Do we actually know what energy or matter fundamentally is?  Is it even possible to know?

How would you know that you have reached the fundamental level. How would we even know that any theory can describe nature exactly. I don't think it is possible to know. The history of science should be sufficient warning that nature always has more subtlety and new surprises in store.

Energy is, at the end of the day, a concept we ourselves have developed to describe certain aspects of nature. It is a number (one of many) we can assign to states of matter and radiation, which is particularly useful for describing physical processes because it 1) remains the same to good accuracy, 2) tells us how strongly an object is involved with gravitation, 4) and knowing how this number depends on the detailed configuration of particles and fields yields precise predictions about its future movements, a indispensable approach to physics pioneered by people like Hamilton and Lagrange. 5) Its flow is related to Entropy

Because total Energy stays the same and energy transfer at a certain temperature gives the change in Entropy, we can easily tell whether certain work can be accomplished by a physical system simply by looking at how much energy it contains, how much of it must be transferred to accomplish the task, and whether the entropy of the system is low enough such that this transfer will occur without clashing with the second law. Other conserved quantities such as angular Momentum and Momentum can give similar useful information, but Energy tends to be the most powerful concept.

It is a philosophical can of worms unto itself whether Energy is something that fundamentally exists in nature, or whether it is just an effective description of nature. I have given a modern and very general definition of what energy is in a different thread: it can be identified with the conserved quantity which is associated with a particular continuous symmetry in the laws of nature, namely that the laws of nature do not vary over time.

If time stops to be a continuous thing when looking closely enough because it becomes fuzzy or discrete at short enough time intervals, it will become difficult to even find a fundamental definition of what Energy is, and the concept of Energy might just be describing an emergent property of physical systems (like air pressure or temperature) that is not really a fundamental property of stuff but instead something that only appears when looking at large averages of particles or, in this case, many Planck time intervals or what have you.

(March 14, 2016 at 6:46 am)Alex K Wrote: If time stops to be a continuous thing when looking closely enough because it becomes fuzzy or discrete at short enough time intervals, it will become difficult to even find a fundamental definition of what Energy is, and the concept of Energy might just be describing an emergent property of physical systems (like air pressure or temperature) that is not really a fundamental property of stuff but instead something that only appears when looking at large averages of particles or, in this case, many Planck time intervals or what have you.

Are there any examples of when time intervals may become that short besides perhaps very near the initial event of the Big Bang?

(March 14, 2016 at 7:32 am)Panatheist Wrote:

(March 14, 2016 at 6:46 am)Alex K Wrote: If time stops to be a continuous thing when looking closely enough because it becomes fuzzy or discrete at short enough time intervals, it will become difficult to even find a fundamental definition of what Energy is, and the concept of Energy might just be describing an emergent property of physical systems (like air pressure or temperature) that is not really a fundamental property of stuff but instead something that only appears when looking at large averages of particles or, in this case, many Planck time intervals or what have you.

Are there any examples of when time intervals may become that short besides perhaps very near the initial event of the Big Bang?

It's not a question of time intervals becoming short (whatever that should mean), it's a question of how short time intervals we want to describe with our theories. No need to go to the big bang. You can, at least hypothetically, ask the question how e.g. a particle reaction today proceeds between time "t" and time "t + planck time". If the difference in time you study is small enough, you run into this conceptual problem. For the description of everyday physics, the detailed goings-on between such short time steps might not be relevant because they average out, but since you ask the question about the *fundamental* nature of energy, you require us to consider nature at arbitrary, nay, infinite, precision and see whether we can still describe it - that's what the demand for a truly fundamental picture entails.

At the LHC, we are trying to move closer towards this unattainable goal: using higher and higher energy collisions, one can probe the laws of nature at ever shorter time scales because the collision energy is directly proportional to the frequency of the particle waves. However, the LHC does not reach near Energies where Planck time processes can be resolved. That's why it is a hypothetical endeavour for now to think about the breakdown of the concept of a continuous timeline.

Still, if you want to theoretically describe ever smaller steps in the evolution of a physical system, you run up against this barrier of Planck-Time steps, and that tells you that the *fundamental* description of nature might be more complicated than just having time flow continuously.

(March 14, 2016 at 7:53 am)Alex K Wrote:

(March 14, 2016 at 7:32 am)Panatheist Wrote: Are there any examples of when time intervals may become that short besides perhaps very near the initial event of the Big Bang?

It's not a question of time intervals becoming short (whatever that should mean). No need to go to the big bang, you can, at least hypothetically, ask the question how e.g. a particle reaction today proceeds between time "t" and time "t + planck time". If the difference in time you study is small enough, you run into this conceptual problem. For the description of everyday physics, the detailed goings-on at such short time steps might not be relevant because they average out, but since you ask the question about the *fundamental* nature of energy, you require us to consider nature to arbitrary, nay, infinite, precision and see whether we can still describe it - that's what the demand for a truly fundamental picture entails.

At the LHC, we are trying to move closer towards this unattainable goal: using higher and higher energy collisions, one can probe the laws of nature at ever shorter time scales because the collision energy is directly proportional to the frequency of the particle waves. However, the LHC does not reach near Energies where Planck time processes can be resolved. That's why it is a hypothetical endeavour for now to think about the breakdown of the concept of a continuous timeline.

Still, if you want to theoretically describe ever smaller steps in the evolution of a physical system, you run up against this barrier of Planck-Time steps, and that tells you that the *fundamental* description of nature might be more complicated than just having time flow continuously.

Okay, I cannot understand most of this, but I'm getting a glimpse of what I'm asking about.  Does what you say here also imply that the supposed linear nature of time also breaks down at very short time intervals?  (Does it make sense to ask if a segment of time is infinitely divisible?)

(March 14, 2016 at 8:02 am)Panatheist Wrote:

(March 14, 2016 at 7:53 am)Alex K Wrote: It's not a question of time intervals becoming short (whatever that should mean). No need to go to the big bang, you can, at least hypothetically, ask the question how e.g. a particle reaction today proceeds between time "t" and time "t + planck time". If the difference in time you study is small enough, you run into this conceptual problem. For the description of everyday physics, the detailed goings-on at such short time steps might not be relevant because they average out, but since you ask the question about the *fundamental* nature of energy, you require us to consider nature to arbitrary, nay, infinite, precision and see whether we can still describe it - that's what the demand for a truly fundamental picture entails.

At the LHC, we are trying to move closer towards this unattainable goal: using higher and higher energy collisions, one can probe the laws of nature at ever shorter time scales because the collision energy is directly proportional to the frequency of the particle waves. However, the LHC does not reach near Energies where Planck time processes can be resolved. That's why it is a hypothetical endeavour for now to think about the breakdown of the concept of a continuous timeline.

Still, if you want to theoretically describe ever smaller steps in the evolution of a physical system, you run up against this barrier of Planck-Time steps, and that tells you that the *fundamental* description of nature might be more complicated than just having time flow continuously.

Okay, I cannot understand most of this, but I'm getting a glimpse of what I'm asking about.  Does what you say here also imply that the supposed linear nature of time also breaks down at very short time intervals?  (Does it make sense to ask if a segment of time is infinitely divisible?)

I think it makes sense, and the linear nature of time might indeed break down. People who deal with this problem explicitely are working in Loop Quantum Gravity research. They construct spacetime as basically a network of discrete nodes giving rise to the famous "quantum foam" concept of spacetime. They have a real hard time properly defining what time is!

Maybe it helps to look at something familiar to get the general idea. A water wave is a continuous thing if you look at it at human scales, characterized by the distance between its troughs and peaks, and how high the peaks are, but if you look closer and closer, you find that it is made up of discrete atoms binding together in complicated ways, evaporating, mixing, etc. The fundamental description of a water wave when you zoom into it far enough suddenly involves very different ideas than the concepts you use to describe water from a macroscopic human perspective. The same could happen with time when we zoom in to look what happens in super short time steps.

As for matter, we really don't have 'pure' matter to do experiments on and to study. The stuff we have and think of as 'matter' is actually a hybrid substance consisting of 40% energy (m/l) and 60% matter.

Maybe we can't handle the real thing ?

Wow, so much nonsense in this thread, I wouldn't know where to start...

(March 14, 2016 at 9:37 am)little_monkey Wrote: Wow, so much nonsense in this thread, I wouldn't know where to start...

Do you disapprove of something I said?

If it makes sense to say time is infinitely divisible doesn't that imply that it isn't linear? Could that be an argument for a Block-Space universe (eternalism)?