Why perrin's experiment demonstrates the existence of atoms?

In summary, the stanford encyclopedia of philosophy says that particles are discrete, countable individuals, and that this characteristic alone does not constitute a sufficient condition for being a particle.
  • #1
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Perrin got his nobel prize because of his experiment on brownian motion, which is thought to have proven the existence of atoms

i cannot understand that

if you see an array of dots from STM, i believe you demonstrate the existence of atoms

but i cannot see why perrin's experiment or brownian motion has anything to do with atoms

it cannot be explained without atoms?
 
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  • #2
The tiny specks in the fluid were doing a movement considered a random walk, so something had to be impinging on the specks to cause this motion. Since this something could not be seen with the naked eye or with using lenses, this something had to be very very small. Rather than the fluid being a continious medium down to the infinite, it was determined that matter was composed of tiny particles called atoms or molecules than were still large enough to have momentum enough to have an effect upon the specks.
 
  • #3
256bits said:
The tiny specks in the fluid were doing a movement considered a random walk, so something had to be impinging on the specks to cause this motion. Since this something could not be seen with the naked eye or with using lenses, this something had to be very very small. Rather than the fluid being a continious medium down to the infinite, it was determined that matter was composed of tiny particles called atoms or molecules than were still large enough to have momentum enough to have an effect upon the specks.

this reasoning is not compelling, i would say

the fluid can have fluctuations and give momentum to the specks.
 
  • #4
wdlang said:
this reasoning is not compelling, i would say

the fluid can have fluctuations and give momentum to the specks.

You don't think there were dozens or more scientists that investigated these kinds of possibilities both before the experiment and between then and the award of the Nobel Prize?

Edit: Also, remember that nobel prizes are usually awarded years after the experiments to verify that they are accurate/important.
 
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  • #5
On its own, yes, not very compelling. But Perrin was using his experiment to verify Einstein's equation on Brownian motion. You should realize that this was mainly a conformation of Avogardo's number, and not that there was such a thing as atoms or molecules Even though Perrin's experiment confirmed Einstein's equation ( so they said back then ) his value was out by 20% or so from the accpeted value.
 
  • #6
I'd say the problem is that the story gets simplified to fit in a "sound byte" like "atoms must exist to produce random motions" or some such oversimplified claim. When it gets boiled down that far, you are right to question the conclusion, but the real story is much more complete.

What's really interesting about the story is that for eons, philosophers debated whether a fluid was continuous or atomic in nature, but here Perrin and Einstein are joining forces to basically say, "rather than debate it, let's look at it". A test particle should react differently in the two cases, and that's what they were able to determine, in favor of the atomic model.
 
  • #7
Just because they function like we would perceive a incredibly small concrete particle to function that does not mean that atoms are really incredibly small concrete particles but they could be something else such as a condensed system located within a field that interacts with other condensed systems within the field to give us properties that we typically conceptualize as being physically concrete.

Am I close to what you are attempting to describe?

Anyway I think from the perspective of physics it is not important if they are really physically concrete. It is only important that they function as something that we would perceive as being physically concrete would function.

Ontology of a particle as per the stanford encyclopedia of philosophy below:
Particles are defined as being discrete. Particles are countable individuals in contrast to a liquid or a mass. Obviously this characteristic alone cannot constitute a sufficient condition for being a particle since there are other things which are countable as well without being particles, e.g., money or maxima and minima of the standing wave of a vibrating string. It seems that the so-called primitive thisness or haecceity is missing to make up a sufficient condition for a particle, i.e., it must be possible to say that it is this or that particle which has been counted in order to account for the fundamental difference between ups and downs in a wave pattern and particles (see also the entry on quantum theory: identity and individuality). In Teller 1995 primitive thisness as well as other possible features of the particle concept are discussed in comparison to classical concepts of fields and waves as well as in comparison to the concept of field quanta. A critical discussion of Teller's reasoning can be found in Seibt 2002. There is still another feature which is commonly taken to be pivotal for the particle concept, namely that particles are localizable in space. While it is clear from classical physics already that the requirement of localizability need not refer to point-like localization, it will turn out later in this section that even localizability in an arbitrarily large but still finite region can be a strong condition for quantum particles.
 
  • #8
sorry for the bulk but i also wanted to include this post which details problems associated with a physical interpretation of a particle in a vacuum state:

5.1.1.2 Further Problems for a Particle Interpretation of QFT

The standard definition for the vacuum state |0> is that it is the energy ground state, i.e., the eigenstate of the energy operator with the lowest eigenvalue. It is a notable result in ordinary non-relativistic QM that the ground state energy of e.g., the harmonic oscillator is not zero in contrast to its analogue in classical mechanics. Not only is the same true for the vacuum state in QFT, the relativistic vacuum of QFT displays even more striking features. The expectation values for various quantities do not vanish for the vacuum state. The label ‘|0>’ does not indicate that the energy is zero in the vacuum state. It rather stems from the assumption that there are no particles present in the vacuum state: an N-particle state can be built up from the vacuum state by the N-fold application of a creation operator. Non-vanishing vacuum expectation values prompt the question what it is that has these values or gives rise to them if the vacuum is taken to be the state with no particles present. Since the vacuum state |0> is closely linked to N-particle states where N is not zero, properties of the vacuum state have a great impact on the particle interpretation as such. If particles were the basic objects about which QFT speaks how can it be that there are physical phenomena even if nothing is there according to this very ontology?
 

1. What is Perrin's experiment and how does it demonstrate the existence of atoms?

Perrin's experiment, also known as the oil drop experiment, involved observing the movement of oil droplets in a chamber under the influence of an electric field. The droplets were suspended in air and were found to have discrete, quantized movements, which provided evidence for the existence of atoms.

2. How did Perrin's experiment disprove the continuous theory of matter?

Perrin's experiment discredited the continuous theory of matter, which stated that matter was infinitely divisible, by showing that the movements of the oil droplets were not continuous but rather discrete and quantized. This supported the idea that matter is made up of small, indivisible particles, or atoms, rather than being continuous.

3. What role did Brownian motion play in Perrin's experiment?

Brownian motion, the random movement of particles suspended in a fluid, was a key component of Perrin's experiment. By observing the movement of the oil droplets, Perrin was able to calculate the size and mass of the particles and provide evidence for the existence of atoms.

4. How did Perrin's experiment contribute to the development of the atomic theory?

Perrin's experiment provided strong evidence for the existence of atoms, which was a key component of the atomic theory. It also helped to disprove the continuous theory of matter and solidify the idea that matter is made up of small, indivisible particles. This experiment played a crucial role in the development of the atomic theory.

5. Why is Perrin's experiment still important in modern science?

Perrin's experiment is still relevant in modern science because it provided concrete evidence for the existence of atoms, which is a fundamental concept in chemistry and physics. It also helped to disprove older theories and paved the way for the development of new theories and models. Additionally, the principles used in Perrin's experiment, such as Brownian motion, are still applied in various scientific studies today.

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