Illuminating Reality

The average sci-fi fan likely takes for granted the speed of light and no doubt breaking the speed limit so callously is an expected aspect of story telling, but there are some really interesting implications to traveling at relativistic speed that I don’t think a whole lot of people are aware of. A fairly simple implication is, from our point of view, that an object approaching us at or near the speed of light (ie relativistic speed) appears as tinted blue. A more complicated implication is that time is running slower for the relativistic passenger. Let me explain…

Let’s say there’s a guy riding a motorcycle near the speed of light.  Because light acts like a wave, the motion of the object is going to compress and stretch the light waves radiating from it.  This is known as the Doppler Effect and is evident every time you pass a blaring siren – you hear the pitch rise as you approach it and then drop off as you move away from it – “yyyyyeeeeaaaarrrrooooowww!”  This is simply because the sound waves are being compressed as you approach it; this shortens the wavelength and creates a higher frequency sound.  Naturally, as it recedes, the sound drops in pitch because the waves are stretched to lower frequencies.

This is really a property of all waves, including light.  In fact, it’s happening all around us but the amount of shift in the light spectrum is so tiny that we just can’t detect it.  However taking our scenario above, the speed of the motorcycle rider would significantly amplify the shift and he would appear to turn blue as he approached you and red as he passed you.  Incidentally, this Doppler Shift is used by astronomers to detect planets orbiting other stars (among other things).

Another interesting implication of traveling at relativistic speed is that time slows down for the traveler in relation to the observer.  This is known as Time Dilation and is a result of time being relative from observer to observer as described by Einstein’s Theory of Relativity.  In the case of our motorcycle rider, because of his speed his watch appears to run slower to the people observing him.  This is a strange property of the Universe but we observe it in many places.  One of the best examples is muon decay from cosmic rays colliding with our upper atmosphere.

Cosmic Rays are high energy particles formed in powerful celestial events such as the cores of stars, supernovae, neutron stars and black holes.  They blast out in every direction in the cosmos and daily they smack into our atmosphere.*  When these protons collide with air molecules they break apart into sub-atomic particles that decay very quickly.  One of these types of sub-atomic particles is the Muon, something very similar to the Electron yet significantly more massive and highly unstable.  Muons created in these collisions live for one to two microseconds or 1.0 × 10^-6 seconds.  That’s a ridiculously short time so it would be expected that we can only detect these muons in the upper atmosphere because there aren’t around long enough to make it to the surface – even traveling at the speed of light.  Yet they reach muon detectors on the surface daily!  What gives?

The reason is because of Time Dilation, pure and simple.  The one to two microseconds the muon experience appear to be longer to us, the observer.  In other words, time for the muon runs slower from our point of view.  To explain why is a bit involved, but the video below does a good job.  In a nutshell, relativity is allows for time to be flexible to keep the speed of light a constant for everyone.

* it should be noted that these collisions are at MUCH higher energies than that produced by the LHC, and because the Earth is still here it’s safe to assume that the LHC can’t produce an Earth devouring black hole – otherwise it would have already happened.

One of my hobbies that’s a carry-over from my years as a soldier in the Army is long range shooting.  Understanding and exploiting the science of ballistics lets me take a particular load of ammunition and compute a predicted trajectory based on environmental factors such as barometric pressure, altitude and wind.  But there’s also an art form to creating a stable shooting platform with your body, controlling your breathing and making the shooting process fluid, not to mention estimating the wind speed and direction downrange.

Here’s a clip from a recent shoot out in the desert.  The targets are 10×17″ AR500 steel targets – about the size of a laptop screen.

Update:  I just came back from another trip out to the same area and this time made a few hits on the steel targets at a whopping 1750 yards.  Time of flight to the target was almost 2 seconds and it was another 3 seconds before we heard the report.

Did you know that gravity is a bit of a mystery to scientists?  Given that we have space probes orbiting Saturn and Mars right now, you’d think it would be well understood, but the reality is it’s the most mysterious of the Four Fundamental Forces of Nature.   Mathematically it’s well understood and can be calculated with great precision, yet it’s so weak compared to the other forces, all of which are roughly comparable to each other.  How weak? Try – 10⁴⁰ weaker than the electromagnetic force, in other words:

0.00000000000000000000000000000000000000001 times as strong

Don’t believe me? Ever notice that you can pick up a paper clip with a refrigerator magnet, which is pretty weak, with relative ease?  The gravity from the entire mass of the Earth is being defeated by that little magnet, which seems so unintuitive and bizarre, doesn’t it?

The Four Fundamental Forces of Nature, according to the Standard Model, are Electromagnetism,  Strong Nuclear Force, Weak Nuclear Force and Gravity.  This isn’t speculation either – the Standard Model is one of the greatest achievements in Science, forming the backbone of modern physics and it works exceptionally well.

These forces interact with matter via carrier particles (aka bosons) and have a finite range to their interaction – except gravity.  To this day there is no known force carrier particle for gravity (they’ve been theoretically dubbed “gravitons”); it can’t be absorbed or shielded like the other forces; it has an unlimited range and it’s behavior is always attractive in nature; it’s somehow tied to the mass of objects in that it interacts with every particle that has mass.

Understanding gravity has been a long and storied endeavor, but it was Sir Issac Newton who made the first significant breakthrough when he published his Principa Mathematica in the 17th Century, wherein he described his universal law of gravitation.  His simple equation was highly accurate at calculating the motion of everything from objects falling out of a tree to the orbit of planets.  His work survived for two hundred years as the dominant theory of gravity until Einstein came along in 1905 and fundamentally changed the way we think of gravity.

Part of the problem was that there was no known mechanism for gravity.  It’s effects could be calculated, but it wasn’t clear how, for example, the Sun reach out to the Earth, across 93 million miles of empty space and tugged on it.  Einstein wondered if the Sun disappeared, how would the Earth know?  In other words, how did the force actually work to travel that distance?  Part of the problem it turns out was that we were thinking of Gravity in the same way we thought of the other known force at the time: electromagnetism.  Einstein radically overturned Newton by defining gravity not as a typical force but as curvature of space itself.  When Einstein published his Theory of Relativity ushered in a new age of physics, solving many of the outstanding problems of Newton’s theory – mainly that because gravity distorts space, the Sun reaches out to the Earth through that distortion to pull the Earth inward.

Einstein’s theory was confirmed  in many areas such as resolving the long standing anomaly with Mercury’s orbit that Newton’s theory couldn’t account for as well as the observed phenomenon of light being refracted by the mass of the Sun during a total eclipse.  Like any good theory, Einstein’s work makes lots of testable predictions that have been observed over the years, but around the same time he was getting lots of attention in the world, the world of atoms was slowly being revealed and it required a new kind of physics to describe.

Quantum Mechanics is to sub-atomic particles what General Relativity is to the orbit of planets.  It’s the physics that accurately models the way atoms and sub-atomic particles interact and has been tested to a high degree of accuracy as well.  There is a really big problem though: Quantum Mechanics does not jibe well with General Relativity.  Physicists tried using Einstein’s equations to model the interactions of molecules and atoms to find that as you get down to those very small scales, everything starts to fall apart and you get gravitational values of infinity (psst, that’s a sign there’s a problem with your theory).

So General Relativity is shown repeatedly to be correct on large scales and Quantum Mechanics is shown to be accurate the same way at the sub-atomic scale – what gives?  Gravity is messing things up in a big way or should I say our incomplete understanding of gravity is messing things up.  Finding an accurate quantum-scale model of gravity has been an elusive quest for physicists.  Some of the ongoing attempts include Loop Quantum Gravity*and String Theory, both of which are so theoretical that they currently can’t be tested in the first place.

This is why the Large Hadron Collider (LHC)  is particularly exciting to physicists.  It’s hoped that when it’s operating at full power, the LHC will be able to expose the innards of the sub-atomic world at an energy scale never before witnessed.  This could be the very device that detects gravitons, the theoretical force carrier for gravity or the Higgs boson which is theorized to give particles mass (remember, gravity is related to mass).  Exciting stuff!

So gravity remains a mystery for now; something we understand well enough to calculate its behavior extremely accurately, but mysterious enough that its mechanism remains elusive.

* Read Lee Smolin’s “Three Roads to Quantum Gravity” for an introduction to the theory…have aspirin handy.

The Large Hadron Collider (LHC) at CERN successfully collided two proton beams yesterday!  Yes, we are still here – the Earth hasn’t been destroyed by a black hole or created a rift in the space/time continuum.  This has been a long time coming, especially after the setbacks of the last year – first with a superconducting magnet failure and more recently with a mischievous bird dropping pieces of baguette in vulnerable areas.

That picture over there is part of the detection display at the  CMS experiment (click the image to see the full display).   Where those green lines converge in the center is the point of collision.  The green lines shooting out are tracks of unstable, charged pions as they fly to the detector strips in the device (the yellow rectangles).  The red and blue boxes show where the energy was detected and that’s key to these experiments.  At higher and higher energies, particle collisions tend to reveal their “guts” in more detail and the LHC will be operating at the highest energies we’ve ever collided particles with.

Exciting times ahead!

If you’ve ever worn glasses, used a camera or burned ants with a magnifying glass – you’ve used a lens.  All a lens really does is refract light, warping its path and focusing it so that we’re able to see things a bit differently.  Telescopes focus light onto receptors that capture photons that have traveled across the Universe while eyeglasses are built specifically to match just the right amount of distortion necessary to give one “correct” vision.

These physical lenses work because they are made with specific materials in mind and shaped in such a way that they focus the light.  But there’s something else that can focus light: gravity.  Einstein showed us this almost a hundred years ago and a prediction of General Relativity is that sufficiently large masses should be able to act as a lens.  These Gravitational Lenses were sought after for decades but not discovered until 1979, yet have become a very important tool for astronomers.

A gravitational lens occurs when so much mass is located between an observer and a distant object, that the light from the object gets distorted and focused along the way to the observer.  This results in all kinds of weird things like repeating patterns such as Einstein’s Cross and warping arcs, but also it tends to allow astronomers to observe objects behind other objects or help to magnify extremely faint objects.

The photons from those distant objects have often traveled for billions of years across the expanding Universe and arrive on Earth in such few numbers, but when they travel through a gravitational lens they become focused and arrive more tightly packed.  And because the physics of gravitational lensing is well understood, astronomers can measure the lensing effect to determine the mass of the cluster bending the light.  This last bit has become very useful in hunting for the elusive “Dark Matter” that appears to make up a much larger quantity of the Universe than normal matter – but that is another story.

String Theory is one of the newest chapters in our attempt to develop a theoretical physics model of how the Universe works. It came about as the result of the incompatibility of General Relativity and Quantum Mechanics. Those two theories have proven exceptionally accurate but only within their domains. Einstein’s General Relativity supplanted Newton’s classical mechanics by describing space and time as an interwoven fabric that mass distorts and it has been proven over and over again to be correct, however when you start to apply it to the realm of the very small such as atoms and sub-atomic particles the theory completely falls apart. As early 20th Century scientists started to study atoms they discovered there was a new physics needed to describe their behavior – this lead to the development of Quantum Mechanics, which has also been shown to be exceptionally accurate at describing the tiny sub-atomic world, yet when you apply it to large scales it too falls apart. This incompatibility confounded physicists for several decades and the idea of a unified theory that worked on all scales seemed almost impossible.

Then String Theory came around as an attempt to try to merge the two together to a loose degree. The idea is rather elegant, describing the smallest sub-atomic bits as strings or loops of energy vibrating at different frequencies. These different frequencies describe different particles, so one type results in protons, the other in electrons, etc. Mathematically it solves lots of problems, but also creates a few bizarre ones. For example, for everything to resolve to describe the Universe we observe, String Theory suggests up to 11 higher dimensions – that’s quite a bit more than up-down, left-right, backward-forward(X, Y, Z) and time. But the biggest problem of all is that currently there is no way to test String Theory’s predictions and in science, being unable to do so is a non-starter. Nevertheless, many physicists are pouring their careers into making it all work, but if you thought Quantum Mechanics was difficult to wrap your anthropic brain around, check out this ultra-simplified description of String Theory in under two minutes. This video won a well deserved award in the scientific community…

So the Space Shuttle just passed over the LA Basin a little while ago, ripping through the air at high altitude, creating a sonic boom that shook windows and generally startled those who weren’t expecting it.  This is what happens in LA when the shuttle has to land at Edwards AFB out in the Mojave Desert, but it’s not like it’s zipping between buildings here.  The Shuttle comes in on final approach over the Pacific Ocean at a pretty steep angle; much more than an airliner starting its descent.  So by the time it is over downtown Los Angeles, it’s still at a pretty high altitude, at least 60,000 feet which is roughly twice as high as you fly when traveling across country on a 757.

But what causes the sonic boom that we hear and feel?

First we have to understand what sound is.  Sound needs a medium to travel (see my post about the Sound of the Big Bang) through (air in this case) and what we hear and feel is a compression of the air.  Sound is a wave that moves through the air, with long low frequency waves making low pitch sounds and tight high frequency waves making higher pitch sounds.  This is essentially how our speakers work – and in a vacuum you won’t hear anything.  But as an aircraft moves quickly through the air, it compresses the air flowing around it.  As it approaches the speed of sound, a shock wave is formed which acts like the wake from a boat moving through water.  This “wake” is a cone of very compressed air that travels out from the aircraft.

The faster the plane goes, the more compressed the cone and more compression means more pressure.  When the cone passes over us we get hit by a short blast of compressed air.  That’s the first part of the “boom” – a sudden change in pressure at our ears.  But because the plane is trailing a cone of compressed air, we get a second blast of slightly less compressed air.  This is why a sonic boom has a specific signature – a double boom.  Seismologists can track them and pick them out from earthquakes for this very reason.

Questions? Ask in the comments section…

Oh, one more thing, check out the sonic boom range pattern created over the area

Well geez, I wrote about why the sky is blue yesterday and now one of my favorite bloggers, Ethan Siegel, has written about why the sky is red at sunset and even better, why the moon appears to change color near the horizon.  Remember when you asked me about that one, Bev?

Check out Ethan’s blog for the details and rather easy to understand explanations…

Here’s one I don’t hear often enough:  Why is the sky blue?  It’s not as simple an answer as you might expect.  The air we breathe is a mixture of oxygen and nitrogen but it sure looks invisible to us when we wave our hands through it.  The clouds are white for the most part, but they’re made up of water vapor.  What gives?

One way to approach this mystery is to find correlations.  For example, take a look at this picture from high altitude:

What’s going on here? The sky is bluer closer to the surface but fades to black as it approaches space.  How does this correlate?  Well, we know that the density of the atmosphere is greatest near sea level and gradually drops off as you go up in altitude, so much so that even at 16,000 feet humans need to breathe an oxygen source or risk altitude sickness.  So is it the oxygen that is making the sky appear blue?  Yes and no.

What’s actually happening is the blue wavelength of light is being scattered in all directions more heavily than the other colors.  Light that we see is made up of a spectrum of colors (remember the color gradient from light passing through a prism?) determined by their frequency – short frequency goes towards blue and longer frequency towards red.  As light moves through the atmosphere it comes in contact with molecules in the air but the longer wavelengths tend to be unaffected while the shorter wavelengths get bounced around in all directions.  So while the rest of the colors head straight to us, the blue wavelengths shoot off in all directions like sparks from a sparkler thereby creating a flood of blue light no matter which direction you look upwards to.

That’s about the most simple answer I can give, but it’s nowhere near complete.  There are other complications such as how the cones and rods in our eyes bias towards blue and how the density of the atmosphere effects the scattering.  But for the most part, when someone asks you “why is the sky blue?” you can say with reasonable confidence “because the air scatters the blue portion in all directions.”

Hmm, this means I’ll have to bookend this discussion with “Why are Sunsets Red?” next time…

Ethan Siegel has an interesting write up on Starts with a Bang where he answers the question:  what did the big bang sound like?  This is an interesting question because, naturally people assume the Big Bang was an explosion in space and explosions make sound, right?  The reality is the Big Bang was an explosion OF space and time, but also we know quite well that sounds doesn’t travel in a vacuum and therefore you can’t hear anything in space.  Or can you?

To answer this question you first have to ask:  what is sound?  Sound comes from changes in pressure as a wave moves through a medium (air or water for example).  This is how speakers work; compressing or stretching the air around them by using magnets to distort and vibrate a surface.  The higher the frequency, the higher the pitch but the human ear can only hear a certain frequency range, so it would have to remain within that spectrum for us to hear it.

So we know space is nearly a vacuum so the density of the medium is almost non-existent and therefore impossible to travel through.  For us to be able to hear sound in space we’d need the vacuum of space to become significantly more dense, similar to the air we breathe.  This may sound impossible, but it isn’t when you consider that the Big Bang shows us that if we go back in time we find the matter in the Universe in a much, much more dense state.  Go back far enough and you start to approach the density of air on Earth – but all around you!  So yes, we could hear the Big Bang at this point, but there would be the small problem of space being almost a billion degrees Fahrenheit versus the near Absolute Zero it is now.

How loud would it be? Check out Ethan’s blog…