Light's Space Journey: A Unique Travel Experience

Light travels differently in space than it does on Earth. In space, light travels as a wave, but it behaves differently from other types of waves. For example, sound waves need a medium to interact with, such as densely packed matter, to travel. In contrast, light waves can move through space easily because they don't need a medium to travel through. This means that light in space is unhindered and will continue to expand outwards forever.

Light travels as a wave

Light travels as an electromagnetic wave. In fact, light is a type of electromagnetic radiation with a centre of the electromagnetic spectrum. Light is visible to the naked eye and is responsible for an organism's sense of sight.

The debate about the true nature of light has puzzled scientists for a long time. While Newton, in the 1700s, concluded that light was a group of particles, other scholars, including Grimaldi and Huygens, theorised around the same time that light might be a wave.

The wave theory of light was further supported by French physicist Augustin-Jean Fresnel, who mathematically proved light interference and hypothesised that space is filled with a medium called ether, which transmits light waves. In the 1800s, English physicist Thomas Young calculated light's wavelength from an interference pattern, further reinforcing the wave theory of light.

The concept of light as an electromagnetic wave was introduced by Scottish physicist James Clerk Maxwell in 1864. Maxwell's equations revealed the existence of electromagnetic waves and showed that light is a type of electromagnetic wave.

Light waves are different from other types of waves, such as sound waves, in that they do not need a medium to interact with or travel through. This unique property of light waves allows them to move easily through space.

Light doesn't need a medium to travel through

Light does not need a medium to travel through because its speed is experimentally constant, independent of the movement of the source or detector, or the direction in which it travels.

Sound, on the other hand, travels through the air or another material medium. If you are stationary with respect to the air, the speed of sound is the same in all directions. However, if you are moving with respect to the air, the speed of sound will be the same in all directions relative to the air, meaning that sound coming towards you will seem faster, and sound catching up to you from behind will seem slower.

If light were a disturbance in a medium, it would behave in the same way. But light never does—its speed is the same under all circumstances. Light is a wave in an electromagnetic field, and these fields are properties in space and time. They are not composed of atoms, so when they oscillate, there is no need for atoms to be present.

Light can travel through a vacuum, such as the vacuum of space, at a speed of 299,792,458 meters (983,571,056 feet) per second. This is a universal constant, known in equations as "c," or the speed of light.

Light from stars is sent out in all directions

The light from stars is made up of photons of energy, which are released from the surface of the star and are free to cross the vacuum of space. These photons travel in a straight line for millions, billions, and even trillions of years, unless they encounter something.

When we look at a star in the night sky, the light we see is the first thing those photons have bumped into since they left the star's surface. This is because stars emit light in all directions, and so only a small amount of the light is directed towards Earth.

The amount of light we receive from a star also depends on the distance of the star from Earth. The further away a star is, the less light from it will reach us. This is why distant stars appear dimmer, not because their light has dissipated, but because the amount of light we receive has reduced.

Additionally, the temperature of a star determines the main colour of light it emits. Cooler stars emit redder light, while hotter stars emit blue or white light. Colours like white or blue are stronger and can be seen more easily at far distances than reds, oranges, or yellows.

Light can be slowed down

In a vacuum, light travels at a constant speed of 299,792,458 metres per second. This is denoted by physicists as 'c' and is considered a universal speed limit. Albert Einstein's theory of special relativity is based on the idea that the speed of light is always constant.

However, light can be slowed when it passes through certain materials. For example, when light passes through water or glass, it slows down as the photons interact with the surrounding molecules. This is because light scatters off the molecules that make up different materials. The photons are absorbed by the atoms in the material, increasing the energy of the atom, which then loses energy by emitting a photon. This process repeats, causing a delay and giving the appearance that light is slowing down.

In 2001, scientists at the Rowland Institute for Science in Cambridge and Harvard University successfully slowed light to 38 miles per hour. They did this by shooting a laser through extremely cold sodium atoms, which worked like "optical molasses" to slow the light down.

While slowing down light is currently just a laboratory experiment, Lene Vesergaard Hau, the scientist who led the project, envisions future applications in improved communications technology, switches, and night-vision devices.

Light can be stopped

In recent years, researchers have been able to stop light for a few seconds using extremely cold gases and special crystals. In 2013, a team at Technische Universität Darmstadt stopped light for about one minute. They were also able to save images transferred by the light pulse into the crystal for a minute—a million times longer than previously possible.

In 2018, a study published in the journal Physical Review Letters proposed a new way to stop light at "exceptional points," or places where two separate light emissions intersect and merge into one.

The ability to stop light has significant implications for the development of vastly more powerful computers and more secure communication methods.

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