Science vs Scientism

 Pure Science is not an ideology; it is a method of examining claims through empirical investigation and then drawing a conclusion that has predictive value. It uses the framework of mathematics and statistics to analyze the evidence, thereby opening up further avenues of investigation to test deeper claims. In this regard, it has been very successful.

Having said that, the Philosopher Paul Feyerabend argues that when the practitioners of science become dogmatic and political in their outlook, they transform the practice of science into a milieu dominated by groupthink. The willful neglect of contrary evidence and the elevation of the power dynamic of credentialism then dominate.

This invariably results in stagnant thinking, the formation of a closed secular priesthood/authority, and the sacrifice of the rigorous scientific methodology to preordained conclusions.

Physics - Modern Physics Phenomena

 

50 Realities that come to us from Modern Physics

(A Second List is coming soon)

• ·         Energy is quantized and  is produced in discrete packets. A quanta of light energy is a Photon. The Energy of a photon is directly proportional to its vibrational frequency. Planck’s constant, h, serves  to turn this proportionality statement into an equation.

  ·         Max Planck’s use of Boltzmann’s Thermodynamics allowed him to solve the Blackbody Radiation Problem. This serves as the origin of Quantum Mechanics.

  ·         Photons have zero mass and travel at the speed c in a vacuum.

  ·          Compton scattering demonstrates that photons have momentum. This is inversely related to their wavelength.

  ·         Traditional particles have wavelike behaviour as demonstrated in the Double Slit Experiment and Electron Diffraction (Davisson-Germer)

  ·         Electrons have spin and angular momentum (Stern-Gerlach)

  ·         Within energy levels electron behaviour can be analyzed using standing wave physics Energy is trapped in the system so that electrons don’t spiral into the nucleus. One can think of an electron as a probability wave.

  ·         Electron orbits are probability functions.

  ·         When electrons move from one energy level to another they release energy in the form of a photon.

  ·         The probability nature of quantum mechanics can be analyzed using wave mechanics (Schrödinger) or matrix mechanics (Heisenberg). Both give verified solutions. One cannot separate statistical mechanics from Quantum Mechanics. Statistical uncertainty is a defining feature of the system.

  ·         There is an inherent uncertainty in Quantum Mechanics which makes perfect certainty on both momentum and particle position impossible on a simultaneous level.

  ·         Anti-Matter is a real phenomenon. Its prediction comes from the work of Paul Dirac and it has been verified at the experimental level. Every particle has an anti-matter adjunct. The positron is the adjunct to the electron. When matter and anti-matter annihilate each other they give rise to Gamma Waves.

  ·         The Macroworld’s continuity breaks down at the quantum level. It can be argued therefore that continuity is an illusion.

  ·         Matter in motion has a wavelength associated with it. (De Broglie wavelength). The utilization of this idea is fundamental to the development of the electron microscope.

  ·         Force transmission occurs through particle exchange.  Feynman diagrams provide an excellent resource to analyze the movement of virtual photons that mediate the Electromagnetic Force.

  ·         There are Four Fundamental Forces in Nature: Strong Nuclear, Weak Nuclear, Electromagnetic Force and Gravity. Although some would argue that gravity is in itself not essentially a force.  They differ considerably with respect to relative strength and range.

  ·         The Strong Nuclear Force holds together the nucleus. It is mediated by Gluons. The Weak Nuclear Force is controlled by the exchange of W and Z Bosons.

  ·         The Graviton is the hypothetical particle thought to be involved in Gravitational interaction. It has not been identified as of the time of writing although Gravity waves appear to be a real phenomenon.

  ·         At high enough temperature it is believed that all four forces were one. These separated very soon after the big bang. At high temperatures for example the electromagnetic force and the weak force merge into one – the Electroweak Force.

  ·         Attempts to bring all of the forces together into a consistent model are part of the idea of Grand Unification. Gravity seems to be the consistent hold out.

  ·         Quantum particles appear to be entangled at some level. This is independent of locality and does not seem to be a function of hidden variables. Its likely a characteristic of the system. Einstein referred to the phenomenon as spooky action at a distance.

  ·         One can treat a quantum entity as either a wave or a particle but never as a wave/particle at the same time (Complementary Principle). Wave particle duality is real.

  ·         In Quantum mechanics the experimenter cannot help but disturb the measurement. This introduces uncertainty as outlined in the Copenhagen interpretation.

  ·         The Photoelectric effect where electrons are ejected from a metal surface by incoming photons can be explained by the threshold frequency of each photon. It is independent of the number of photons irradiating the surface.

  ·         Collapsing the wave function through observation is the key idea behind quantum encryption and eavesdropping shutouts.

  ·         A multitude of quantum states existing at the same time underpins the notion of qubits and Quantum This allows for the system to carry out significantly more calculations (at least in theory)  than conventional computers.

  ·         The Higgs Boson Particle creates a Higgs Boson field that some particles (not photons) can interact with. This gives the particles elementary particles such as quarks and electrons their mass. It was identified by the Large Hadron Collider in 2012.

  ·         The speed of light is constant is equal to c in a vaccum. It is the same for all inertial frames of reference. There is no aether in space. Electromagnetic waves don’t require a medium for propagation.

  ·         One cannot distinguish between the at rest case and constant velocity. The same laws of physics are applicable in both cases. There is no absolute frame of reference to judge motion from.

  ·         Time is a relative not an absolute quantity. It tends on the frame of reference from which it is being determined.

  ·         Space (Length) are relative quantities. The length as perceived by an outside observer contracts in the direction of motion.

  ·         Simultaneity is not absolute. Events that occur simultaneously in one frame of reference aren’t necessarily simultaneous in another.

  ·         Fast moving particles appear to have a substantial increase in linear momentum that  seem to indicate an increase in mass as measured from the frame of the laboratory.

  ·         Space and Time are not independent but can be linked via a spacetime set of axes.

  ·         Protons and Neutrons are composed of three quarks each. There are six quark types. They differ with respect mass, charge and a property called colour. A single quark can have a charge less than the elementary charge. They can transition into each other and do not appear to exist on their own. Quark structures are bound to each other by the Strong Nuclear Force (Guon mediated).

  ·         Electrons, Tau and Muons cannot be broken down into fundamental particles. They are known as leptons and react to the electromagnetic force.

  ·         The Atomic nucleus has various energy levels just like electrons in the outer shells of an atom

  ·         Electron orbits (probability distributions) have various shapes designated s,p, d and f.

  ·         Each of the leptons has an associated neutrino number. Neutrinos are difficult to detect but are not massless. They are produced in nuclear reactions and have no charge.

  ·         The change in apparent half life of fasting Muons passing through the Earth’s evidence is consistent with Time Dilations associated with Special Relativity. Atomic clocks on planes also show time differences that lineup with special relativity.

  ·         Kinetic Energy increases rapidly when a fast moving particle is accelerated toward the speed of light. This is consistent with an increase in relativistic mass.

  ·         Mass and Energy are equivalent and can be related by the equation E= mc². It is more accurate to talk about the conservation of mass-energy as a unit instead of these two terms independently.

  ·         One simply cannot add velocities together in relative velocity problems (like one does in classical physics) but a modified equation that brings in the speed of light limit must be employed.

  ·         For a particle travelling at the speed of light time stands still.

  ·         All information cannot exceed the speed of light in travel speed which makes  c the dividing line between cause and effect.

  ·         The vacuum of space has energy. It is also seething with virtual particles. This has been observed with the Casimir Effect.

  ·         The best model (based on evidence) that we have of the particle nature of the universe is the Standard model – consisting of Hadrons, Bosons and Leptons . However most physics are convinced that there is a layer (or layers) of organization that exist below this.

  ·         The universe may be built on a multiplicity of fields (electrical, magnetic, Higgs, quantum and others) that make all action possible.

  ·         Quantum tunneling allows particles to pass through an energy barrier which would not be possible in the Classical world. This is a function of probability functions arising from the Schrödinger Equation.

  ·         The Conservation Laws in Physics (Energy, Linear Momentum, Angular Momentum etc) can be related to various symmetries via Noether’s Theorem.

   

  
  

Physics Reading List

Books I recommend

1. The Elegant Universe – Brian Greene - excellent introduction into the fundamentals of Modern Physics.

2. Hyperspace – Michio Kaku - wonderful take on extra-dimensions by a strong narrator.
3. The Ideas of Physics – Ernest Hutten - an oldie but a goldie – discusses key ideas that shaped the discipline.
4. Fearful Symmetry – A. Zee - Looks at the Beauty in Physics.
5. Physics of Immortality – Frank Tipler - a bit over the top but highly entertaining nevertheless.
6. Theories of Everything – John Barrow - Low key but well written.
7. Feynman Lecture Series – Richard Feynman - A struggle for the lay person but if you can get through a third of it your effort will be rewarded.
8. The Trouble with Physics – Lee Smolin - an important critique of the group think that has encroached on the discipline.
9. Physics – Douglas Giancoli - Doesn’t matter what the edition is its treatment of classical physics is praiseworthy.
10. The Flying circus of Physics – Jearl Walker – Challenging problems that force one to really think deep.
11. Relativity Simply Explained – Martin Gardiner – Its title says it all.
12. The First Three Minutes – Steven Weinberg- Still one of the best treatments of the Big Bang.
13. The Constants of Nature – John Barrow – Delves into the details of these definitive constants that so encapsulate our universe.
14. Thirty Years that Shook Physics: The Story of Quantum Theory – Gamow is a great storyteller and he didn’t disappoint with this useful read.
15. 50 Physics Ideas – Joanne Baker – Lots of fun and really easy to read.

Why does time slow down the faster you move?

 My Answer on Quora.

It doesn’t slow down at least in the sense that this question is worded. This is a misconception. Lets look a bit more at the bigger picture that comes from Einstein’s Special Theory of Relativity (1905).

Time is a relative concept. There is no such thing as absolute time in the broader scope of non-Galilean relativity. The measurement of time is specific to the frame of reference of the person making the measurement. Within the same frame of reference all observers agree on the same time measurement. However if one frame of reference is moving with respect to the other then there will be a disagreement in how much time has elapsed between events.

You see the only ‘absolute’ here is that the laws of physics hold across all frames of reference. The speed of light in a vacuum as measured by all is the SAME. We call it c. One cannot add or subtract onto c. It is what it is. There is no such thing as c + v or c-v (which Galilean relativity argues for).

Which means that something has to give. Actually several entities do, including absolute time and absolute length. The relative motion of one frame of reference to the other has to be taken into account and it is corrected for by invoking the Lorentz or Gamma factor.

where v = speed of the one frame of reference relative to the other.

For example if Bob boards a space ship and travels at a constant speed v relative to his Earthbound cousin Ann. Bob will experience what is called proper time (a poorly worded term). Ann will be the benefactor of relativistic or measured time. Both measurements of time are correct within their specific frame of reference.

Now the two times are related by the Gamma factor as shown below:

where delta t prime = measured time and delta t is proper time. Gamma is included in this equation and is always greater than or equal to 1. As v approaches c gamma tends to infinity so that the discrepancy between measured time and proper time ramps up considerably. We don’t see this as much in the day-to-day as v is so small compared to c. However the phenomenon is real….we call it TIME DILATION.

Consequently for Ann it will seem that Bob’s clock is running VERY slow. However from Bob’s perspective life is normal and there is nothing wrong with his clock. He will likely argue that Ann’s clock is running too fast. Both are correct in their own frame of reference.

Worth noting is that there is an additional assumption built into this analysis. Both frames of reference are not-accelerating. That is they are Inertial. For accelerating Frames of reference we need to bring in ideas from Einstein’s Theory of General Relativity (1915).

The Mathematical model for Special Relativity in a nutshell

 Special Relativity is predicated on two postulates.

1. All uniform motion is relative and the laws of physics apply equally to all frames of reference.
2. The speed of light is c in a vacuum across all frames of reference.

The necessity of these two paradigms forces a relaxation of absolute time, space, momentum, kinetic energy and simultaneity.

Time Dilation can be understood by a pythagorean analysis of vectors that produces a relation whereby proper time is a multiplied by the Lorentz Factor to obtain relativistic time.

The former is determined by an observer who is at rest relative to the event. The latter sees the event occurring in different places in space.

Relativistic time will always be greater than or equal to measured times with the discrepancy between the two becoming more extreme as velocity tends to c (speed of light).

What are Emprical Laws? How are Newton's Laws Emprical?

 My answer on Quora

These are phenomena that at their very core are driven by the nature of what the universe is at its fundamental level and can only be elucidated through experimentation (not deductive rationalism). They could indeed be otherwise if the nature of the physical universe and its key constants were different. We can probe deeper with mathematics to explain the ‘how’ but the ‘why’ is a different beast altogether.

Newton’s Three Laws of motion emerge as special cases of a broader physics model that rests on a deeper physical base empirically in the MODERN framework. CLASSICALLY without the benefits of Quantum Mechanics and Relativity (both Special and General) we treat them as Empirical.

How were Newton and Huygen's ideas on the nature of light different?

(My answer on Quora)

Both Isaac Newton and Christiaan Huygens were brilliant minds. Where they primarily clashed was on the fundamental nature of light.

Isaac Newton source: World News, Economics and Analysis Based on Bible Prophecy

Christiaan Huygens source: ThoughtCo

Newton believed that light was made up of tint particles called corpuscles that could account for such phenomena as Reflection, Refraction and Rectilinear Propagation.

Huygens favored a wave model where each wave front consisted of wavelets that were the source for the next wave front that propagated forward. Light rays represented the direction of wave propagation.

He believed that all of the properties of light including diffraction could be explained with such a model.

Source: Olympus Science

Huygens Principle and Interference source: Physics Stack Exchange

The deadlock existed until the very early 19th century when Thomas Young carried out his famous Double Slit Experiment. Young was able to produce the characteristic wave interference pattern(alternating bands of maxima and minima) that is the definitive signature for wave like behavior.

Young’s Double Slit Experiment yields definite Interference Pattern source: lumenlearning.com

This implied that in the world of classical physics Huygens was correct - Light is a wave.

In the world of modern physics we now know that light has both a particle and wave nature and exhibits what we called Wave-Particle Duality. Light particles (photons) are however very different to Newton’s original Corpuscles or Billiard balls. 

What does Gibbs Free Energy measure?

 (My answer on Quora).

Gibb’s Free Energy (delta G) measures the maximum amount of reversible work that can be extracted from a system. The caveat though is that the system has to be at constant temperature and pressure (or volume). It must also be a closed system (that is one that does not exchange matter although it can exchange heat and work)

Gibb’s Energy (also known as available energy) is given by the symbol G and is named after the American chemist Josiah Gibbs. The unit of G (like all energies) is Joules (J).

When a system is in chemical equilibrium G is minimized. Delta G becomes zero which implies that no spontaneous energy can be extracted from the system at this pressure and temperature.

Photon Scattering

(Based on my Quora Answer)

A photon is a particle and it doesn’t have mass. It does however have momentum (p).

Source: Hyperphysics

This is shown in the diagram above of Compton Scattering. The collision of the photon with an electron at rest increases the wavelength of the scattered photon and provides the electron with momentum (shown with relativistic correction). Photons have energy that is proportional to its frequency. This energy of a photon can be calculated by multiplying the frequency (v…Greek symbol nu) by Planck’s constant (h).

The momentum of a photon can be calculated by dividing this Energy by c (speed of light in a vacuum).

Remember photons travel at c in a vacuum. Nothing that can travel at c has mass.

In modern physics you don’t need mass to have momentum. In classical physics you do.

Why does the magnitude of acceleration remain constant?

Asked on Quora. My answer.

This happens when the net force is constant (read about Newton’s Second Law of Motion). A free falling object, that is one being impacted by the force of gravity only, is subject to a constant net force that is equal to the weight of the object. (mg). Since the gravity field (g) is roughly uniform close to the Earth’s surface this results in a constant net force and therefore a non-changing acceleration.

In uniform circular motion the magnitude of the acceleration also stays constant if the Centripetal force (another net force) has constant magnitude. However the direction of the acceleration will change though as the net force is perpendicular to the direction of motion of the object which forces a change in velocity but not speed.

Science v Scientism

 Pure Science itself isn’t inherently an ideology. It a method of examining claims through empirical investigation and then drawing conclusion that have predictive value. It uses the framework of mathematics and statistics to analyze the evidence thereby opening up further avenues of investigation to test deeper claims. In this regard it has been very successful.

Having said that though Paul Feyerabend has a point when the practitioners of science become dogmatic and political in their outlook to the point that they transform the practice of science into a milieu dominated by groupthink, the willful neglect of contrary evidence and the elevation of the power dynamic of credentialism.

This invariably results in stagnant thinking, the formation of a closed secretarian priesthood/authority and the sacrifice of the rigorous scientific methodology to preordained conclusions.

The further venture of science into realms which are less quantifiable or indeed falsifiable (eg. morality and metaphysics) further challenges the scope of science’s applicability. A realism that seems lost to those who with each passing moment are intent in transforming science into the ideology of scientism.

Why do gases float? Don't they have gravity?

 (Asked in Quora. My answer)

All gases have weight. Weight is the force of gravity acting on an object and is equal to the mass of the object multiplied by the strength of the gravitational field at the specific point in space.

If you created an imaginary open pathway (or vacuum tunnel) a gas on Earth would be pulled towards the center of the Earth and would travel as such. However such an open pathway only exists in theory. In reality there is material in the way of the gas that is usually more dense than the gas. The material exerts a normal force upwards which pushes the gas backward until it reaches a stable balanced position that we call floating.

We also call this force the buoyancy force and it counteracts the downward pull of the gases weight.

Less dense gases are pushed upward by the buoyancy force provided by the more dense gases below them. These lighter gases will eventually settle in an equilibrium position where the weight pulling down is equal to the buoyancy force pushing up.

Balloons filled with the light gas Helium demonstrate this phenomenon clearly by rising to a level in the atmosphere where the density of gas around then is more rarefied and therefore comparable with the density of the Helium gas itself.

What do Feynman diagrams relate to?

(My answer in Quora).

Feynman Diagrams are very useful visual tools (book keeping devices) that have application in understanding the understanding of particles and antiparticles against the critical back drop of time. They are largely employed in the area of Quantum Field Theory as they offer a mechanism of simplifying a complex system into one that is simpler and easier to understand.

Here is an example of a Feynman Diagram

Particles are shown moving forward in time. Antiparticles are indicated by a backward motion in time.(Source: Physics forum)

In this diagram an electron (e negative) interacts with a positron (e positive), The positron is an antiparticle of the electron so it is shown moving backwards. The two particles annihilate each other producing a photo. The photon is indicated by the -sine wave. This in turn becomes a muon-antimuon pair shown by the Greek letters mu negative and mu plus respectively. Again the antiparticle is shown moving backwards in time.

The interesting story about Feynman diagrams is that they were initially resisted by the physics community who preferred equations/graphs to represent the interactions. To his credit Richard Feynman sold the diagrams to the community where they initially known as Feynman-Dyson diagrams (after Freeman Dyson who made a significant contribution to perturbation theory).

Fun fact…Feynman was not the first person to use these diagrams . The accolade for that for goes to the Swiss Physicist Ernst Stueckelberg. Nobel Laureate Murray Gell-Mann regularly referred to these diagrams as Stueckelberg diagrams in honour of their earlier development.

Key methodology followed when drawing a Feynman diagram

1. Electrons are represented with a straight line in the initial state pointing to a vertex. In the final state they point away from the vertex. Positrons as mentioned earlier are depicted going the other way around.
2. Virtual particles are shown with wavy lines.
3. Exchange particles (such as W + Bosons) are shown with Squiggly lines.
4. Time is shown as going from left to right or bottom to top (depending on the diagram)
5. Gluons - particles that mediate the strong nuclear force are shown as spirals.

The diagrams can take on various complexities that can be analyzed using quantum probability calculations.

source: Research gate.

Below is an example showing how Feynman diagrams are applied in Quantum Field Theory.

Source: IB Physics - Particle Physics/

Further reading

https://arxiv.org/pdf/1602.04182.pdf

What is the closest galaxy to Earth?

 (My answer on Quora).

Earth exists in the Milky Way galaxy whose galactic center is about 0.0265 million light years from us here on the Third Rock. Ironically the Canis Major Dwarf satellite galaxy is 0.0250 million light years from Earth although its classification as a galaxy is disputed.

There are a myriad of satellite galaxies that are very close to the Milky Way (including the Small and Large Magellanic Clouds) but the closest Major galaxy to the Milky Way is Andromeda (M31) which is about 2.5 million light years from Earth. It is a barred spiral galaxy with about twice as many stars as the Milky Way.

Source: D. Karachentsev et al.(2004) A Catalog of Neighboring Galaxies.

Would Maxwell or his contemporaries have known or thought that electricity and electrical phenomenon are made up of transverse waves instead of longitudinal ones prior to his paper that light was a transverse wave?

 My answer on Quora.

Yes they would have. The best evidence that we have that Light is a Transverse wave is that fact that it can be polarized so that the electric field of the EM waves oscillate along one plane. Polarization cannot take place with longitudinal waves such as sound as the transmission direction is the same as that of the disturbance causing the wave. In transverse wave transmission directions are perpendicular to the disturbance and c

Source: Socratic

People have been aware of the phenomena since the age of the Viking. Etienne Louis Malus (1801) showed hope light intensity follows a square drop off law that is related to the angle of rotation between two polarization sheets. Sir David Brewster (1812) further showed how surface reflection at a specific angle (the so-called Brewster angle) can produce polarized light (of use in kaleidoscopes).

The Brewster Angle (Theta B) is the angle of incidence that provides for reflected polarised light Source: This Condensed Life

Western History 169: What were the important developments that occurred in 19th century Chemistry?

As discussed in an earlier answer 18^th century Chemistry could call on such notable figures as Carl Wilhelm Scheele, Henry Cavendish, Antoine Lavoisier, Robert Boyle, Jacques Charles, Joseph Proust  and Alessandro Volta. They set  a high standard for Chemistry as a science. Lavoisier himself is often regarded as the father of Modern Chemistry.

The 19^th century would be even more of a productive period. Englishman John Dalton (1808) , an earlier developer of a periodic table of elements, formulated his law of partial pressures to describe the relationship between components in a gas mixture. He also advanced the notion of multiple proportions.

John Dalton source: Leonardo Newtonic

Swede Jöns Jacob Berzelius (1808) started popularizing the modern use of symbols and notation that we use  today.

Frenchman Joseph Louis Gay-Lussac (1805) showed that water is composed of two parts hydrogen  to one part oxygen and added to the Gas law work carried out by Charles and Boyle in the previous century.

Italian Amedeo Avogadro (1811) proposed the Law that now bears his name in 1811, which states that equal volumes of gas under the same temperature and pressure contain the same number of particles.  The Chemistry concept of the mole (the curse of every high school student), used to define the amount of a substance, follows from his work and was developed later by Johann Lofschmidt (1865).

Amedeo Avogadro with his famous constant (the number of items in a mole of a substance) source: chemistrygod.com

Advances in Organic Chemistry were highlighted by Frederick Wohler’s synthesis of urea  in 1825 (the birth of Organic Chemistry), and his additional endeavours together with Justus von Liebig on Isomers. Both chemists would stress the importance of functional groups in Organic Chemistry as well as the notion of chemical radicals (1832).

Germain Hess in 1840 provided an early version of the concept of Conservation of Energy and this was followed by other advances in physical chemistry around Absolute Zero (Lord Kelvin - 1848), Mass action (Cato Maximilian Goldberg and Peter Wage - 1864), Entropy (Ludwig  Boltzmann - 1877), Chemical Equilibrium shifts (Henri Le Chatelier - 1884), Free Energy (Josiah Gibbs - 1876) and Kinetics (Jacobus van't Hoff- 1884 ).

Hess's Law (named after German Hess - useful in determining energy associated with chemical reactions) source: Socratic

Earlier developments in light spectrometry set in motion the development of analytical chemistry and owe a debt of gratitude to August Beer (1852), Pierre Bouger and Johann  Lambert. Gustav Kirchoff and Robert Bunsen used this technique to discover the elements caesium and rubidium (1859-1860). Similar discoveries from light spectrometery allowed for the identification of iridium, thalium and helium soon afterwards.

Beer's Law (Named after August Beer - shows how the concentration of a solution is related to its light absorbance factor) source: Thoughtco.com

Models highlighting the nature of chemical bonding became more sophisticated in the 19th century. Friedrich August Kekulé (1857) showed how carbon has a tetravalent nature. Soon afterwards Alexandre-Émile Béguyer de Chancourtois (1862), John Newlands (1864) and Julius Lothar Meyer provided earlier versions of the Periodic table (1864). The German Meyer is particularly well known for his organization of the elements around valencies (bonding capacities).

In 1869 Russian Dmitri Mendeleev would publish the First modern Periodic Table containing within it gaps of elements that were awaiting discovery. Much of his efforts were aided by the earlier work of Stanislao Cannizzaro and his organization of the elements by atomic weight in 1860.

Dmitri Mendeleev source: New Scientist

Between 1894-98 Mendeleev’s missing element hypothesis was given credence by William Ramsay’s  discovery of the Noble gases.

Kekulé (1865) also showed how it was possible that Benzene has a six ring carbon structure, ensuring its stability as the base molecular for the Aromatic hydrocarbons. There was a more sophisticated understanding of chemical reactions overall thanks to Alfred Werner’s  work on chemical coordination (1893). Svante Arrhenius ion theory (1883) also helped explain conductivity in electrolytes. 

An early version of the Periodic Table source: Chemistry libre texts

Chemical advances were often driven by the practical needs associated with the industrial revolution. Alexander Parkes' (1862) development of the one of the earliest polymers falls into this category as were the use of dyes (such as indigo) that formed the basis of the work of Adolf von Baeyer (1865) and  William Perkin (mauve - 1856). Benjamin Stillman Jr. was a trendsetter for his ingenuity with respect to petroleum cracking (1855).

William Perkin source: sciencehistory.org

However it is important to note that many chemical breakthroughs were driven by advances in Physics. JJ Thomson’s discovery of the electron in 1897 was one such event and this was followed by Ernest Rutherford and Pierre and Marie Curie’s work on radioactivity. The development of devices such as the Mass Spectrometer by Wilhelm Wien (1898) helped Chemists immensely.