molecules have no time to be forced out of the way and simply smack into the ball. This happens with such force that the oxygen and nitrogen in the air actually fuse with the carbon, hydrogen and oxygen in the ball. Each collision releases a huge burst of gamma rays, x-rays and other forms of energy, including light and heat.

This EM radiation expands outwards in a bubble centred on the pitcher’s mound, ionising any air molecules it meets, creating a shockwave of superheated plasma, approaching the batter at nearly the speed of light, only just ahead of the ball itself.

This fusion continues to occur on the leading edge of the ball as it moves through the air, slowing it down, similar to a rocket flying tail first while firing its rockets. However, the force of the on-going thermonuclear fusion is insufficient to even barely slow the ball. It does however begin to vaporise the surface, throwing out debris and particles at speeds close to the speed of light, this causes two or three more rounds of fusion as it hits the ionised air around it.

After around 70 nanoseconds the ball reaches the batter. The batter hasn’t even seen the ball leave the bowlers hand as the light carrying this information reaches the batter only 0.6 nanoseconds ahead of the ball. Collisions with the almost stationary air molecules has eaten the ball away to a slug of hot, ionised, expanding plasma, smashing into the air and creating even more fusion as it goes. The x-ray front of the plasma wave reaches the batter first; the disintegrating ball reaches the batter a split second later.

When the shockwave and what’s left of the ball eventually reaches the batter it’s still moving at a fair old lick, still reasonably close to the 0.9c it left the now vaporised bowler at. This shockwave scoops up and carries the batter, backstop and catcher all back through the stadium wall, as they and the wall begin to disintegrate. The shock wave of high energy EM waves and super-heated plasma continues to expand, and within the first 3 microseconds it has consumed the two teams, the stadium the car park and the surrounding half a mile of neighbourhood.

From an observers point of view on a distant hill, the first thing they would notice is a blinding flash of light, outshining the sun for several seconds and then, as it fades, a growing fireball rising into a mushroom cloud. The surrounding one and a half miles of city would be charred to a crisp and completely flattened, and a further two miles would have superficial damage, such as blown out windows and damaged roofs.

By an object, in this case a baseball, traveling at only 90% the speed of light, a nuclear explosion, somewhere in the region of about 1 kiloton has occurred, destroying a sizable chunk of populous city. Now this may seem an unlikely scenario, but it raises the interesting question, what if it did happen? In a future of faster and faster travel, we may have to severely limit the places where we can travel incredible speeds, or face the consequences…

N.B. A careful reading of the major league baseball rules implies that this would be a foul ball and the batter would be permitted to advance to first base, at least, where first base used to be

References:

http://nuclearweaponarchive.org/Uk/UKArsenalDev.html

http://en.wikipedia.org/wiki/Yellow_Sun

http://en.wikipedia.org/wiki/Nuclear_weapon_design

Two A-level physics books and my trusty calculator for most of the numbers

Pictures from:

http://what-if.xkcd.com

Alex Davis

Black holes. One of the universe’s most destructive forces, capable of tearing stars and planets to sheds, and swallowing them whole. Yet, scientists believe they could actually be the key to shaping the many millions of galaxies in the universe, creating and holding life itself. But moreover, scientists believe black holes could finally answer mankind’s most potent question: What came before the Big Bang?

 

The problem is, researching black holes is near impossible. By definition they are invisible, and current theories that seem to be able to explain everything else in the universe, collapse when applied to black holes.

 

We know black holes form when the most massive stars reach the end of their life. Red giants explode into a supernova, before finally violently collapsing into a point, creating the black hole. The reason something so small can have such a great gravitational field that not even light can escape, is due to the effect of mass bending space, shown by Einstein’s famous Theory of Relativity. The more massive an object, the more it bends space, like putting a heavy ball onto a trampoline. When this mass concentrates into a small area, the distortion and bending of space greatly increases. As black holes are so small and yet have such large masses, the distortion of space is phenomenal, giving it the quality of the event horizon. Beyond this point, space has bent so much, and the gravitational pull is so large, nothing can escape. A common analogy used by scientists is a waterfall. The closer water is to the drop off point, the faster the current. Once the water flows faster than you can swim, there is no way you’ll ever escape plunging to the bottom, representing the inescapable event horizon of the black hole.

 

But how can this possibly help scientists find out what came before the beginning of time? Well, it’s all down to the similarities of the black hole, and the big bang theory. According to the accepted current theory, the universe has been expanding for millions of years, and will continue to do so, but this expansion had to start somewhere. The theory states that expansion started from a single point in the universe. A singularity.

 

The difficulty is that the singularity, the very centre of the black hole, is where physics breaks down completely. It just doesn’t work anymore. Einstein’s Theory of General Relativity perfectly explains the massive, such as the stars and space, but when you put an incredibly large mass into such a small object, something strange happens. According to the theory, the singularity takes up exactly no space at all, and when implemented into the maths of general relativity, we get the answer physicists fear most. Infinity. This would mean that at the centre of a black hole, gravity is infinite, time stops, and physics collapses. The singularity is when our understanding of nature breaks down. So clearly there is a fundamental flaw in physics? Einstein knew of this flaw, but hoped such an object would never actually form, and even wrote a convincing paper proving this. At the time it was reasonable, but in the 1970’s pictures showed thick dense clouds of x-rays which quickly disappeared, giving convincing evidence of what we now know as the black hole.

 

But general relativity is very good at describing the very large, so to describe the singularity, quantum mechanics was used, which deals with atomic and sub atomic scale objects. But this is not as simple as it seems. Because quantum mechanics describes the minute, it can’t and doesn’t describe gravity, as it makes a negligible effect on atoms. This would normally be irrelevant, but when describing the singularity where gravity is phenomenally strong, the two theories just don’t mix.

 

To overcome this problem, theorists attempted to extend quantum mechanics to describe gravity, known as Quantum Gravity to try and link the famously incompatible General Relativity and Quantum Mechanics. But when inserted into the equations, again the result came up as infinity. In fact, it resulted in an infinite amount of infinities. Quantum Gravity had fallen apart. The theories were completely incompatible. This told scientists that at best, the theories were just an approximation of the universe. It meant the collapse of all physics as we know it.

 

Getting quantum mechanics and general relativity to work together has been the biggest challenge for physicists. Finding something to link them, or even finding new theories entirely to explain everything as a whole has been, and still is the current goal of theorists. Although it appears black holes have messed everything up, they represent a marvellous opportunity for physics. If the universe is expanding, then it must once have been more compact. A singularity.

 

So, if scientists can discover what is happening at the singularity in the black hole, this could help hugely in understanding and unlocking the secrets of what came before the Big Bang. Unfortunately with our current technology, we have only just been able to detect a possible black hole, let alone discover what happens inside one, and even these findings are still not 100% certain. For now, it’s all a big puzzle for the theorists, using clever maths and wondrous ideas to determine what might actually happen at the singularity, and until we can physically research black holes, we can never know for sure. There is hope yet though. Due to the impossible bending of space by a black hole, outside the event horizon, light from stars around the black hole is warped and reflected to produce a ‘halo’, a ring of light surrounding the event horizon. This would be possible to see, so discovering and observing a definite black hole for the first time is possible. Until then, we can only imagine one day, being able to answer the question: ‘What was there, before the Big Bang?’

 

Sources:

BBC Horizon, ‘Who’s Afraid Of A Big Black Hole?’

By Will Slack