THE FIVE STRANGEST EVERYDAY OBJECTS

Over the years, the articles on this website have become increasingly in-depth and complex, so that understanding many of them (especially those related to fundamental physics) requires a moderate-to-high level of knowledge of physics and mathematics. In this article, we will use only high school mathematics and physics (and a little basic relativity and quantum mechanics for a little more depth) so that the text is understandable to anyone with a basic understanding.

As we've explained countless times on this blog, modern physics is full of fascinating phenomena. However, most of these phenomena seem so distant and alien to our everyday lives that we barely pay attention to them. However, sometimes these exotic phenomena "sneak" into our everyday world without us even realizing it. In this article, we'll look at five everyday objects whose behavior cannot be explained by "ordinary" physical laws but instead require recourse to the "exotic" physical laws of relativity and quantum mechanics.

Welcome to a strange and exotic world: our everyday world!

1st) MERCURY THERMOMETERS

Readers who are not too young have probably used a mercury thermometer at some point. Apparently, the liquid inside the thermometer doesn't seem very special, but mercury is a very strange material: it's a liquid metal at room temperature. Intuitively, this is very strange; we always think of metals as solid, rigid materials that must be heated to very high temperatures to transform into liquids. Let's look at the chemical element most similar to mercury: barium. Barium has a chemical configuration almost identical to that of mercury; however, barium is a solid metal at room temperature, and to liquefy it, it must be heated to 727°C! How is this possible? How can two elements with such similar chemical configurations have such different properties? To answer this question, it's not enough to resort to physics and "everyday" chemistry; we must resort to "exotic" physics: special relativity.

As we know from our high school chemistry classes, the electrons within an atom are distributed in the form of "shells" called orbitals. Each orbital has a characteristic energy within the atom. We will also remember from high school classes that only the electrons in the outermost shell determine the chemical properties of an atom, since these electrons are involved in chemical bonds with other atoms. The number of electrons missing to complete this last shell is called the valence number. In solid materials, the bonds between atoms are stronger; in liquids, they are weaker; and in gases, they are practically nonexistent. In the case of metals, the nuclei of the atoms are very close together, creating a three-dimensional structure, and the electrons in the outer shells are shared with other atoms to form the metallic bond.

The electron configuration of Mercury is:

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2.

The outermost orbital is the 6s and is filled with its two electrons.

The electron configuration of Barium is:

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2.

The main difference between the two elements is that Mercury has more protons than Barium, and therefore the electrons in the former have to spin faster to compensate for the greater electromagnetic attraction of the nucleus. Now comes the interesting part: Above a certain speed, relativistic effects begin to be important. In the case of Mercury, the electrons move at 58% of the speed of light. The equations of special relativity tell us that at this speed, the effective mass of the electron increases by a factor of 1.23. This results in an increase in angular momentum and a 23% reduction in orbital size. This means that Mercury's 6s electrons are closer to the nucleus than in barium. This causes the outermost electrons (valence electrons) in Mercury to be in the 5d orbital instead of the 6s2. However, the 5d orbital is fully occupied, which means that these electrons are not shared with other Mercury atoms, and therefore the metallic bonding typical of metals cannot be effectively achieved . In this way, the bond between mercury atoms is very weak, and the macroscopic consequence is that mercury is liquid at room temperature. So the next time you hold a Mercury thermometer, you should remember that the liquid inside owes its properties to the "magic" of special relativity.

2nd) RADIOACTIVE INJECTIONS IN THE HOSPITAL

Perhaps some of you readers have had to undergo a PET (Positron Emission Tomography) scan. This technique is used to visualize internal organs and detect possible pathologies by analyzing their metabolism. Before the test, the patient receives an injection of a liquid called a "radiopharmaceutical." Perhaps you don't know that this liquid contains very special components: radioactive isotopes that emit positrons! But why is the nurse injecting me with a radioactive material?

The most commonly used radioactive isotope in PET is F-18 fluorodeoxyglucose, a glucose analogue. This radioactive isotope has an ultrashort half-life and, when injected into the patient, emits positron radiation (this radiation is very weak and practically harmless). Positrons are the antiparticle of the electron and are essentially positively charged electrons that, when they react with the electrons in our body's organs, produce high-energy radiation: gamma rays.

As if we were in some kind of superhero comic, this medical test turns us into temporary gamma ray emitters!

This radiation is easily detected and differentiated from environmental radiation by the scanner's sensors, which create a three-dimensional "image" as the positron-emitting fluid moves through the patient's body. Various diseases, such as cancer, produce an increase in metabolism in infected organs. This increased chemical activity increases glucose absorption, causing the organ with cancer cells to "glow" much more brightly than the rest. In this way, it is possible to detect numerous diseases in the patient. This is undoubtedly another spectacular example of the power of science at the service of human health.

3rd) HOLOGRAMS

Holograms are capable of reproducing a three-dimensional image from a two-dimensional plate. The key is that the two-dimensional image contains information not only about the amplitude (intensity) of the light but also about the phase of the incident light beam (remember that light is a wave and therefore has a characteristic phase). To record a hologram, we interfere with the light coming from the object we want to recreate with the light from an external source. By interfering the two beams, we obtain information about the light intensity and the angle (phase) of the light:

In the image, the white dot is illuminated by plane waves coming from the left. Some of the light is reflected off the dot, which emits spherical waves to the right. These reflected waves interfere with the plane waves illuminating the scene. Where crests meet crests and valleys meet valleys, there will be maximum amplitudes. Symmetrically, where crests meet valleys and valleys meet crests, the amplitude will be minimum. If we place a photosensitive plate in the dotted area of the image, the areas where the amplitude is maximum will be more transparent and the areas where the amplitude is minimum will be more opaque. This way, information about the phase of the incident light is recorded on the plate.

To observe the hologram, we illuminate the plate with a laser beam. The most transparent holes in the plate correspond to points on the object that are in phase, that is, have the same angle; the slightly darker holes correspond to points on the object that had a small phase difference, and the darkest holes correspond to points on the object with a larger phase difference. Since the phase difference is essentially proportional to the distance between the points, the difference in brightness encodes the distance between different points. Thus, by illuminating the plate, an observer located to the right of it will observe light coming from the plate that has the same amplitude and the same phase (which encodes the distance between points) as the light from the original object; that is, they will be seeing a three-dimensional image of the original object!

4th) THE LHC TUNNEL IN YOUR LIVING ROOM

Although the following object is not very common, it is accessible to anyone who wants to visit it on certain dates when it is open to the public. The LHC (Large Hadron Collider) particle accelerator is the most powerful machine ever built by humans. Located near the Franco-Swiss border, it has a 27 km circular tunnel where proton beams are accelerated to speeds very close to the speed of light. To achieve this, a magnetic field of 8.3 Tesla is needed, and to achieve such an immense magnetic field, the superconducting magnets must be cooled to -271 degrees Celsius. This is almost one degree colder than the temperature of deep space, making this area of the LHC one of the coldest places in the known Universe!

To calculate the distance traveled by relativistic protons, we must resort to Einstein's special relativity. To calculate the Lorentz factor, we use the relativistic energy expression:

E = m0·c2(γ-1)

We know that the energy of the LHC protons is 7 TeV and since the rest mass of the proton is 938.3 MeV/c2 we have that m0 c2 = 9.383 10-4 TeV and therefore 7 TeV = 9.383 10-4 (γ-1). Therefore we have that the Lorentz factor is: γ ~ 7460

Substituting this value in the expression for the relativistic Lorentz factor we have:

γ = 1/[1- (v/c)2]1/2 and therefore the speed of the protons is v = 0.999999991·c

We know from special relativity that a ruler of length Lo traveling at relativistic speeds will see its length contracted by a factor Lo/ γ therefore we have that, for relativistic protons the 27 km of the tunnel becomes: 27km/7460=

0.00362 km. That is, for protons, the 27 km tunnel becomes 3.62 meters! Relativistic contraction means that, from the proton beam reference frame, the LHC tunnel fits in your living room!

(To better understand how these types of apparent relativistic paradoxes are resolved, you can read this article )

5th) THE LIGHT

Finally, we come to the strangest "object" of our everyday lives imaginable: light. This physical entity we call "light," which allows us to see the world around us, behaves in truly strange ways. To begin with, no physical object can ever reach a ray of light in a vacuum . This means that if we emit a photon into empty space, we will never encounter it again. Only objects in the future will be able to detect them. But then, how can we see objects? The answer is surprising: We always see objects as they were in the past. In the case of everyday objects, this effect is completely negligible, but on astronomical scales, we can only observe stars as they were tens, hundreds, or thousands of years ago.

Furthermore, light is the only physical entity for which there is no rest frame of reference. This means that it is impossible to observe a photon at rest, so

It is not possible to assign a mass or time of its own to a photon of light.

We continue with another equally strange characteristic: no one has ever detected a photon "in flight." This means that a photon can only be detected when it is emitted or when it is absorbed by an atom. Certain theories of quantum gravity suggest that the processes of photon emission and absorption are quantumly entangled, although it is still not entirely clear how this fact should be interpreted if it is correct. These and many other unusual phenomena make light a truly special physical entity.

We are so accustomed to the everyday world we see that we don't realize that the physical entity that allows us to see that world is one of the strangest objects in the Universe.

Sources:

Holography, Wikipedia , Relativity, getting closer to the LHC