In this chapter we will learn what the cosmic background radiation is, and how it is measured
"During the month of March 2014, we received the first experimental confirmation that the universe underwent an accelerated expansion a fraction of a second after the Big Bang and further confirmation of Einstein's theory of general relativity. This is how we expand our understanding of reality and take another step closer to a theory of everything and to a complete understanding of our universe and how it was created. Welcome to the fourth part of a brief history of the universe! In this series we will review both the insights we have been able to reach to date in the field of cosmology
- Genesis was empty - how was our universe created? - Part a'
- Genesis was empty - how was our universe created? - Part II'
- Genesis was empty - how was our universe created? - Part III
As explained earlier, after the Big Bang, radiation and matter were created. As long as the universe was in the "hot particle soup" state, radiation was absorbed by particles and emitted by particles continuously. Only after 380,000 years since the Big Bang, when the first atoms were created, could radiation travel unhindered in empty space. As time passed the universe continued to expand and stretch and as a result this radiation cooled and went away. Its frequency decreased until it reached nowadays the cold frequency of microwaves. Since the radiation could travel in empty space and until we received it, it traveled unhindered until it reached our devices sensitive to the frequencies of the microwave radiation. Think about this strange situation, in every direction we point an antenna that is sensitive to microwave radiation we receive signals from space and these signals are exactly the same frequency even though we measure them in opposite directions in the sky. How can it be that in different directions in space we will have exactly the same radiation? The explanation is that all this radiation came from one common source and therefore the radiation looks the same. The source is of course the big bang and because immediately after the bang the universe was very small, the radiation could spread without a problem throughout the universe. This is how we can explain why we measure the cosmic background radiation in every direction in space and at the same frequency and temperature. The low frequency and temperature of the cosmic background radiation gives further confirmation that the universe began with a big bang exactly 13.8 billion years ago.
The cosmic background radiation is amazingly uniform across space, the same temperature and same frequency everywhere. In the nineties, another experiment was done to check how uniform this radiation is. A satellite named Cobe orbited the Earth and collected samples of the cosmic background radiation at various locations in the Earth's orbit around the Sun. The results were impressive, he found that the temperature and frequency of the radiation is exactly the same everywhere up to 0.00001 degrees, and only after six digits after the decimal point do you start to see differences in the temperature and frequency of the radiation. These are minor differences! But these differences are important for the formation of stars and galaxies in the universe. The uniform radiation corresponds to the fact that there was a hot and uniform "particle soup" (like a hot soup in a pot where all the ingredients are mixed and uniform). When the atoms were created, they too maintained this uniformity. But if all the matter and radiation were so mixed and uniform in space, how could large and uneven structures like stars and galaxies form?
Unlike in the primordial soup period, when we look at the universe it does not look uniform, it has regions of matter of stars and galaxies and clusters of galaxies and in between there are huge regions of emptiness (and cosmic background radiation). In addition, for a star to form, the uniformity of matter must be broken. There should be places that are slightly denser than other places, so that more material will collect there and therefore there will be a greater gravitational force there than in other places. This gravity will attract a little more matter to it than other places attract and so over long periods of time enough matter will concentrate in a small area, attract each other, collide with each other, heat up and form a star. For this you need deviations in the distribution of the material in the hot soup, these deviations in the material will cause deviations in the cosmic background radiation (the radiation is absorbed a little more in the area where there is a little more material). That is why the small deviations that were discovered in the radiation were very important, they are the evidence of small deviations in the uniformity of the material. Deviations that will lead to the creation of the stars and star clusters (galaxies). And indeed, the small deviations we discovered in the cosmic background radiation along the sky are exactly in the regions where we see galaxies today. The process of creating stars takes a long time, it is estimated that only after about a billion years since the big bang did the first stars appear.
In the beginning there was nothing. was empty
A ripple of energy appeared from the void,
The Big Bang - the creation of space-time
The universe began to expand (and there is no meaning in the question of where)!
The symmetry is broken, the union is cracked
The force of gravity from the unified force is discharged
Then came the turn of the powerful nuclear force
The electromagnetic force is separate from the weak nuclear force
The particles were formed and gained mass quickly
A hot ancient soup was getting colder
The particles to atoms began to connect
The background radiation was on its way
The atoms connected to each other without problems
Stars were created out of deviations
The stars formed structures and galaxies
Dark energy meanwhile accumulated
And the expansion of the universe increased again
The inflationary universe model
Note the considerable amount of experimental confirmations we have already collected to date for the big bang theory and the age of the universe. The expansion of the universe, the cosmic background radiation that has the appropriate frequency and the appropriate uniformity and has the appropriate deviations. All these findings agree with each other and confirm that our universe began 13.8 billion years ago with a big bang (and let's not forget the discovery of the Higgs particle which is another support for the electro-weak union and the union of forces). But more insight into the evolution of the universe was needed to explain how the stars and galaxies formed. Several problems were discovered in the Big Bang model that needed to be solved. There are regions very far from us, on both sides of the universe that we are able to see. Also there, of course, is the cosmic background radiation with the uniform temperature. Calculations have shown that when you take these distant radiation regions and try to bring them back in time, it seems that the time since the beginning of the universe is not enough for them to converge like the rest of the matter into one point. In other words, these regions are too far away and do not seem to have been at the point of the Big Bang at the time of the Big Bang. They are so far apart that there was never any connection between these areas. But if there was no connection between them at all, how could they have the same temperature and the same frequency (what are the chances that you will look through a telescope at distant buildings and find kitchens with coffee cups in all of them and all of these cups have the same temperature? To explain this, it should be said that all these different cups started their journey from a jug Shared coffee and therefore all at the same temperature, but then it will turn out that some of the cups are too far from each other and they were never in the shared carafe)?
Another problem was discovered, it turns out that the deviations we discovered in the cosmic background radiation are too small to explain how enough material was compressed to form stars. The problem is that the universe started out too hot and too uniform. He was in a state of great disorder. In physics we measure disorder with a quantity called entropy. The greater the entropy, the greater the disorder of the system. A uniform state corresponds to a state of great disorder or great entropy. As in the hot soup, there is great disarray, all the ingredients, the carrot, the water, the soup powder (for the lazy among us), the celery, everything is mixed up and it is impossible to know where each ingredient is. If so, the universe began in a state of very high entropy and since then it cooled and order began to increase. But here lies the problem. There is a statistical principle that is a kind of law of nature called the second law of thermodynamics, it claims that in a closed system disorder can remain the same or increase but not decrease. We see this second law in action all the time, a house left to its own devices gets messy over time, the piles of white and black socks in my closet get mixed up over time, a glass can break and thus disorder will arise but we don't see an opposite situation where broken glass will suddenly gather and form a whole glass . To lower the disorder, the system must be opened and new energy introduced into it. Is the house messy? We will put new energy into the system, in other words we will take a broom and clean the house (or, for the lazy, we will invite someone to clean for us).
According to the second law of thermodynamics disorder should increase with time, not decrease. How, then, is it possible that our universe began in a state of great disorder and over time the disorder became less and less? There is a contradiction here to the second law of thermodynamics! Especially when we remember that the universe is everything that can be measured. The universe is the largest closed system there is, there is nothing else outside of it, there is no way to add energy to it from another system. The universe began with enormous uniformity and entropy and for some reason the order grew over time and stars and galaxies formed. One could perhaps expect that if this is how we measure today the second law of thermodynamics is reversed as time goes by the order only increases. This was appropriate for the events that occurred after the big bang, how did we suddenly get an opposite situation where the entropy of the universe only increases and never decreases? What is the solution to this problem?
For these reasons and others, a physicist named Alan Guth proposed in the early 10,000,000,000,000,000,000,000,000s the inflationary universe model (or the inflation model in Hebrew). According to the model, after the big bang, while breaking the unification of forces, the universe began to expand at an extremely rapid rate. Space-time expanded at an enormous speed, higher than the speed of light, and thus there was "inflation" in the size of the universe (according to the theory of relativity, the speed of light is the highest possible speed at which matter or information can move. But space-time is not matter and does not transmit information, therefore it can move above the speed of light). The volume of the universe increased within a millisecond by 25 (one followed by 0.0000000000000000000000000000000001 zeros). According to the model, the time when this cosmic inflation occurred is about a thousandth of a second and it started with the separation of the strong nuclear force from the other forces (remember when?) about 34 seconds after the big bang (1,000,000,000,000,000,000,000,000,000 digits after the decimal point) with a temperature of 1 ,27 (XNUMX followed by XNUMX digits) degrees Celsius. Today, when we discovered that the expansion of the universe is accelerating again, we suspect that the same mysterious dark energy is also responsible for the period of inflation immediately after the Big Bang.
If the swelling model is correct, we can get explanations for the problems that arose. Although it seems that the cosmic background radiation found in regions far from each other did not begin at the point of the big bang, but we did not take into account that there was a period when the universe accelerated its expansion. If the universe always expanded at the same speed these distant regions really could not have started from the same point and moved so far apart from each other. But because there was an inflationary phase in which space expanded at a dizzying rate, these regions did begin in the Big Bang and were close but were separated and moved apart significantly during the inflationary phase. And what about the problem of order and disorder? The universe did indeed begin in a state of great disorder and uniformity. Because according to quantum theory there are always small fluctuations, even in this uniform state there were small fluctuations and deviations from uniformity (the small deviations measured in the cosmic background radiation are echoes of this phenomenon). As we have seen, these deviations are still not enough to form stars and galaxies, but now the inflationary period of the universe must be taken into account. This rapid expansion of space-time magnified these small deviations to dimensions large enough for the material there to stretch enough to form stars and then galaxies and galaxy clusters. In addition, as we have seen, the more you increase the volume, the lower the temperature. Following the period of inflation, the volume increased so greatly that the universe became mostly cold and empty. In the inflationary phase the expansion was so strong that the matter that went through this tremendous expansion melted together with space-time. The spaces between the particles have increased significantly and a huge amount of empty space has been added between the particles. In this way, isolated and relatively isolated islands of dispersed material were formed within the vast volume that was suddenly created. This is a very orderly situation, we know where the substance is and where the rest of the empty space is (like for example an orderly situation where perfume is in small bottles around a large room). Here it is, with the help of the period of tremendous expansion of space-time we managed to get from a state of high disorder after the big bang to a state of high order after the period of inflation. And what happens when starting from a high order state? If the perfume bottles are open, we will see that over time the perfume evaporates from the bottles and a pleasant smell fills the volume of the room. In other words, the disorder is growing and we will no longer be able to separate where the perfume is and where there is clean air. So also the matter in the immense universe, begins to spread within the enormous volume and increase the disorder. This is how we arrived at the second law of thermodynamics in which the entropy will remain constant or increase in a closed system.
The experiment that confirmed the inflationary universe model
Since the XNUMXs, the question has remained open as to whether the universe did undergo an accelerated and enormous expansion right after the big bang. The experiment, the results of which were published about two weeks ago, answers this question in the affirmative. The results are consistent with the universe undergoing inflationary expansion!
The experimental team was able to skip the energy gap and find echoes for the short and energetic inflation period. How did they manage to measure a phenomenon that happened so shortly after the big bang when the strong nuclear force separated from the unified force? with the help of gravity waves.
Einstein's general theory of relativity has already been confirmed in many experiments and our GPS devices work well thanks to it. But one of Einstein's predictions was not verified until the results of the last experiment, this is the phenomenon of gravitational waves. According to the theory of general relativity, gravity is actually space-time that has been curved (just like a straight surface that has been curved into a sphere, only that space-time is four-dimensional and is curved into a four-dimensional sphere). One of the solutions to the equations of relativity shows that space-time can vibrate cyclically like a wave. This is a gravitational wave. We are used to waves moving on the surface of water or in the air, but in this case it is a wave created due to the curvature of space-time itself. Gravitational waves are very weak and therefore difficult to measure, to date we still have not been able to create or measure gravitational waves directly (including in the current experiment). How do we even know if a gravitational wave is passing through here? When we measure the area where the gravity wave passes, we will find that the space there stretches in a certain direction and shrinks in the perpendicular direction:
Although it is difficult to measure gravitational waves directly, the team of physicists who conducted the experiment realized that both the existence of gravitational waves and the inflationary universe model could be confirmed at once by indirect measurement. They will try to measure a phenomenon that cannot be explained except with the help of gravitational waves and could only exist if the universe went through an inflationary period. The phenomenon is called polarization and they were looking for a specific polarization of known magnitude that should be caused by gravitational waves only during the inflation phase. Polarization means that the wave moving in a certain direction can oscillate along its path in several different directions.
The following image explains what polarization is
This coming June, Nir Lahav plans to give lectures on this topic as part of the series I give at cinemateks across the country, the science and reality research series (in the month of April, the lecture will be at the end of Holocaust Day on the topic: Is man's nature evil from his youth?) Please follow the blog posts free and happy.
More of the topic in Hayadan:
- First direct evidence of the existence of gravitational waves that caused the universe to swell immediately after the big bang - an interview with Prof. Avi Leib from Harvard University, the head of the department of the main researcher who performed the experiment
- We received an important message from the fraction of a second after the Big Bang - an interview with Prof. Mark Kamionkowski who devised the experiment
- How does the telescope at the South Pole that discovered the gravitational waves created by the Big Bang work?
- What are gravitational waves?
- An attentive ear to the echoes of the Big Bang