How fast does light travel through the air and the energy is lost?

It varies depending on the place of consumption.

Most substances do not significantly slow down the speed of light. However, in 1998, Harvard University's Lene Vestergaard Hau announced that she had reduced the speed of light to 17 meters per second. In 2001, she made the light stop completely.

Of course, her team was not working with ordinary materials, but with Bose-Einstein condensates.

This extraordinary substance consists of a cloud of atoms that cools to one millionth degree above absolute zero, forming the Bose Einstein condensate. It is essentially a single quantum object, a bit like a giant atom, in which all the atoms are in the same quantum state and move in the same way, as if they were one object.

The trick to slowing down the speed of light is to illuminate the Bose Einstein condensate with two beams of light that intersect perpendicularly. One of the beams carries information, called a detection light; The other beam is called coupled light. When coupled light hits a condensate, it becomes completely transparent, allowing the detection light to pass through.

There is an electron in the outermost orbital of the sodium atom, and probing the interaction between light and this electron is crucial to this process. When an atom absorbs a photon from the speed of detection light, the outer electrons jump to a higher energy level. After a short time, it fell back to its original energy level, releasing a photon.

Unfortunately, this process is completely random, so all the information in the original beam is lost.

The result is that the components of the detected light pulse at different frequencies pass through the condensate at different speeds, and the result is that an input pulse is clustered in a cloud of sodium atoms and passes slowly, during which the spin of the atoms is affected by the pulse. If the coupled light is withdrawn at this point, the light pulse (or at least the information in it) is bound to the atom's spin pattern, and the beam essentially stops. The coupling light lights up again, and the condensate re-emits a pulse of light.

Slowing down or stopping the pace of light may have practical applications in computing. Physicists have long wanted to build optical computers that use the speed of light instead of electrons to transmit signals and perform calculations. They also hope to build quantum computers that use the quantum states of atoms and bizarre quantum principles to build processors with supercomputing power.

HAU's tips for dealing with light may also help scientists simulate how light behaves near black holes. In fact, studying the speed of light is perhaps the best way to unravel the deepest mysteries of the universe – those that are determined by the help of the speed of light.

Translated from newscientist,

The reason why we can see the beautiful planets in the night sky and even the universe now is because we see the light produced by stars tens of millions of light-years away, for example, it takes 8 minutes for the sun's light to reach the earth, and if the sun suddenly disappears, then we will get the result after 8 minutes, how far does the light travel? We can't get a definite answer to this, because the most distant galaxy we have observed so far is 13.1 billion light-years, and we have seen the light it emitted 13.1 billion years ago, so will the propagation of light in the universe consume energy?

The propagation of light that we see so far is a phenomenon of Kepler's shift, when the galaxy is close to us showing red light, when the galaxy is far away from us showing blue light, we know that the universe is expanding through the observation of this phenomenon, according to the observation of the movement of nearby galaxies, we know that the expansion of the universe is constantly accelerating, light as a particle and a wave.

It's fundamentally what happens to him when it goes through an ever-expanding universe. The universe as a whole is constantly expanding, which means that the distance between many galaxies is increasing. As light moves away from galaxies, the universe expands, meaning that the distance light needs to travel is also increasing.

However, the astronomical standard of one trillion kilometers is still relatively small. A trillion kilometers is about one-tenth of a light-year. This distance is actually very small in the universe, and a more useful unit is the astronomical unit (AU), which measures the distance between the Earth and the Sun.

Trillion kilometers are about 10000au.

On the scale of our solar system, this would extend from the Sun to the Ultra Nebula. This distance is 40 times the distance from Pluto to the Sun and far beyond what we could have predicted. So will the light of our sun travel hundreds of billions of light years, the answer is no, it will be blocked, it will be swallowed by black holes, but if it does not encounter the above conditions, then it can propagate infinitely in the vacuum environment of the universe, without time and distance limitations.

When light travels in a vacuum, the energy makes no loss. Because there is no medium in midspace, it will not cause the loss of light energy. Light is a physical term whose essence is a stream of photons in a specific frequency band.

A light source emits light because the electrons in the light source gain extra energy. If the energy is not enough to make it jump to a more outer orbit, the electrons undergo an accelerated motion and release the energy in the form of a wave.

If the transition is followed by just enough to fill the vacancy in the orbit and from the excited state to the stable state, the electron stops transitioning. Otherwise, the electrons jump back to their previous orbits again and release energy in the form of waves.

The propagation of light in matter should be energy-intensive, because light is an electromagnetic wave, and the energy of light is stored in photons.

For example, if you let a beam of light shine through a layer of glass, you will not feel a decrease in light intensity, but when the light shines through a stack of glass, the decrease in light intensity will be obvious, which is the result of the decrease in photon energy.

Be. By the time light of thousands of light-years reaches Earth, the energy is already weak, so only special telescopes – astronomical telescopes – can receive it! The reason why it can be reached is because the initial intensity of these lights is very strong, and because most of the space outside the Earth is vacuum, the light is less weakened.

to be consumed; When a photon is reflected from a smooth glass, its amplitude decreases considerably, because one beam of light may become two beams of light; There will also be reflections in the air, although the phase and velocity will not change.

Sound propagation depends on the vibration of the medium and therefore requires energy consumption.

Light belongs to electromagnetic waves, propagation does not require a medium, in principle, light can travel far and wide, as long as nothing captures or absorbs photons, light can travel wirelessly and far.

The propagation of light in matter should be energy-intensive, because light is an electromagnetic wave with wave-particle duality, and the energy of light is stored in photons, and the mutual impact of the electrons and the medium during the relay will inevitably consume the energy of the photon, that is, the energy of light.

For example, if you pass a beam of light through a layer of glass, you will not feel a decrease in light intensity, but when the light shines through a stack of glass, the decrease in light intensity will be noticeable, which is the result of the decrease in photon energy.

It is bound to decay.

First of all, you have to understand that vacuum does not mean nothing, but that the particles in the vacuum are not excited. (Scientifically, there is no such thing as an absolute vacuum, and it is impossible for space to be free of any particles anyway).

The physical vacuum is actually a fluctuating sea of energy. When the energy reaches the peak, the energy is converted into a pair of positive and negative elementary particles, and when the energy reaches the trough, a pair of positive and negative elementary particles annihilate each other and are converted into energy.

Light has wave-particle duality, that is, a light can be seen as both a particle beam and a wave, and you should easily understand that a particle beam passes through a space full of particles (not excited), can it not be attenuated?

In addition, you should note that light barely transmits heat, and the heat of the sun is mainly diffused in the form of invisible light such as infrared rays, and in the process of diffusion, even if the sum of energy remains the same, the temperature will drop due to heat dispersion.

The pure energy of photons does not decay during movement (propagation).

Increasing the distance between the emitter and the old escort source can reduce the radiation damage cavity, not because the energy of the photons decreases (as mentioned above, it does not decrease), but because of two reasons:

1. The long-distance propagation of X-rays in the air will be hindered and scattered by the air, so it will be attenuated.

2. The rays emitted by the ray source are not parallel ray beams, but divergent, and the energy (energy area density) per unit area at the front end of the beam is inversely proportional to the square of the distance.