Ask any question you want about Physics

originally posted by: Arbitrageur

originally posted by: Bedlam
As a sort-of example, consider lightning. Once the strike causes air expansion along the channel, creating a thunder clap, the event is over. Yet, miles away, you will hear the boom.

Great point. This made me think of the more dramatic example of the 2004 Earthquake which lasted about 10 minutes, but after that stopped, the tsunami wave kept propagating for at least 7 hours to distant shores.

a reply to: dragonridr
I found this quote from Dyson that pretty much confirms he's never worked on string theory:

www.math.columbia.edu...

I would like to say a few words about string theory. Few words, because I know very little about string theory. I never took the trouble to learn the subject or to work on it myself.

I didnt think he did?? its a little after his his time. But as i explained in earlier post fields never have a zero energy total at any point in space but something created them. If he believes fields created the universe hes an early string theorist he just didnt know it. QFT doesnt have anything about fields creating everything we see only the interactions. Only thing close to that is the crackpot primer fields i read one time and that isnt QFT.

Of course if you have a paper on QFT that says matter was created with fields and they exist without being created send it my way i all ways like to read new stuff.

originally posted by: dragonridr
I didnt think he did?? its a little after his his time.

It wasn't my intention to bring up string theory, you're the one who brought it up here:

originally posted by: dragonridr
This involves string theory an imbalance was created causing a symmetry imbalance at the cteation of the universe. I for one am not a fan of string theory

I read his comments on string theory and I don't think he's any more of a string theory fan than you or me, though he has worked side-by-side with some string theorists so he's trying to be somewhat diplomatic toward them.

But to recap how this got started, Imafungi said something about omnipresent fields, and you pointed out that the fields aren't really everywhere. Then you finally clarified that yes they are but with diminished intensity the further you get from matter, so with that, the initial apparent discrepancy of ImaFungi saying there were fields everywhere contrasted with your statement that:

An incomplete understanding and you end up spinning circles and thinking there is some field everywhere in space. There isnt fields are created they are not preexisting.

which you later clarified that there are in fact fields everywhere in space (I think).

Regarding the nature of vacuum fields, they aren't well understood and I'm pretty sure you know all this. We have the vacuum catastrophe on the theoretical side, but on the observation/experiment side we have dark energy, which doesn't appear to be consistent with your observation here:

originally posted by: dragonridr
In practice, the strength of most fields has been found to diminish with distance to the point of being undetectable.

That statement is obviously true with respect to some fields, but it is also true in the implication of "most fields" that it doesn't apply to all fields, with dark energy, possibly being vacuum energy, appearing to not follow this concept since it appears to be fairly uniform regardless of its proximity to matter, at least as far as our crudest observations to date have suggested. More refined measurements in the future may paint a different picture.

But as i explained in earlier post fields never have a zero energy total at any point in space but something created them.

This may be largely true, however regarding dark energy/vacuum energy related to the accelerating expansion of the universe, I don't think we know what created those fields, if it can even be explained by quantum field theory which the present vacuum catastrophe suggests maybe it can't, at least not without some changes, right?

a reply to: Arbitrageur

Well vacuum energy isnt a field just keep in mind any energy will create a field virtual or not. We could argue for example a higss field is everywhere. But at the same time its no where because in order to see the virtual particles it has to interact with non virtual particles causing a field. Like the higs boson is associated with a scalar field as im sure you know a scalar field is a point in space with a non zero value. When looking at it from QFT it will exist everywhere because we cant have a zero value no matter how far we get from the source. The math wont allow it though it can be so small that there is no way to detect it of course. But in the statement he made he seemed to say everything was created by fields this is a key element of string theory since ultimately are vibrating strings create fields these fields create particles and of course particles create matter.

So the more i think about it he must at least believe in the possibilities of strings even if he wasnt fond of it. Me of course im just not convinced when you need 11 dimensions just to get it to work and than still when it doesnt than come up with hundreds of variations i dont think the idea is very solid. Not to mention we havnt nor i believe can we in any way make a prediction with it since there to busy trying to fit it in to what we already know.

originally posted by: dragonridr
Well vacuum energy isnt a field

I'm not sure why you say "a field" as in singular. The quote from Dyson referenced "ten to twenty" fields, and I believe he is talking about quantum field theory. I'm not quite sure exactly what part of his comments make you think it's string theory, but his comments seem consistent with what I know of quantum field theory.
Dyson's comments seemed to reflect this observation about quantum field theory in the vacuum:

Vacuum Energy

Quantum field theory states that all fundamental fields, such as the electromagnetic field, must be quantized at each and every point in space.

...Excitations of the field correspond to the elementary particles of particle physics. Thus, according to the theory, even the vacuum has a vastly complex structure and all calculations of quantum field theory must be made in relation to this model of the vacuum.

So, Dyson is referring to these "excitations of the field", not "vibrating strings", though I suppose a string theorist may say they are vibrating strings, but that's not what Dyson is saying as far as I can tell.

When looking at it from QFT it will exist everywhere because we cant have a zero value no matter how far we get from the source. The math wont allow it though it can be so small that there is no way to detect it of course. But in the statement he made he seemed to say everything was created by fields this is a key element of string theory since ultimately are vibrating strings create fields these fields create particles and of course particles create matter.

"Excitations of the field correspond to the elementary particles of particle physics"...That's from the quote above about Quantum field theory. Now as I said some people have tried to infer a relationship between QFT and string theory, but I think you can say "Excitations of the field correspond to the elementary particles of particle physics" without being a string theorist, can't you? That's how I understood Dyson's comments, in that context.

So the more i think about it he must at least believe in the possibilities of strings even if he wasnt fond of it. Me of course im just not convinced when you need 11 dimensions just to get it to work and than still when it doesnt than come up with hundreds of variations i dont think the idea is very solid.

No I don't think he's very fond of string theory based on his comments and he may not believe in the 11 dimensions either.

Now back to this "because we cant have a zero value no matter how far we get from the source." I agreed that does apply to some fields. But do you agree that dark energy seems to be relatively uniform regardless of distance from the "source" if we are to infer that the source is some kind of matter? I don't know if it's the result of fields or not but that's one idea and if it is, then those fields (or whatever creates dark energy) appear to still be present in immense voids far from any source, according to all the interpretations of dark energy data I've seen.

I don't think we understand vacuum energy well and quantum field theory fails to agree with observations of dark energy if it's the same thing as vacuum energy which many seem to think, so without some tweaking, it's apparently not the correct model for calculating vacuum energy, and we don't have a better one to my knowledge. It's a gap in our understanding.

originally posted by: ErosA433
a reply to: ImaFungi

I think much of this post doesn't make concise sense. You pose many many assumptions and ask questions that are either not questions, or at questions at the end of elaborate thought experiments.

You say you are interested in what exists in reality and yet at the same time you are wanting to describe something fundamental without even looking at or considering what we know already as a means to that end.

No, no. I know exactly what I was asking, please attempt to answer my very concisely sensical questions.

a reply to: Arbitrageur

I agee the nature of vacuum energy is a mastery. But any energy will create a field of some kind doesnt mean its pre existing at least not in my book.

a reply to: ImaFungi

In your case if i didnt answer the question i guess you need to rephrase it because o thought i already answered it.

a reply to: dragonridr
Yes we agree vacuum energy is a mystery but if you're saying that it's not "pre-existing", then perhaps I don't understand your concept of "pre-existing" in that context.

I do understand it in the context of say, a moving electron bringing its electric charge into a volume of space where previously there was no electron.

a reply to: ImaFungi

It would appear to me that we have very different views on the meaning of the words concise and sensical.

None of the post was concise, the questions where not clearly asked, the questions where asked mid way through several thought experiments that you actually wrote half way, stopped, and wrote in a different way.

Sorry, We are not purposely ignoring your questions. It is, for me at least. Not possible to go down an elaborate thought experiment when you appear to invent rules and assume things along the way in order to steer an apparent open question into being a Rhetorical question that you already have assumed an answer for.

Lets say we have x, and it does y, then is it true that z should happen?

Is the simplest logical summary of many of your questions and let me break it down as follows...

If i know that when we have x, that it never does y, then z is irrelevant.

This is the basic answer to many of your questions. The reason for this is because you have missed or ignored things that have been said to you. It sounds very much like these big elaborate theories people come out with, but you see that the first assumption or first stipulation is none physical and is either wrong, or there is zero evidence for... and yet there is a compounded level of assumption which the author just cannot accept as being a problem....

a reply to: ErosA433

No. Quote my questions, read them slowly, and attempt to answer them. You will be surprised at how they are the perfect questions to ask, when one is curious about the most fundamental nature of reality. If you do not attempt to answer at least one of them, if you cannot read through, and catch the over all drift of where I am getting at with one line of questions or another, then this is not my fault, I have asked I would guess at least 10 questions in that reply that you are not answering,, read slowly, I was very thorough.

a reply to: ImaFungi
If you ever read any of the ATS "Ask me anything" threads, posters are asked to limit questions to one per post. I imposed no such rule in this thread, however, it's not a bad idea, and you might have better luck getting an answer to one concise question, than a whole barrage of questions buried in a long rambling post, which I hope you will admit was not concisely worded. I honestly thought you were joking about that post being concise; do you mean you weren't joking about it being concise? Do you know what concise means?

originally posted by: Arbitrageur
a reply to: ImaFungi
If you ever read any of the ATS "Ask me anything" threads, posters are asked to limit questions to one per post. I imposed no such rule in this thread, however, it's not a bad idea, and you might have better luck getting an answer to one concise question, than a whole barrage of questions buried in a long rambling post, which I hope you will admit was not concisely worded. I honestly thought you were joking about that post being concise; do you mean you weren't joking about it being concise? Do you know what concise means?

Nothing you said above matters. I made a long post with lots of questions. It is asking about the nature of electrons and EM radiation. The questions are right there, if someone thinks they know about the fundamental nature of electrons and EM radiation, they would read that post I made, and attempt to answer the questions. I follow a train of thought, quote parts of that post that you dont understand and I will make my questions more concise.

A vehicle moves forward in space because of a thrust expelled form on end. The vehicle moves in the opposing direction of the thrust. Why does the vehicle move at all if the particles expelled from the opposite end aren't reacting with anything? The vehicle and its thrust are a closed system. According to the law stated below, an external force must be present for the vehicle to move.

Newton's third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

What force is being exerted on the vehicle body to make it move?

I will try to answer my own question. It must be the pressure difference between the two ends of the nozzle the thrust is coming from. High pressure on one side of the nozzle and low pressure on the otherside.

I am on a roll here.

It has been postulated that everything falls at the same speed. This was shown as one of the first moon experiments when a wrench and feather were dropped at the same time. They hit the Moon's surface at the same time. I say that objects don't fall at the same speed.

If the force of gravity is greater than the force that is holding a mass together than the mass will have a slower fall rate. In a very high force of gravity environment masses will fall at a slower rate than masses in a lower gravity environment. In a extremely high gravitational field a mass would be repelled rather than attracted or would be ripped apart and scattered as energy not falling into the black hole.


Numerous edits to this, sorry.

originally posted by: eManym
A vehicle moves forward in space because of a thrust expelled form on end. The vehicle moves in the opposing direction of the thrust. Why does the vehicle move at all if the particles expelled from the opposite end aren't reacting with anything? The vehicle and its thrust are a closed system. According to the law stated below, an external force must be present for the vehicle to move.

Newton's third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

What force is being exerted on the vehicle body to make it move?

The particles leaving to form the thrust are at constant velocity. They must have been accelerated to get that velocity.

a = F/m

Acceleration requires force and for every force there is an equal and opposite force. The opposite force is exerted by the vehicle and causes the vehicle to accelerate in the direction opposite to the accelerated fuel particles.

I will make a hypothetical example. I am in a space suit floating around in space. I need to get in motion to get back to my spaceship. So under the premise of what you just said, I can accelerate my arms outward periodically to get in motion back to my ship. Since my arms and body are a closed system, this won't produce any motion.

originally posted by: eManym
I will make a hypothetical example. I am in a space suit floating around in space. I need to get in motion to get back to my spaceship. So under the premise of what you just said, I can accelerate my arms outward periodically to get in motion back to my ship. Since my arms and body are a closed system, this won't produce any motion.

If your arms came off and had a velocity in the opposite direction of the direction to the space ship, then you would get to the space ship after some time.

Maybe if you had something to throw, and threw it as hard as you could, you would get back to the space ship before your air ran out.

The physics problem in class was throwing a ball while standing on ice. The thrower would slide backwards.

originally posted by: eManym
A vehicle moves forward in space because of a thrust expelled form on end. The vehicle moves in the opposing direction of the thrust. Why does the vehicle move at all if the particles expelled from the opposite end aren't reacting with anything?

Having been expelled and now separate from the vehicle, why would the propellant reacting with anything affect the vehicle?

The vehicle and its thrust are a closed system. According to the law stated below, an external force must be present for the vehicle to move.

If you want to draw the boundary of your system around both vehicle and thrust, you are right! The center of the vehicle/thrust combination does not move. However, as momentum must be conserved, the vehicle component of the system will move forward as the expelled propellant component moves backward, with the total system momentum change being zero.

What force is being exerted on the vehicle body to make it move?

The force exerted by the propellant being accelerated, if you want to look at it that way, which is the way I normally would.

originally posted by: eManym
I will try to answer my own question. It must be the pressure difference between the two ends of the nozzle the thrust is coming from. High pressure on one side of the nozzle and low pressure on the otherside.

The pressure ratio is definitely a component of the thrust equation, but not the only one.