8 ways you can see einstein's theory of relativity in real life

11/29/2014 8 Ways You Can See Einstein's Theory of Relativity in Real Life

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8 Ways You Can See Einstein's Theory of Relativityin Real Lifeby Jesse Emspak, Live Science Contributor | November 26, 2014 11:55am ET

Relativity is one of the most famous scientific theories of the 20thcentury, but how well does it explain the things we see in our dailylives?

Formulated by Albert Einstein in 1905, the theory of relativity is thenotion that the laws of physics are the same everywhere. The theoryexplains the behavior of objects in space and time, and it can be usedto predict everything from the existence of black holes, to lightbending due to gravity, to the behavior of the planet Mercury in itsorbit.

The theory is deceptively simple. First, there is no "absolute" frame ofreference. Every time you measure an object's velocity, or itsmomentum, or how it experiences time, it's always in relation tosomething else. Second, the speed of light is the same no matter who

measures it or how fast the person measuring it is going. Third, nothing can go faster than light. [Twisted Physics:7 Mind-Blowing Findings]

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The implications of Einstein's most famous theory are profound. If the speed of light is always the same, it meansthat an astronaut going very fast relative to the Earth will measure the seconds ticking by slower than anEarthbound observer will time essentially slows down for the astronaut, a phenomenon called time dilation.

Any object in a big gravity field is accelerating, so it will also experience time dilation. Meanwhile, the astronaut'sspaceship will experience length contraction, which means that if you took a picture of the spacecraft as it flew by,it would look as though it were "squished" in the direction of motion. To the astronaut on board, however, allwould seem normal. In addition, the mass of the spaceship would appear to increase from the point of view ofpeople on Earth.

But you don't necessarily need a spaceship zooming at near the speed of light to see relativistic effects. In fact,there are several instances of relativity that we can see in our daily lives, and even technologies we use today thatdemonstrate that Einstein was right. Here are some ways we see relativity in action.

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1. Global Positioning System

In order for your car's GPS navigation to function as accurately as it does, satellites have to take relativistic effectsinto account. This is because even though satellites aren't moving at anything close to the speed of light, they arestill going pretty fast. The satellites are also sending signals to ground stations on Earth. These stations (and theGPS unit in your car) are all experiencing higher accelerations due to gravity than the satellites in orbit.

To get that pinpoint accuracy, the satellites use clocks that are accurate to a few billionths of a second(nanoseconds). Since each satellite is 12,600 miles (20,300 kilometers) above Earth and moves at about 6,000miles per hour (10,000 km/h), there's a relativistic time dilation that tacks on about 4 microseconds each day. Addin the effects of gravity and the figure goes up to about 7 microseconds. That's 7,000 nanoseconds.

The difference is very real: if no relativistic effects were accounted for, a GPS unit that tells you it's a half mile(0.8 km) to the next gas station would be 5 miles (8 km) off after only one day. [Top 10 Inventions that Changedthe World]

2. Electromagnets

Magnetism is a relativistic effect, and if you use electricity you can thank relativity for the fact that generatorswork at all.

If you take a loop of wire and move it through a magnetic field, you generate an electric current. The chargedparticles in the wire are affected by the changing magnetic field, which forces some of them to move and createsthe current.



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But now, picture the wire at rest and imagine the magnet is moving. In this case, the charged particles in the wire(the electrons and protons) aren't moving anymore, so the magnetic field shouldn't be affecting them. But it does,and a current still flows. This shows that there is no privileged frame of reference.

Thomas Moore, a professor of physics at Pomona College in Claremont, California, uses the principle of relativityto demonstrate why Faraday's Law, which states that a changing magnetic field creates an electric current, is true.

"Since this is the core principle behind transformers and electric generators, anyone who uses electricity isexperiencing the effects of relativity," Moore said.

Electromagnets work via relativity as well. When a direct current (DC) of electric charge flows through a wire,electrons are drifting through the material. Ordinarily the wire would seem electrically neutral, with no netpositive or negative charge. That's a consequence of having about the same number of protons (positive charges)and electrons (negative charges). But, if you put another wire next to it with a DC current, the wires attract or repeleach other, depending on which direction the current is moving. [9 Cool Facts About Magnets]

Assuming the currents are moving in the same direction, the electrons in the first wire see the electrons in thesecond wire as motionless. (This assumes the currents are about the same strength). Meanwhile, from theelectrons' perspective, the protons in both wires look like they are moving. Because of the relativistic lengthcontraction, they appear to be more closely spaced, so there's more positive charge per length of wire thannegative charge. Since like charges repel, the two wires also repel.

Currents in the opposite directions result in attraction, because from the first wire's point of view, the electrons inthe other wire are more crowded together, creating a net negative charge. Meanwhile, the protons in the first wireare creating a net positive charge, and opposite charges attract.

3. Gold's Yellow Color

Most metals are shiny because the electrons in the atoms jump from different energy levels, or "orbitals." Somephotons that hit the metal get absorbed and re-emitted, though at a longer wavelength. Most visible light, though,just gets reflected.

Gold is a heavy atom, so the inner electrons are moving fast enough that the relativistic mass increase issignificant, as well as the length contraction. As a result, the electrons are spinning around the nucleus in shorterpaths, with more momentum. Electrons in the inner orbitals carry energy that is closer to the energy of outerelectrons, and the wavelengths that get absorbed and reflected are longer. [Sinister Sparkle Gallery: 13 Mysterious& Cursed Gemstones]

Longer wavelengths of light mean that some of the visible light that would usually just be reflected gets absorbed,and that light is in the blue end of the spectrum. White light is a mix of all the colors of the rainbow, but in gold'scase, when light gets absorbed and re-emitted the wavelengths are usually longer. That means the mix of lightwaves we see tends to have less blue and violet in it. This makes gold appear yellowish in color since yellow,orange and red light is a longer wavelength than blue.

4. Gold Doesn't Corrode Easily

The relativistic effect on gold's electrons is also one reason that the metal doesn't corrode or react with anythingelse easily.



Gold Nuggets

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Gold has only one electron in its outer shell, but it still is not as reactive as calcium or lithium. Instead, theelectrons in gold, being "heavier" than they should be, are all held closer to the atomic nucleus. This means thatthe outermost electron isn't likely to be in a place where it can react with anything at all it's just as likely to beamong its fellow electrons that are close to the nucleus.

5. Mercury Is a Liquid

Similar to gold, mercury is also a heavy atom, with electrons held close to the nucleus because of their speed andconsequent mass increase. With mercury, the bonds between its atoms are weak, so mercury melts at lowertemperatures and is typically a liquid when we see it.

6. Your Old TV

Just a few years ago most televisions and monitors had cathode ray tube screens. A cathode ray tube works byfiring electrons at a phosphor surface with a big magnet. Each electron makes a lighted pixel when it hits the backof the screen. The electrons fired out to make the picture move at up to 30 percent the speed of light. Relativisticeffects are noticeable, and when manufacturers shaped the magnets, they had to take those effects into account.

7. Light

If Isaac Newton had been right in assuming that there is an absolute rest frame, we would have to come up with a



Liquid Mercury

Credit: MarcelClemens | Shutterstock.comView full size image

Credit: Andrii Malysh |Shutterstock.com


different explanation for light, because it wouldn't happen at all.

"Not only would magnetism not exist but light would also not exist, because relativity requires that changes in anelectromagnetic field move at a finite speed instead of instantaneously," Moore, of Pomona College, said. "Ifrelativity did not enforce this requirement changes in electric fields would be communicated instantaneously instead of through electromagnetic waves, and both magnetism and light would be unnecessary."

8. Nuclear Plants and Supernovas

Relativity is one reason that mass and energy can be converted into each other, which is how nuclear power plantswork, and why the sun shines. Another important effect is in supernova explosions, which signal the death ofmassive stars.

"[Supernovas] exist because relativistic effects overcome quantum effects in the core of a sufficiently massive



Supernova Remnant W49B

Credit: Caltech/SSC/J. Rho and T. Jarrett and NASA/CXC/SSC/J. Keohane et al.View full size image

Supernova remnant W498. This view combines infrared images from the ground (red, green) withX-ray data from NASA's Chandra X-Ray Observatory (blue).

star, allowing it to suddenly collapse under its own weight until it becomes a much smaller and harder neutronstar," Moore said.

In a supernova, the outer layers of a star collapse down onto the core, and create a gigantic explosion that, amongother things, creates elements heavier than iron. In fact, nearly all the heavy elements we are familiar with aremade in supernovas.

"We are made of stuff created in and dispersed by [supernovas]," Moore said. "If relativity did not exist, even themost massive stars would end their lives as white dwarfs, never exploding, and we would not be around to thinkabout it."

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Jesse Emspak

Jesse Emspak is a contributing writer for Live Science, Space.com and Toms Guide. He focuses on physics,human health and general science. Jesse has a Master of Arts from the University of California, Berkeley Schoolof Journalism, and a Bachelor of Arts from the University of Rochester. Jesse spent years covering finance and cuthis teeth at local newspapers, working local politics and police beats. Jesse likes to stay active and holds a thirddegree black belt in Karate, which just means he now knows how much he has to learn.Jesse Emspak on

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