# Special Relativity in the Natural World

Instructor: Michael Blosser

Michael has a Masters in Physics and a Masters in International Development. He has over 5 years of teaching experience, teaching Physics, Math, and English classes.

This lesson will introduce special relativity and its effects in the natural world, using examples to demonstrate how important of a role special relativity plays in the everyday life of our world.

What if I told you that an astronaut who goes on a 5-year mission to another solar system would age more slowly than those of us on Earth? Or that the faster you go, the more your mass would increase? These are all concepts in the realm of special relativity, the famous theory that Einstein created in 1905. You may be thinking that these are cool concepts, but are so abstract that they have no relation to anything we can observe in our natural world. This lesson will show you that special relativity is not only a cool concept used for science fiction -- it also plays a big role in the everyday occurrences of our natural world.

## Special Relativity

Special relativity is the study of space and time and how they relate to each other depending on the motion of two objects in different inertial frames of reference. Albert Einstein created the theory of special relativity in 1905. Special relativity is different than general relativity: in special relativity the motion of the objects in relation to each other are uniform, meaning that the objects are either at rest or are moving at a constant velocity. This also means that the objects are not accelerating (speeding up or slowing down) and that these objects are not moving in a curve. Depending on the inertial frames of reference of two objects, we can observe the phenomena of length contraction and time dilation; this is covered in another lesson.

Einstein's theory of special relativity is based on two key theories::

• That every term of reference is relative, that is, in relation to something else. Therefore, the laws of physics don't change, no matter if an object is in motion or in an inertial frame of reference (at rest or constant velocity).
• That the speed of light is constant -- always the same -- and that nothing can go faster than the speed of light.

## Special Relativity in our Natural World

### Electricity

Did you know that electricity had anything to do with special relativity? Magnetism relies on a relativistic effect. It works because there is no absolute frame of reference, as indicated by Einstein's first principle of relativity. Electromagnets only affect charged objects if they are moving. As the charged object moves in relation to the reference frame of the electromagnet, it starts to feel the effect of the length contractions (a phenomenon of special relativity) of its moving electrons, causing the object to be attracted or repelled by the electromagnet.

### GPS

GPS is a tool that has become essential in our everyday lives. Virtually every smartphone uses GPS, or Global Positioning Systems, to track our movements and help us with directions. Since our phones are being sent a signal from satellites thousands of feet above us moving at velocities of thousands of miles per hour, time dilation needs to be taken into account or our GPS would get us lost fairly quickly.

### The Color of Gold

You may not have known this, but the yellowish color of gold is directly caused by relativistic effects! Gold is a heavy atom with 79 electrons and 79 protons. The inner electrons are moving so fast around the nucleus of the atom that they move at roughly half the speed of light. This velocity causes the special relativity effects of length contraction and mass increase. These relativistic effects change the electron orbitals and cause more blue light to be absorbed. Therefore the light that bounces off of gold has less blue in it. Because yellow is complementary to blue, the light that we see reflected off of gold appears more yellowish. This phenomenon produces the color we know as gold.

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