[SOLVED] what is physics ?

[Erdem]

can you make one sentence explanation (definition) for physics.

[ahrkron]

I would say it has at least two one-sentence parts: 1) the search for the smallest set of assumptions that yield correct predictions, and 2) the development of ways to test those predictions.

[StarkyDee]

The science of matter and energy and of interactions between the two, grouped in traditional fields such as acoustics, optics, mechanics, thermodynamics, and electromagnetism, as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics, and plasma physics.

[FZ+]

The search for fundamental law in the universe.

(Hmm, this excludes chaos theory etc... But I can't think of another way that does not include chemistry/biology. Indeed, there may not be a perfect definition.)

[Tom Mattson]

Physics is the study of matter in motion.

Now that I gave you the fortune cookie version, let me expand on that. Since physics is a science, its object of study is the observable universe. Since the universe is not known a priori, it is not really possible to "define" such a subject completely. The definition must change according to the observed results. In this case, I forsee no semantic changes to the definition I gave above, but I do forsee changes in the meaning of the terms contained therein, specifically "motion" and "matter".

In the last century, concept of motion has had to be revised in two different ways. First, there was the relativistic revolution that forced us to put an upper bound on speeds. Second, and nearly concurrently with the first, there was the (much more drastic) quantum revolution that forced us to abandon the concept of forces in dynamics, and to abandon kinematics nearly altogether.

The concept of matter has had to be revised from a solid continuum to an field of atoms which are mostly empty space. As smaller and smaller substructures are discovered, we revise the concept further, even to include such things that would not be considered "matter" in years prior (namely, massless gauge bosons).

We still aren't finished revising these concepts (we never will be), but as I said as far as I can see the definition of "physics" I gave should hold good for the forseeable future, I think.

[cepheid]

I like the definition: the study of the fundamental laws that govern the universe. However, I'm just student. You should listen to the smarter people above. [;)]

[totoro]

this is from my book- the study of the physical world around us.

[Jeebus]

I would just say Physics is the study of physical forces and qualities: the scientific study of matter, energy, force, and motion, and the way they relate to each other. Physics traditionally incorporates mechanics, electromagnetism, optics, and thermodynamics and now includes modern disciplines such as quantum mechanics, relativity, and nuclear physics.

[FUNKER]

============================>Physics is everything<=========================

[suyver]

Everything is physics? [:)]

My shortest definition would be something like: the science that deals with the theoretical understanding, experimental verification and prediction of all fundamental processes that can and may occur in nature.

[FUNKER]

Ok name something any thing and then think to urself is physics involved? Then you'll know my reasoning
[g)]

[Anttech]

Originally posted by FUNKER
Ok name something any thing and then think to urself is physics involved? Then you'll know my reasoning
[g)]

Consciousness...

[Nereid]

Love
Poetry
Sociology
Racism
Zero vs Russ
Dreams
Iosef Stalin
George W Bush

[curlydafatboy]

physics: a branch of science...lol

[WingZero]

lol

[photon]

I think physics is the Greek word for nature.

[Carla1]

Originally posted by Tom

In the last century, concept of motion has had to be revised in two different ways. First, there was the relativistic revolution that forced us to put an upper bound on speeds. Second, and nearly concurrently with the first, there was the (much more drastic) quantum revolution that forced us to abandon the concept of forces in dynamics, and to abandon kinematics nearly altogether.




Hiya Tom...hope things go well your way.

How did the quantum revolution force physicists (such ironic terms) to abandon the concept of forces in dynamics, and kinematics for that ...oh god I cant help myself...matter? :P

While I'm attit...what's all this wave and geodisics business about?

You usually state things simply and with clarity so I look forward to more of the same.

[Tom Mattson]

Originally posted by Carla1
Hiya Tom...hope things go well your way.


Yes, they are going well. Busy though--my students are going crazy with finals.

I'm guessing that you are our long-missing, beloved Carla. Why the name change?


How did the quantum revolution force physicists (such ironic terms) to abandon the concept of forces in dynamics, and kinematics for that ...oh god I cant help myself...matter? :P


Classical dynamics as a variety of equivalent formulations. On the one hand, there is Newtonian dynamics which is in terms of forces. On the other hand, there are Lagrangian and Hamiltonian dynamics, which are in terms of energies. It turns out that quantum mechaincs is modeled on the latter, and it seems that it cannot be modeled on the former. At least, no one seems to be able to think of a way to to it (we discussed this briefly in another thread I started called "Quantizing Newton", which you can find in the Archives if you are so inclined).

So, quantum mechanics is formulated in terms of energies (modeled on Hamiltonian dynamics), and the impetus of motion for particles is not a force, but a potential energy function. The next step is quantum field theory, which abandons the potential energy function in favor of a quantized interaction. In the case of the electromagnetic interaction, it is quantized into virtual photons.

As far as kinematics goes, that is a geometric description of the motion of a particle without regard for the impetus that gave rise to the motion. It is formulated in terms of the trajectory of a particle, x(t). If we take the time derivatives, we get v(t) and a(t) for the velocity and acceleration, respectively. This allows us to simultaneously calculate the position and the momentum of the particle, p(t)=mv(t), where m is the mass. But quantum mechanics tells us that it is not possible to specify both x and p. So, kinematics is out the window. (We can, however, do "kinematics" on the expecation values of the position and momentum operators, but that is another story).




While I'm attit...what's all this wave and geodisics business about?


I guess you'll have to be more specific about these. Quantum Mechanics is also called "wave mechanics" because it describes matter with a wave equation, and geodesics are straight lines in curved spacetime. Massless particles always follow geodesics.

[Carla1]

Originally posted by Tom
Yes, they are going well. Busy though--my students are going crazy with finals.

I'm guessing that you are our long-missing, beloved Carla. Why the name change?



Classical dynamics as a variety of equivalent formulations. On the one hand, there is Newtonian dynamics which is in terms of forces. On the other hand, there are Lagrangian and Hamiltonian dynamics, which are in terms of energies. It turns out that quantum mechaincs is modeled on the latter, and it seems that it cannot be modeled on the former. At least, no one seems to be able to think of a way to to it (we discussed this briefly in another thread I started called "Quantizing Newton", which you can find in the Archives if you are so inclined).

So, quantum mechanics is formulated in terms of energies (modeled on Hamiltonian dynamics), and the impetus of motion for particles is not a force, but a potential energy function. The next step is quantum field theory, which abandons the potential energy function in favor of a quantized interaction. In the case of the electromagnetic interaction, it is quantized into virtual photons.

As far as kinematics goes, that is a geometric description of the motion of a particle without regard for the impetus that gave rise to the motion. It is formulated in terms of the trajectory of a particle, x(t). If we take the time derivatives, we get v(t) and a(t) for the velocity and acceleration, respectively. This allows us to simultaneously calculate the position and the momentum of the particle, p(t)=mv(t), where m is the mass. But quantum mechanics tells us that it is not possible to specify both x and p. So, kinematics is out the window. (We can, however, do "kinematics" on the expecation values of the position and momentum operators, but that is another story).





I guess you'll have to be more specific about these. Quantum Mechanics is also called "wave mechanics" because it describes matter with a wave equation, and geodesics are straight lines in curved spacetime. Massless particles always follow geodesics.


Mmmk. I am going to have to run this past you again kind of dialectically. I hope this is not too boring a process for you, though. And I changed my name slightly because I have changed my ISP so I can not get in as a registered member under 'Carla' thus I re-registered as Carla1 under my new Em-address. Beloved, hrrm, I detect sarcasm, oh mischievous one.

When you use the term 'quantum', I understand this to be a term meaning the measurement of very small quantities in nature. That is, the operation of the mechanics of things at their most basic level. Force I understand as being impetus of motion or change. Energy I understand as being power, potential as inert power. Particles are the 'little bits' you attempt to measure which tend to elude by also acting as waves under certain conditions. One such particle is a photon. I'm really lost on field theory but does the following bear any resemblence : field theory is how particles/waves interact relative to certain conditions or 'fields' within which they operate?

Why is the term 'virtual photons' used instead of photons?
What is meant by 'wave'...is this a frequency or how particles move through 'space'?

And here's an easy one...how do space and time fit together? And how can they be curved?

Appreciation to be continued...

[Achy47]

Personally I find those types of questions difficult and recursive when I think too hard about them.
However this one reminds me of a quote made by Einstein:

"If we knew what it was we were doing, it would not be called research, would it?" [:))]

[Carla1]

I was seeking generally accepted definitions of these things in the world of physicists. I understand it's an ongoing process. No pressure to come up with THE definitive, undisputed truth-of-the-matter...

I'll ask that next week. [6)] [;)]