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What is Special Relativity?

Michael Anissimov
Updated May 17, 2024
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Special relativity is a scientific theory describing how matter moves through time and space. When it was first published in 1905 by Albert Einstein, special relativity caused a revolution in the physics community, and made us look at the universe in a new light. Special relativity is one of the most well-confirmed physics theories of all time, and its predictions have been verified to more than twenty decimal places of accuracy.

The two basic postulates of special relativity are that the laws of physics are the same regardless of absolute velocity, and that the speed of light is constant for all observers. If you are in a closed box moving at constant velocity, special relativity predicts that no experiment you do inside the box can tell you how fast the box is moving. Likewise, the speed of light will remain the same for an observer inside the box, even if the box itself is moving at a large fraction of the speed of light.

Special relativity abandons the notions of “absolute space” and “absolute time” developed by Newton. Under special relativity, there is no such thing as a single universal time; rather, time is different for every observer. There is also no single universal measure of space; a single ruler can be longer or shorter depending on who measures it. Finally, special relativity unifies the concepts of space and time into a single four-dimensional structure called “spacetime.”

According to special relativity, if an object is moving at high speed relative to you, the object will appear to behave strangely. Its mass will increase, so that it becomes harder and harder to accelerate as it approaches the speed of light. It will appear to shrink in its direction of motion, becoming more and more distorted as it travels faster. The object's time will also become distorted; if there is a clock on the object, it will appear to tick more slowly. These effects happen to every object, but they only become noticeable once objects approach the speed of light.

Special relativity prohibits any object from traveling faster than the speed of light. If an object appears to go faster than lightspeed for one observer, it must be possible to find an observer who sees the object traveling backward in time. As an object's velocity approaches that of light, its mass and kinetic energy go to infinity. Even information may not travel faster than light, as this would allow messages to be sent backward in time as well.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.

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Discussion Comments
By anon1001248 — On Apr 03, 2019

It is possible to travel trillions of times faster than the speed of light and it is quite simple. The real problem is not in the achieving of that, but, is in the ensuring that the course of travel is clear of obstacles. So, just like submarines in the ocean, you have to make sure your course is clear. Since your craft is going faster than light speed, sensing the path ahead with e-m energy would not work. So traveling to the stars will be very possible but plotting and marking the safe corridors is what will take time. United States military black projects have already achieved this; if China and Russia have not yet, they need to become close economic and military allies of the U.S. or the developing world will swallow them whole. Happy trails.

By anon990091 — On Apr 06, 2015

It's much easier to understand Special Relativity if you just figure it out for yourself.

By anon334863 — On May 16, 2013

Everyone assumes nothing travels faster than the speed of light. If something did, do you think you'd be able to see it? My point is that just because Einstein's theory suggests faster than light speed is impossible doesn't mean it is impossible. If Einstein were a young man today, picking up where his old self left off, he'd be the first one to give the light speed limit its proper context.

By anon331081 — On Apr 20, 2013

Can you visualize going faster than the speed of light without violating Einstein's theory? It's not difficult if you understand the nature of e-m energy, mass physics, and normal space. Special Relativity is only a limit if you allow it to be. Open your mind!

By anon152304 — On Feb 13, 2011

Can effect give rise to its cause? If not, then all else must follow as a matter of consequence.

By anon128530 — On Nov 19, 2010

Einstein is 100 percent correct. There is no speed faster than light, if so then theoretically time travel would be possible (if you go fast enough, you would be going backward). We can reach close to the speed of light but we will never get there.

By anon127076 — On Nov 15, 2010

I think that Einstein's Special Relativity must correct the light velocity which is constant. Because if space and time change, then Light velocity also changes. We must find that the light velocity: c=300,000km/s is different from the light velocity: c'=300,000 km'/s'. (of which km, km' are denoted by space and s, s' are denoted by time) --Le

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated WiseGeek contributor and brings his expertise in paleontology, physics, biology,...
Learn more
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