A Few years back a paper in the prestigious Physical Review Letters (see here) has claimed that they found a holographic model of our Universe can explain the data on Cosmic Microwave Background Radiation (CMBR) better than the standard cold dark matter model of cosmology (Lambda-CDM model). What does this result really mean to a common person? Well, if we try to decipher it then we find, one set of model is found to be better than the other type of model to explain some data on the properties of our Universe. And in that sense, there is nothing new. This always happens in scientific study. But the puzzling thing is that the better model appears to be a model which envisage our Universe to be a hologram. Wow! that is quite dramatic!
Almost all the objects we see around us are 3-dimensional, means they have length, breadth and height. On the other hand hologram in our daily life is a piece of 2-dimensional sticker inside which a 3-dimensional image appears to be embedded in. Now if we are to believe that our Universe is a giant hologram, then it would mean that our objective reality is nothing but an illusion! If true, it would bring a paradigm shift in the perception of our Universe.
Thus you see this is worthy of something that should be pursued further. So, let’s delve deeper and find out what is really being said here.
History of our Universe: To know the history of our Universe we have to go back in time, 13.7 billion years back. Let us start with the present. At present, our Universe is uniform (homogeneous and isotropic) on a cosmic scale (a cosmic scale is a distance of millions of light-years). The current understanding of our Universe indicates that it is expanding and galaxies are moving farther away from each other. It is not like the galaxies themselves are moving farther away, rather the space-time which holds these galaxies are expanding. As a consequence, the distance between galaxies is also increasing. Let us illustrate this expansion with the help of a rubber membrane. Mark any two points on the membrane. If we stretch the membrane the distance between the two points will increase. The membrane here is the space-time and two points are two galaxies. Now if we travel back in time, then we would find our Universe to be contracting until it converges to a point or very small region of space-time. That point is called the ‘Singularity’. Our Universe started its journey from this singularity with a bang! a violet explosion releasing an unimaginable amount of energy. The phenomenon is known as Big Bang.
Timeline of the evolution of our Universe. Image credit: Rhys Taylor, Cardiff University
Ever since it’s birth in a hot dense state, the Universe is expanding and thereby cooling its’ temperature. The story of the evolution of the Universe roughly goes like this: shortly after (10-35 sec) the birth, the baby Universe underwent a brief period of rapid expansion known as inflation (still a conjecture!). The expansion speed was so rapid that it even exceeds the velocity of light. After the period of violent expansion, the Universe continues to expand but at a much slower rate. By the time elementary particles appeared, forces of nature as we know today, manifested in its current form. The expansion continues and at some stage, quarks get confined within protons and neutrons (quarks are the elementary particles that made up the protons and neutrons). Later on, atomic nuclei are formed. But the formation of a neutral atom is still far away as the thermal speed of the electrons was so great to bound them within the confined boundary of the atoms. All these events stated above was completed within 1 minute after the Big Bang!
Other features of the Universe start to appear at a much much later stage compared to this time scale. It took a few hundred thousand years for neutral atoms to form. With time those neutral atoms coalesce forming gas clouds. These gas clouds at later stage give rise to stars. With the evolution of the Universe, those stars slowly start to form groups out of their gravitational attraction. Those groups will later on form galaxies. And slowly the Universe starts to take our present form. Our solar system comes into being at a much later stage, about a few billion years after the Big Bang when our Universe was grown to two-thirds of its present size.
तमसोमाज्योतिर्गमय (Tamso Ma Jyotirgamaya): The account of the history of our Universe presented above sounds good. But without evidence, the scientific exposition would reduce to a work of fiction. That evidence can be found in the form of radiation coming from the early stage of evolution of our Universe. It is a story of going towards the light from the darkness.
Shortly after the Big Bang, the Universe was hot dense soup (plasma) of particles like electrons, protons, photons (light carrying particles) etc. The photons got scattered and re-scattered from the electrons, protons of the soup making it hard to escape. Our Universe was in the dark and foggy state. As time passes, those protons and electrons bind together to form neutral atoms. And when it happens, the light (photons) got a chance to escape carrying the message of the early Universe. Those photons can still be seen in our present-day Universe in the form of radiation known as Cosmic Microwave Background Radiation (CMBR). Now questions come to your mind why can’t we see it when we look at the night sky with our naked eye or an optical telescope? The space between stars and galaxies all appear to be dark.
Well, you need a special type of telescope to see the glow – a radio telescope. When photons travelled through the expanding Universe, it’s wavelength got increased. The value of this wavelength falls into the microwave part of the electromagnetic spectrum and thus the name Cosmic Microwave Background Radiation. Several experiments have been performed to detect and characterise the CMBR to date. Among them COBE, WMAP from NASA and PLANCK mission by European Space Agency are notable. According to the available data, we come to know that the cosmic radiation is uniform in all direction with an average temperature of 2.7 Kelvin. But, tiny fluctuations here and there around this average temperature have been observed. As the saying goes, The devil lies in the details. The understandings of those tiny fluctuations are extremely important. This would not only reveal the information regarding the anisotropy of our Universe that persisted right after the Big Bang but will also reveal the details of the large scale structure formation (like a galaxy) in the Universe.
The Cosmic Microwave Background Radiation. The warmer regions are shown in red and the cold regions are shown in blue. Image Credit: European Space Agency
Holographic Universe: A detailed understanding of those tiny fluctuations in CMBR is an active area of current research. In this context, the paper mentioned at the very beginning of this article considered two models as viable candidates to explain the observed data on CMBR. Among the two models, they found the holographic Universe model can explain the data in a slightly better way than the standard model of cosmology. This positive result inspired the practitioner of the model to pursue their ideas further. While for us, the common people, the idea “Holographic Universe” is a little disturbing. So let’s find out what the idea suggests.
In physics, there is a principle called duality. It is a connection between two theories/models. Information from one theory/model helps us to extract information about the other. Consider for example two languages. If you have the dictionary then you can always switch between two languages easily using the dictionary. The holographic model of the Universe exploits the duality between volume and surface. Let us illustrate with an example. Suppose you want to know how many people work in a particular organisation on a particular day. Assume the shape of their office is like a football. They have installed electronic attendance machine on the surface of the football. Now to know how many people are working on a particular day, you can go inside and count each people. Otherwise, you can also collect data from the electronic attendance machine installed at the gate and easily count the number of people. Here going inside the football can be compared with the collecting information from the volume and collecting data from the gate can be compared with the information contained at the surface. Thus we see, the information contained in a volume can be obtained from the information stored at the surface. The connection here is the electronic attendance machine. Mathematically speaking the volume can be represented as a hologram of the surface. This is the principle that the holographic model of the Universe uses. And it is quite different from the fact that our Universe itself is a giant hologram. Hope it is now clear that our apprehension for the term holographic universe was misplaced. The name stems from the underlying mathematical principle used. It remains to be seen (if true) what will be the consequences of this model. But it can be safely assumed that there will be no observable difference to our naked eyes. Though a subtle difference at the cosmic scale may be expected.
Scientific progress is always incremental. Successive small steps constitute a great leap forward for human knowledge. We hope one day models like standard model of cosmology, holographic model of the universe will be able to shed light on the different unresolved areas of the early Universe and led us to the path of illumination from ignorance.
Trivia: Are you interested to listen to the sound of the Big Bang? A noise that is as old as our Universe, carrying the message from our baby universe. (Audio Clip credit: (c) John G. Cramer – 2013, please visit his website for details and longer version of the clip)
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