“It should be possible to explain the laws of physics to a barmaid.”
“When forced to summarize the general theories of relativity in one sentence: Time and space and gravitation have no separate existence from matter.”
-Albert Einstein
Atoms, the building blocks which make up our universe, are made up of 3 important elements: the proton, the neutron and the electron. You may have recognize this image from the Big bang Theory.
The protons are the particles in red and have a positive electric charge, the neutrons in blue and have no charge. Together they comprise the nucleus. The grey particles are the electrons, which have negative charge, and attracted to the protons, much like the moon is attracted to the Earth. They execute an orbital motion around the nucleus.
When a very high energy ray of light comes near an atom, it has a chance to spontaneously disappear and leave behind an electron and a positron (the antimatter counterpart of the electron. Like an electron, except with a positive charge). This is called pair production. At first glance, this is a very strange prospect, that a ray of light can spontaneously turn into matter and antimatter. But this process obeys all of the laws of physics (obviously, because it happens), i.e. conservation of momentum, conservation of charge and conservation of energy. Conservation of energy is achieved when you take into account the rest energy of the proton and the electron.
Einstein figured out that matter is a form of bundled up energy, which is described by the famous equation E = m, which says that the energy from an electron or a positron existing is equal to its mass multiplied by the speed of light squared. So if the energy of the light ray is more than twice m, with m being the mass of the electron or positron (both have the same mass), then conservation of energy is satisfied.
The figure above shows the light ray coming from the left near the atom, and transforming into the electron positron pair on the right. So it obeys the laws of physics, but why does it happen? And why does it have to happen near an atom?
Well it has to happen near an atom due to a subtle interaction between the atom and the light ray. Every atom produces electromagnetic fields, which the ray interacts with. The result of this interaction is probabilistic, the probability is determined by taking into account the total number of possible outcomes. It turns out, through the study of a field called quantum electrodynamics, that the probability that pair production occurs depends on the energy of the light ray, the higher the energy the more likely, and with the square of the number of protons in the nucleus, again, the more there are, the more likely. This interaction with the atom through its electromagnetic field includes it in the equation for the conservation of energy and momentum, which is why it is seen in the figure to have an extra momentum after the interaction.
Pair production is also a process which can happen backwards, in a process called pair annihilation. If you imagine running the process in the graph above backwards in time, i.e. the electron and the positron run into each other near an atom and annihilate each other to create a gamma ray, with all of the various conservation laws being obeyed.
References:
Image 1: Big bang theory: Why Leonard & Sheldon Spent exactly 139.5 hours rebuilding the model, https://screenrant.com/big-bang-theory-leonard-sheldon-139-hours-model-why/ , Accessed May 2020
Image 2: Conversion of energy into mass, https://www.jick.net/~jess/hr/skept/EMC2/node9.html , accessed May 2020
By Cian O’Toole.
The questions of “How did we get here?”, and “Where do we come from?”, have been asked by humans for millennia. The Greeks, Romans and Egyptians all had a shot at answering it before a modern day theory of the Big Bang became widely accepted. However, all good things must come to an end. This remains true for our very own Universe, where the manner of its demise is not so certain. Thus, the question remains. How exactly will the Universe end?
There are a number of theories about the downfall of the universe. Some end in a somewhat Biblical fashion, one in fire, the other in ice. Another theory may see us be ripped apart, atom by atom, as the Universe expands quicker and quicker. So, lets begin with the Big Crunch.
The Big Crunch:
The Big Crunch essentially sees the Universe do a U-turn on its current behavior. Currently, scientists know that the Universe is expanding, and has been expanding since its inception, approximately 13.8 billion years ago. No breaking news there. Simple knowledge of the laws of gravity would lead one to assume that after a certain time, enough matter in the Universe would accumulate together to halt the seemingly endless expansion of the Universe. This is the basis of the Big Crunch. Analogous to the phrase, “what goes up, must come down”, the expanding Universe will eventually begin to contract.
This would first be noticeable as the furthest objects in the observable Universe would start becoming more and more blue-shifted. Now what does blue shifted mean? Blue-shift, (and its opposite, red-shift), are due to a phenomenon called the Doppler Effect. You have experienced the Doppler effect many times in your life without even realizing. It is most easily observed when an ambulance approaches and then moves away from you. As the ambulance approaches, the siren seems to get louder and louder while also becoming higher in pitch. As it recedes away from you, the siren gets quieter and the pitch is lower. This is due to the fact that as the ambulance approaches, the sound waves become shorter, and as it recedes, they become longer. the same is true for light waves. The light of objects that are moving further away is stretched, leading to a longer wavelength. This is called red-shift as the longer optical wavelengths are the colour red. Conversely, the wavelengths of approaching objects are compressed, leading to a shorter wavelength. This is blue-shift as the shortest optical wavelengths are blue. Now, how does this lead to the end of the universe?
Objects that are further away in the Universe have a higher redshift, i.e. they are receding from us faster, the further they are. However, according to the theory of the Big Crunch, these objects would be the first to become more blue-shifted as they begin to stop accelerating away from us, and begin accelerating towards us. That is how the big crunch would initially be noticed by observers. From then on, everything in the Universe will begin to approach a common point, as gravity reigns supreme, the temperature always increasing. Eventually, everything will be condensed together to a single point, a singularity if you will. This singularity would contain all of the matter in the universe in an infinitely small, infinitely dense point. Does this sound familiar? Perhaps it should as this is how we currently believe the universe started out before the Big Bang. Theorists of the Big Crunch believe that this could then cause the birth of a new universe, which will then suffer its own Big Crunch, before having another Big Bang and so on and so forth in an infinite cycle. It’s poetic isn’t it?
The Big Freeze:
The Big Freeze theory can be considered to be the opposite of the Big Crunch. The Big freeze is more commonly known as the Heat Death of the Universe. Unlike the Big Crunch, where gravity ultimately brings all the matter in the Universe back to a singularity, in Heat Death, the Universe does not stop expanding. The previously used phrase, “what goes up, must come down”, does not apply here. In the case of Heat Death, it is similar to throwing a ball up, and as opposed to it coming back down (as one would expect), it flies away from you. Not only does it continue you to move away from you, it actually moves faster and faster the further away it gets. This is actually what is currently happening in our universe, the furthest objects are receding from us at a faster rate than those closer to us. It seems somewhat illogical.
The Universe can be modelled, believe it or not. The Universe can be modelled as flat, open or closed, with each resulting in a different ending for the future. The key element however to these models is the Cosmolgical Constant [1]. As opposed to the Big Crunch, where gravity wins outright (and seems the logical next step in the Universe), in reality, the cosmological constant prevents that from happening. The most plausible cosmological constant we currently have is that of Dark Energy, a mysterious force that enables the infinite acceleration of the Universe .
Over vast timescales, this will result in far-off galaxies disappearing from our night sky, as the expansion of the universe is receding quicker than the approaching light. This will continue for eternity until eventually all the galaxies are so far from each other, they are not visible in their night skies. There will be no more stars, no more nebulae and eventually all that will be left is black-holes. They too will eventually evaporate away as a result of Hawking Radiation, on an unimaginably long timescale. Entropy will win out. Everything will begin to approach the same temperature until a maximum entropy is reached, whereby all that will be left is an infinitely large, zero Kelvin universe devoid of matter.
Entropy can be thought of as adding milk to a cup of tea. Imagine before you add the milk, the tea is the Universe before the Big Bang. Once the milk is added, the colour changes (entropy increases). The entire history and future of the Universe takes place over a few seconds until maximum entropy (disorder) is reached. A uniform, pale brown is all you can see of your tea. This represents the Universe at Heat Death. The same in all directions at maximum disorder. It is quite a bleak future in store according to this theory.
The Big Rip:
The Big Rip, is a somewhat more thrilling theory for the end of the Universe, even if it is only in comparison to the infinite bleakness of Heat Death. However, it also incorporates Dark Energy as before. Yet, in the case of a Big Rip, the Dark Energy is not a cosmological constant.
Dark Energy can be thought of as a negative pressure [1]. This is a tough concept to get your head around, but can be thought of as analogous to pressure. Obviously. Whereas normal pressure results in a pushing force, negative pressure results in a pulling force, pulling objects apart. Dark Energy can be quantized as a ratio between itself (negative pressure) to the energy density. This parameter is called w. If w = -1, then the pressure and density are exactly opposite and the dark energy is a cosmological constant [1]. However, the value of w may not be equal to -1. This is where things start to get interesting.
In 2003, American physicist Robert Caldwell looked into what would happen if the value of w was to be less than -1 [1]. His findings were published in his excellently named paper, “Phantom Energy: Dark Energy with w < -1 Causes a Cosmic Doomsday”[2]. Here, Caldwell investigates the effects of a universe where w < -1. The results were astounding. Of w was found to be infinitesimally less than -1, the Universe would be destroyed. And you could also calculate how long this destruction would take [1]. But how exactly will this happen?
The largest objects will be the first to disperse. Galactic clusters will spread apart until eventually all that are left are individual galaxies. Then the galaxies themselves will be ripped apart, leaving isolated solar systems. This can be thought of as the matter being expanded by the space within all matter. Then stellar systems will be unbound, before planets themselves explode as they are quite literally being torn apart by the incessant Dark Energy. This continues until 10^-19 seconds before the Big Rip [2], atoms themselves will disassociate. The cores of blackholes will also be ripped apart before finally the fabric of space is ripped apart [1]. Quite morbid.
So How Will It All End?
Not in fire. That much is pretty certain. It is quite likely that the Universe will die due to a Heat Death. However, the possibility of a Big Rip cannot be ruled out, as all that is needed for this to occur is the cosmological constant w to be less than 1 be *any* amount. It is all a bit doom and gloom. However, the good news is, we will not have to worry about any of these for a very long time! So sit back, relax and enjoy the Universe while you still can.
References:
Additional information for this blog was taken solely from the following book:
[1] Mack, K., 2021. The End of Everything:(Astrophysically Speaking). Simon and Schuster.
With the exception of the Big Rip:
[2] Caldwell, R.R., Kamionkowski, M. and Weinberg, N.N., 2003. Phantom energy: dark energy with w<− 1 causes a cosmic doomsday. Physical review letters, 91(7), p.071301.
Infrared imaging and spectroscopy have become one of the most fascinating areas of modern research in physics, with applications ranging from the study of plant tissue structures all the way to investigating the structures of galaxies. Indeed, despite not being as flashy as the String Theories or General Relativities of the world, the science behind IR imaging has become a somewhat pivotal part of modern technology and provides a key insight into the fabrics that make up our universe.
So, what is IR imaging? IR, or infrared, refers to a specific wavelength band of the electromagnetic spectrum, with IR waves being slightly longer than visible light and shorter than radio waves.
FIG.1. The electromagnetic spectrum, with IR light highlighted [1]
IR Imaging in Medicine
Perhaps the most well known and what can be considered the most useful application of IR imaging with regards to general society is its use in medicine. Infrared thermography has been present within the medical landscape for decades, beginning in 1928 when Professor Czerny in Frankfurt presented the first IR image of a human body. This was the first time that technology could be used to accurately describe the temperature/radiation produced by nearly any part of the human body, all without even making contact with or interfering with the measured skin.
Of course, with all discoveries made in history, there were, and still are some drawbacks. In the beginning these were associated with poor thermal and geometrical resolution, the original prototypes not offering the highest in quality or perhaps even usability, as the stability and exact measurements were often questionable. The biggest downside, however, was its reproducibility. It was often too expensive to build even the most basic infrared cameras. This was due to many reasons: the unavailability of the required natural resources as well as the heavy machinery required in the construction, the manpower required to operate and build such machinery as well as the believe that with x-rays being as successful as they were in the medical field, the use of IR imaging would not be required.
Most of these obstacles were overcome eventually, through funding from large corporations as well as the invention of better and more cost-effective cameras. Despite the setbacks experienced, the end products have been able to pave the way for a new era of disease detection. IR images are used to show abnormally increased focal surface temperature on specific parts of the human body, which are related to radiation produced by cancers, tumours, etc. There have also been uses in rheumatology and orthopaedics, neurology as well as vascular imaging.
FIG.2. Breast cancer detected from radiation spike [2]
IR Astronomy
The use of IR imaging has not been limited to use on Earth; it has managed to make its way to our satellites and probes travelling into the farthest reaches of space. Infrared astronomy is an area of active research that is hugely beneficial in the understanding of galaxies, stars, planets and other astronomical structures. It involves both the imaging of structures in space based on their infrared radiation and the spectroscopic analysis of electromagnetic radiation in the infrared range that either comes from or passes through astronomical structures., which gives information about the composition of astronomical objects.
FIG.3. Two pictures of the Orion constellation, the left being an image in the visible spectrum and the right in the infrared spectrum. This shows the power of making observations outside the visible spectrum, allowing us to observe much more detail [3]
Many observatories and telescopes are capable of detecting infrared light and there has been a significant amount of telescopes specifically designed to detect infrared light or have instruments for which infrared light can be detected. These include ground-based telescopes, airborne telescopes and space-based telescopes.
FIG.4. The infrared windows of our atmosphere
Applications to Agriculture
One area one might not expect to see IR imaging methods and more specifically spectroscopy is in the agricultural and food industries, but in fact it has been in use for decades.
Today the powerful compositional analysis provided by various spectroscopic methods is invaluable in the production of food and other agricultural goods. Traditional methods of determining the quality of produce are often time consuming, destructive and have a negative impact on the environment due to the use of harmful reagents and intensive water costs.
Spectroscopy, specifically in the Near-IR and Mid-IR regions are employed in all areas of the agricultural industry, from soil analysis, (one interesting example close to home being Johnstown Castle), to post-harvest produce quality control. Quality control is a theme when it comes to NIR spectroscopy; an example of which is its use in the grain industry where it is used extensively in the study of the characteristics of flours and grains. Using this technology flour mills can quickly determine the nutritional value and moisture content of wheat and flour, allowing them to ensure it is up to standard. Another example is ensuring that the crisps in your cupboard stay crisp and are uniformly flavoured. Seabrook Crisps in Bradford, UK, have employed the use of an NIR spectrometer to ensure their flavour machine is running optimally by performing tests throughout the work shift and between flavour changeovers. By testing the spectra of crushed crisps the machine determines the percentage of flavouring present, if this flavour concentration was not within specification the flavour application machine is recalibrated to deliver the optimal, even coated crisp.
MIR and specifically Fourier Transform Infrared (FTIR) spectroscopy is an important method in managing the quality and safety standards of fat and oils used in the preparation and production of food. A large problem when storing and processing fats and oils is deterioration due to oxidation when in contact with atmospheric oxygen. This reaction produces hydroperoxides which can further break down into many secondary oxidation products, giving rise to an off-taste and bad odours. Therefore the oxidative stability of an oil is an important factor when considering the quality and stability of oil and FTIR spectroscopy provides an effective means to test the oxidative state of an oil. This is done by measuring the chemical concentration profiles of important oxidation products such as hydroperoxides using FTIR spectroscopy.
Where to next for IR imaging?
Of course, as is the case with most modern technologies, the use of AI and machine learning algorithms in IR imaging has led to many interesting advancements in the field. For many, the thought of AI technology slowly creeping into more of our lives isn’t the most comforting thought. It cannot be denied however that these new technologies possess a vast well of potential when it comes to advancing our current systems, with a few notable possible applications to the world of IR imaging.
Machine learning is a way of creating artificial intelligence, by programming a computer to make a decision, and telling it when the decision was correct. By repeating this process, the computer gets better answers each time, and you eventually create an algorithm that can accurately make the right decision. This can be applied to many different areas of technology, including thermal imaging technology.
FIG.5. [4]
Looking further afield, IR sensors can be integrated into drones and together with deep learning algorithms can be used to identify ground-nests of birds on agricultural land before being damaged by machinery.
FIG.6. [5]
To sum up, it’s clear that the areas of IR imaging and spectroscopy have a wide variety of applications to modern science and certainly possess a lot of potential for further development into the future.
REFERENCES
[1] https://lab-training.com/2015/07/04/electromagnetic-spectrum-regions-of-interest-to-the-chemical-spectroscopist/
[2] https://www.researchgate.net/figure/A-48-year-old-woman-with-right-breast-cancer-IR-imaging-shows-abnormally-increased-focal_fig3_40893985
[3] Encyclopedia Britannica
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=12307&button=recent