Gold is a heavy element, so the inner electrons move fast enough that the relativistic mass increase and the length contraction are significant, according to (opens in new tab) a statement (opens in new tab) from Heidelberg University in Germany. However, most visible light gets reflected. Most metals are shiny because the electrons in the atoms jump from different energy levels, or "orbitals." Some photons that hit the metal get absorbed and reemitted, though at a longer wavelength. (Image credit: Jonathan Knowles via Getty Images) 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, according to Physics Central. Add in the effects of gravity, and the time dilation effect goes up to about 7 microseconds (millionths of a second). Because each satellite is 12,600 miles (20,300 kilometers) above Earth and moves at about 6,000 mph (10,000 km/h), there's a relativistic time dilation that tacks on about 4 microseconds each day. To get that pinpoint accuracy, the satellites use clocks that are accurate to a few nanoseconds (billionths of a second). These stations (and the GPS technology in a car or smartphone) are all experiencing higher accelerations due to gravity than the satellites in orbit.
The satellites are also sending signals to ground stations on Earth. This is because even though satellites aren't moving anywhere close to the speed of light, they are still going pretty fast. (Image credit: BlackJack3D via Getty Images)įor your car's GPS navigation to function as accurately as it does, satellites have to consider relativistic effects, according to PhysicsCentral (opens in new tab). GPS navigation is a great example of a relativistic time dilation. Meanwhile, the protons in the first wire are creating a net positive charge, and opposite charges attract. Because like charges repel, the two wires also repel.Ĭurrents in the opposite directions result in attraction, because compared to the first wire, the electrons in the other wire are more crowded, thus creating a net negative charge, according to the University of Illinois at Urbana-Champaign (opens in new tab). Because of the relativistic length contraction, they appear to be more closely spaced, so there's more positive charge than negative charge per length of wire.
(This assumes the currents are about the same strength.) Meanwhile, the protons in both wires are moving in comparison to the electrons in both wires. But if you put another wire with a direct current next to it, the wires attract or repel each other, depending on the direction in which the current is moving, according to physicists at the University of Illinois at Urbana-Champaign (opens in new tab).Īssuming the currents are moving in the same direction, the electrons in the second wire are motionless compared to the electrons in the first wire. Ordinarily, the wire would seem electrically neutral, with no net positive or negative charge, because the wire has about the same number of protons (positive charges) and electrons (negative charges). When a direct current of electric charge flows through a wire, electrons drift through the material. "Since this is the core principle behind transformers and electric generators, anyone who uses electricity is experiencing the effects of relativity," Moore told Live Science.Įlectromagnets work via relativity as well. Thomas Moore, a professor of physics at Pomona College in Claremont, California, uses the principle of relativity to demonstrate Faraday's law, which states that a changing magnetic field creates an electric current. This shows that there is no privileged frame of reference. 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.
The charged particles in the wire are affected by the changing magnetic field, which forces some of them to move and creates the current.īut now, picture the wire at rest and imagine the magnet is moving. If you take a loop of wire and move it through a magnetic field, you generate an electric current. Magnetism is a relativistic effect, and you can see this demonstrated via generators. (Image credit: Monty Rakusen via Getty Images) Close up of a worker holding an electromagnetic coil in an electromagnetics factory.
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