Modern Physics is Fundamentally Different from Classical Physics

Superfact 144: Modern Physics including Quantum Physics and Relativity is fundamentally different from Classical Physics. Even if you include Relativity in Classical Physics, which is often done, it is still fundamentally different from “Classic Classical Physics”.

Esther’s writing prompt: October 28th: Classic

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An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case.
Electrons (and other particles) don’t have specific positions. They are probability clouds. This is an illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The black bar is one angstrom (10−10 m or 100 pm). The nucleus is 0.01pm. User: Yzmo, CC BY-SA 3.0, via Wikimedia Commons.

Classical physics and modern physics represent two major phases in our understanding of how the universe works. Classical physics includes fields such as classical mechanics, electromagnetism, optics, and thermodynamics. Modern physics include relativity and quantum mechanics. However, relativity is often said to be classical physics as well as modern physics.

In classical physics time and space are independent of the observers, objects can have exact positions and velocities, and if you measure them precisely you can make exact predictions. Furthermore, energy and matter are continuous. In relativity time and space are relative, and there is no universal now. The order of events depends on the observer and energy and mass are interchangeable. In quantum physics particles do not have a specific positions or velocities, they behave as both particles and waves, and energy is quantized. In quantum physics you have probabilities instead of certainties. The electrons (and other particles) in atoms are described as probability clouds (see picture above). Classical physics and modern physics are very different.

The picture shows three pairs of lamps and three people. The setup is used to show three situations.
Amy is traveling at a high speed to the left compared to two lamps A and B. Alan is standing still compared to the lamps. Adam is traveling at a high speed to the right compared to two lamps A and B. Alan turns on the lamps at the same time. After considering the travel time of the light she sees, Amy concludes that lamp B turned on first. After considering the travel time of the light he sees, Adam concludes that lamp A turned on first. I should add this non-simultaneity can only happen if the lamps are separated by a distance.

A famous but simple formula from quantum mechanics is the Heisenberg uncertainty principle which states that you cannot both know the exact position and momentum (that is mass times velocity) of a particle. Another version of it states that you cannot both know the exact energy and the time interval to measure it. Basically, it is impossible to know a particle’s quantities exactly. They don’t even exist other than as probabilities.

The picture shows the formula for the Heisenberg uncertainty principle
Heisenberg uncertainty principle Shutter Stock Vector ID: 2380436193 by Sasha701

The difference between how things work in classical physics and in modern physics is very large. The language and philosophy of classical physics and modern physics is not even the same. I believe that the fact that there is such a large and distinct difference between the two phases of physics comes as a big surprise to those who were unaware of it. Since this fact is important and potentially surprising, perhaps mind-blowing, it is a super fact in my opinion.

It is easy to think that modern physics is philosophical, mysterious, esoteric, and impractical. It is not. Pretty much all of the electronics you have ever used exist because of modern physics. Modern physics is also essential for lasers, MRI and PET scans, modern medicine, nuclear power, nuclear weapons, GPS, atomic clocks, solar power, small-scale nanotechnology, and a large amount of new materials. That might be a super fact all in itself.

Special Relativity

Relativity comes in two flavors, special relativity and general relativity both pioneered by the physicist Albert Einstein. Special relativity states that the speed of light in vacuum is a universal constant c = 299,792,458 meters per second. The speed of light in vacuum is the same for all observers regardless of their speed and the direction in which they are going. It is always c = 299,792,458 meters per second. If you try to catch up to a light beam and try to travel close to the speed of the light beam, you will not be able to catch up. The speed of the light beam will still be c = 299,792,458 meters per second compared to you no matter how fast you go. In fact, anything without (rest) mass will travel at exactly this speed compared to everything else, whilst nothing else could ever reach or exceed this speed.

A spaceship on the right is shooting out a laser beam towards the left. Alongside the laser beam are four rockets trying to catch up with the light beam.
Four rockets, A, B, C, and D, are traveling along a light (laser) beam. No matter how fast they travel along the light beam, the light beam will always travel c = 299,792,458 meters per second faster than they do. I generated this picture with the help of ChatGPT.

Some consequences of this is that there is no universal now, two events may be simultaneous for some but not for others, two observers moving compared to each other will both observe the other’s time as being slower, and energy and mass are interchangeable, and time acts like a fourth dimension.

The E = mc2 formula
Mass is energy and vice versa, a direct result of the way time and space are related. Stock Photo ID: 2163111377 by Aree_S
The image shows the formulas for the spacetime interval with the constant representing the speed of light in vacuum “(s^{2}=x^{2}+y^{2}+z^{2}+(ict)^{2}”, “s^{2}= (ct)^{2} – (x^{2}+y^{2}+z^{2})” and “(s^{2}=x^{2}+y^{2}+z^{2}-(ct)^{2}”.
If you measure the space coordinates in meters and the time in seconds you must adjust the units to match by inserting the speed of light in vacuum c = 299,792,458. The three forms of the space interval now have the constant c attached to the time coordinate.

General Relativity

In General Relativity gravity is not viewed as a force over distance. Mass / energy is distorting the local space-time creating the effects of gravity. Even though the end result is very similar to Newton’s theory of gravity, the General Theory of Relativity is much more accurate. The General Theory of Relativity also predicts that clocks will be running slower in gravitational fields. It predicts gravity waves, and the strange behavior of black holes, and it is necessary for GPS to work.

The picture shows planet Earth in the middle surrounded by a bent grid with Earth in a gravity well.
Earth is a mass that distorts space-time resulting in what we call gravity.
A black hole with a large bright accretion disk.
3D illustration of giant Black hole in deep space. High quality digital space art in 5K – realistic visualization. Stock Illustration ID: 2476711459 by Vadim Sadovski.

Quantum Physics

As mentioned, in quantum physics, particles do not have specific positions or velocities. See the Heisenberg uncertainty principle above. In quantum physics you have probabilities instead of certainties, and energy is quantized. The electrons (and other particles) in atoms are described as probability clouds. Particles behave as both particles and waves, the so called wave particle duality. Particles exhibit both wave-like and particle-like properties depending on the type of measurement. An example is the famous double slit experiment.

If you shoot electrons, or any particle, through a double slit (panel with two slits) they will show up on the detector panel behind the first panel as if they were a wave. There will be interference patterns (multiple bands), the same as you would get from light waves or water waves. You will even get the interference pattern if you shoot the electrons one by one. However, if you try to detect the individual electrons to see which slit they went through you will get just two bands as if the electrons were bullets going through the slits. In other words, if you look at them, they won’t do the beautiful interference pattern anymore, as if they are saying, “if you look at me, I won’t do it”.

The experimental setup is an electron gun on the left. Electrons are shot towards a panel with two slits. Behind that panel is another panel which displays an interference pattern with multiple bands.
Photons or matter (like electrons) produce an interference pattern with multiple bands when two slits are used. Original: NekoJaNekoJa Vector: Johannes Kalliauer, CC BY-SA 4.0, via Wikimedia Commons.

One amazing discovery was that of anti-particles / anti-matter. Anti-matter was predicted in 1928 by the physicist Paul Dirac when he combined quantum mechanics with Albert Einstein’s special theory of relativity. A few years later (1932) the anti-particle of the electron, called the positron was discovered. Since then, many anti-particles have been found. I can add that Matter and anti-matter annihilate upon contact releasing enormous amounts of energy.

The pictures show a positron and an electron merging in an explosion with a wavelike photon emerging on the right.
Annihilation of a positron (at the top left) and an electron (bottom left) with the release of energy and gamma quanta Shutterstock asset id: 2200151693 by Sergey Merkulov

Conclusion

Going from classical physics to modern physics represented a huge quantum leap forward (pun intended) both with respect to our understanding of the Universe and the technological revolution this shift (paradigm shift) caused.

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Author: thomasstigwikman

My name is Thomas Wikman. I am a software/robotics engineer with a background in physics. I am currently retired. I took early retirement. I am a dog lover, and especially a Leonberger lover, a home brewer, craft beer enthusiast, I’m learning French, and I am an avid reader. I live in Dallas, Texas, but I am originally from Sweden. I am married to Claudia, and we have three children. I have two blogs. The first feature the crazy adventures of our Leonberger Le Bronco von der Löwenhöhle as well as information on Leonbergers. The second blog, superfactful, feature information and facts I think are very interesting. With this blog I would like to create a list of facts that are accepted as true among the experts of the field and yet disputed amongst the public or highly surprising. These facts are special and in lieu of a better word I call them super-facts.

One thought on “Modern Physics is Fundamentally Different from Classical Physics”

  1. That’s really fascinating, especially about the double slit experiment, that really caught my imagination. I didn’t know there were such differences between classical and modern physics. For a subject that I’m not knowledgable about, you’ve made it accessible. Thanks for educating.

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