How
information reaches us is a very basic question and the answer is that through
radiations. Now your next question will be who produces or re-emits the
radiations? According to research so far, all objects in the universe emit
radiation.
For example, black holes or events like the Big Bang, supernovae, planets, stars, clouds, space clouds and even life forms also emit radiation and that radiations brings information to us even from miles away. So your next question will be that stars can emit radiation but how planets can emit radiation so here I want to tell you that your own body also emits radiations. If we look at our body using a thermal camera, we can observe that our body is absorbing temperature and emitting different types of radiations. And these radiations can stop if all the molecules in our body gradually stop their vibration i.e. when our body start moving towards absolute zero. When molecules and atoms start moving towards absolute zero state, their movement and vibration ceases and then they will not radiate, but this is an extreme case. So all the information that reaches us is through radiations.
So we can also call radiation as information carrier, some of which are named as follows: -
Radio
Wave
Microwave
Infrared
Ultraviolet
rays
X-rays
Gama
rays etc.
We
have created a spectrum chart and classified them by sorting out that which
sources of radiation produces which types of radiations. For example, the sun
is producing almost all types of radiations.
Let me tell you that there are some radiations which are not produced by the sun but are produced by many celestial bodies. So we try to observe a star in visible light and understand how it works (as shown in below).
As we can see in above, the star is producing a continuous spectrum of visible light. But there is a cloud between the star and us. This cloud absorbs some radiations or wavelengths, that is shown as the black spectrum or the color absorbed by the cloud. Now the spectrum we get after that, includes the continuous spectrum of the star along with some clues and by this we know that there is a cloud between the star and us. Through these clues we can also find out that, what the cloud is made of. Because each element has its own emission spectra. We have tried to show the emission spectra of all the elements of the periodic table in below.
Since we are discussing about information carriers, how can we ignore Einstein's field theory. According to Einstein's field theory, these information carriers reach us through space-time. Space-time is a model used to describe space, with three dimensions of space and one dimension of time. To better explain this you can see it as a sheet in a figure below.
When a mass or an energy is placed inside it, a curve is formed and because of this curve we see can motion. When there is a disturbance in this space-time, certain types of waves reach us called gravitational waves.
As on one side there were theories that electromagnetic waves convey information to us but on the other hand Einstein told that gravitational waves also exist and these waves also give us information about an event or a celestial body. Till now we have found 70 different types of sources that produce gravitational waves. For example, if a mass is orbiting another mass, it will give off gravitational waves. If body show a lot of change or rapid change in its spine, it can also give us gravitational waves. If two objects collide or merge, the gravitational waves will also produce there.
Similarly, the quantum fluctuations produced after the Big Bang Theory are also providing us their information through the gravitational wave. Einstein's Gravitational Wave Theory tell us that we have also another medium which give us information that we didn't know about before this century. We are receiving patterns of information, that are not part of the known electromagnetic spectrum. Maybe in the future we will find some other sources that are not even part of the gravitational spectrum. We desire here to tell you that the at some times the speed of gravitational waves and electromagnetic waves can be equal to the speed of light. Like electromagnetic waves gravitational waves also have amplitude and frequencies.
We have built many sensors to detect these gravitational waves, like two in US, one in Japan, one in Russia and one in China.
As gravitational waves reach the earth from different orientations but at a time we can place our sensors in one direction on Earth, which means we can measure limited gravitational waves with these sensors. So, there are many gravitational waves passes through the Earth without detected. Because the direction or orientation of these waves varies depending on the direction of our sensors. In future we are going to build sensors in space to measure low amplitude gravitational waves. So, the future astronomy, is gravitational astronomy.