I recently posted an answer to the following question:

How do we know that heat is a differential form?

and there were a large number of comments on my answer. I wanted to add another comment just now to ask those who had been involved in the discussion whether they thought that the answer could be improved in a particular way (by correcting a possible mathematical error) but found that all comments are gone.

I'm a bit sad because I thought (certain parts of) the discussion in the comments was illuminating.

What is the likely reason that the comments were deleted?


Don't have long discussions in the comments, instead create a room in chat. I can give you a screenshot of the comments if you want.

To be fair, it looks like you did that. However, the comments were still there and were cleared by a moderator -- they still cause clutter and reduce the signal-to-noise ratio. If there is useful information in the comments, the best thing to do is to incorporate it into the post; comments aren't as permanent.

Here are the deleted comments, though.

Comment discussions can be deleted if they get long. We usually wait a couple of days for a discussion to settle before doing this, though there are cases when we ask an active thread to move to chat and clear it if it ignores the request. However, if you want to recover the deleted comments, I don't mind providing them in most cases.

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    $\begingroup$ That's reasonable, and I actually like that policy. In this particular case, is there a way I can ping a specific user (Christoph) with whom I was discussing an issue in that thread? $\endgroup$ Feb 5 '14 at 3:53
  • $\begingroup$ @joshphysics I believe (I could be wrong) that comment pings still work even if the comment is deleted. Otherwise, I can ping him for you into a chatroom you create, though I'm going to take a nap right now. $\endgroup$ Feb 5 '14 at 3:55
  • $\begingroup$ Okay thanks for the help. $\endgroup$ Feb 5 '14 at 3:55
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    $\begingroup$ I actually hate this rule. Often significant, relevant discussions happen in the comments, that raise issues with answers, but they will get modded away into a chat area that people rarely visit. $\endgroup$ Feb 6 '14 at 22:22
  • $\begingroup$ @JerrySchirmer It's cleaner that way. You can always leave a link to the chat area in the comments. And, for that matter, look at the bigger picture -- content that really could be included in the visible answer is ferreted away into the comments. $\endgroup$ Feb 6 '14 at 22:26
  • $\begingroup$ On the other hand, a long discussion in the comments is hard to pick through, and other comments get lost in the process. $\endgroup$ Feb 6 '14 at 22:27
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    $\begingroup$ @Manishearth: then is it perhaps possible to suggest a threading system to the mothership? Movement to chat is more often than not just the killing of a discussion. $\endgroup$ Feb 10 '14 at 19:22
  • $\begingroup$ @JerrySchirmer Been suggested already. Comments on SE have always been an afterthought; the platform is for questions and answers and not for discussions. Surprised you say that movement to chat kills the discussion; it doesn't prevent further comment discussion and chat is more realtime. If you can explain why movement to chat kills the discussion, you may be able to put up a discussion post on Meta Stack Exchange $\endgroup$ Feb 10 '14 at 19:59

A direct answer your question would be kind of tricky because the effective "algorithm" used to decide whether to delete all comments on a post involves a balance between the number of comments, the relevance of the content of the comments, when they were posted, and so on, and ultimately it comes down to each individual moderator's judgment.

Speaking for myself, I'm likely to delete all comments when

  • there are a large number of them (enough that the "add/show N more comments" message appears)
  • the comment discussion is inactive (nobody has commented for a day or two)
  • the information in the comments is not essential to the post; or the comments are all old, like on the order of weeks or more
  • my attention is drawn to the post by a flag on the post or a comment

But in general, you should act as though comments can be deleted at any time for any reason. In particular, any information in comments that is useful to readers of the parent post should be incorporated into that post or another answer. And any time you find yourself going back and forth with someone in the comments, you should move the discussion to chat.

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    $\begingroup$ If this is the attitude, then why not just disable comments? What is the point of them? $\endgroup$ Feb 6 '14 at 22:22
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    $\begingroup$ @Jerry I believe that's basically because it's useful to have a mechanism to suggest improvements to answers. You can find lots of posts on Meta Stack Exchange from several years ago about why comments were introduced in the first place. $\endgroup$
    – David Z
    Feb 10 '14 at 17:47

The same happened for another question yesterday: https://physics.stackexchange.com/questions/98505/

All the comments were deleted by @dmckee. I am aware that the exchange was bordering the absurd, But I was interested in trying to analyze the intellectual mismatch that caused it. I would very much like to have a copy, if it is at all possible.

I understand the deletion, but it would be nice to have advance warning.

Sometimes the interesting part can be the exchange itself, rather than whatever science may be in it. But I know this view runs contrary to local policy.

This is not only not right, it's not even wrong. – David H 2 days ago

Do you know the story of this big truck that was carrying a hole for the foundation of a new house? There was a bump on the road and the hole fell off the truck. When he noticed he had lost the hole, the driver backed up to fetch it and reload it. But he failed to be careful and was never heard of again. - - - - - - - - - - - - - - - - By the way, what is the question you want to ask? There is no question in your text. – babou 2 days ago

i was originally looking for logical answers to the question is space nothing. I do like your response not only not right its not even wrong though. The story of the dump truck is not logical by any stretch though. It makes since that the "void" that is between everything from the largest of things to the smallest of sub atomic particles is what is generally thought of when using the word "space". Hence everything is in nothing and that nothing is referenced as space. Infinite and immeasurable in its greatness. It is where everything that is...is. – pjameslamar 2 days ago

Your question appears to be entirely philosophically-based and thus doesn't belong on a physics Q&A site. Also, it doesn't make any sort of logical sense whatsoever to say, nothing is where everything that is exists. There is no relation without relata. – Kyle Kanos 2 days ago

I feel that the eternal nothingness debate is some kind of philosophical juggling of language. Wouldn't the mere action of talking about nothing make it something? I think that this type of questions are above human understanding and we must remain silent. – jinawee 2 days ago

Heart Sutra? Form is empty. Emptiness is form.Form itself is emptiness; emptiness itself is form. So too are feeling, cognition, formation, and consciousness...the new physics? ;-) – V. Moretti 2 days ago

There is, BTW, a site dedicated to Philosophy. – dmckee♦ 2 days ago

@Kyle categorize my question about physics any way you like but because it is about physics it is a physics question anyway you slice it. I am simply asking is space literally the void that is between all particles no matter how great or small. My children come home from school spewing information given to them as science that has no logical foundation. If the void is something then it is not space as i or any logical person sees it. Everything that exists, exists in this void we call space and this space is literally nothing. yes or no? – pjameslamar 2 days ago

@jinawee talking about nothing doesn't make it something, my wife does it relentlessly...:)The argument that nothing is something is definitely beyond my understanding but the argument that nothing is nothing is quite logical. Like saying time is nothing but we reference it without thought all our lives. Time does not exist any more than and inch or a foot or a yard or meter....they are simply measurements. – pjameslamar 2 days ago

@V.Moretti that makes no since. Emptiness is containing nothing and form is the shape and structure of something. Like the hole in the dump truck babou mentioned above. – pjameslamar 2 days ago

@david z i had to ask the question as i did because of the rules of the site. My question is...is the area void of matter that exists between all matter space? It is a simple physics question so far void of logical answers. My physics question seems to be being classified as philosophical when its not. What i am seeing in discussion so far is a refusal to answer a simple physics question about the area between matter. A question easily understood but avoided by everyone so far. Everyone else knows good and well what it is im asking but you claim its unclear? – pjameslamar 2 days ago

@ dmckee there should be one for logical answers about simple physics. – pjameslamar 2 days ago

is the area void of matter that exists between all matter space? Was it so difficult to ask it this way? The answer to your question is yes, althought space in some sense will never be void, see en.wikipedia.org/wiki/Vacuum_state. – jinawee 2 days ago

My children come home from school spewing information given to them as science that has no logical foundation Or perhaps it is the case that you don't understand the logic behind the information. If this troubles you, you can always ask the teacher for guidance (or you can ask the question on the relevant website). – Kyle Kanos 2 days ago

Maybe the point of my truck story is that emptyness (nothingness if you prefer) is not something that is. But never mind. Another answer to your question may be that very simple questions may be hardest to answer, or to make sense of, or to explain. Would you accept the idea that an event can occur from within what you thought of being nothing. But then, is it nothing if it can give birth to observable events? So it may be that not a single stretch of space may be considered nothing. Maybe that means that space cannot exists without whatever fills it, whatever its name. – babou 2 days ago

@jinawee thank you. It was difficult to ask because the sight will not let one ask a question it thinks has previously been asked. To your answer you answered the question yes but then muddied the water saying it will never be void. Space itself is the void and matter of any type while in space does not completely fill this vast void we call space. To say space itself is something or that space is matter would mean that space has atomic definition and two atoms can not be in the same place simultaneously. They can be adjacent to each other but not simultaneously occupy the same place. – pjameslamar yesterday

@kyle kanos thanks. The teacher finally just stated "that's what the book says" Logic too is a science that deals with the principles and criteria of validity of inference and demonstration. So don't be snotty with me for asking a physics question. You are not the question police. Answer it or don't. It is a simple logical question many ask and just as many build careers on answering. You seem to be building your career on policing the question instead of answering it. The other gentlemen have answered. Do you have one? – pjameslamar yesterday

My answer to your post was given in my first comment: this is a (bad) philosophic statement and there is no physics question here. – Kyle Kanos yesterday

@babou thank you.Yes an event can occur within nothing. The observable events occurring within nothing (space) is the matter in space reacting with each other. There has to be space between the matter or the matter is always touching something else. On a grand scale or a minuscule scale. Space is mechanically necessary for the formation of matter. There has to be space to form atoms and molecules or everything would be one big mass. Matter can not exist without the space around it, the areas void of matter of any kind. Space is not anything. No atoms can simultaneously occupy the same place. – pjameslamar yesterday

@kyle kanos again, you judged my question but never answered it. You apparently are not good at judging questions nor good at answering them. Several other gentlemen saw fit to answer the question even in its original form. You continue to argue my question is in the wrong place. I submit that if you can reason it is in the wrong place you too can then reason what i am asking. I then reason that the problem is that you just are not able to answer and thus want the question moved because you feel obliged to answer as long as it is here. Answer the question or not? – pjameslamar yesterday

What question is there to answer? I see seven sentences. – Kyle Kanos yesterday

@Kyle Kanos, come on Kyle. Everyone else found the question. Its at the top. Is everything in nothing? Then followed by a short statement as the site requires. Many have argued that space itself is actually something. I simply argue that is illogical, improbable and impossible. "Space" is the area, void of all matter, that all matter exists in. Regardless the size of the matter. Others here have disagreed. Some agree but muddy the water with a however or a but. You must see the question, regardless of its form. Answer it or don't. You have the last word. – pjameslamar yesterday

The question "Is everything in nothing?" makes no sense. Something being (existing) in what is defined as not anything literally is nonsense. You are trying to defy the law of non-contradiction, which is just absurd. – Kyle Kanos yesterday

@kyle you understood it enough to say it was not a physics question. Now you argue it is contradictory? Let me help you. Everything is all matter. Nothing is the area (space) in which matter exists. Matter is something right? There is space, void of matter between all matter or else everything touches something else. Without space (area void of matter)there could be no specific things because all atoms and molecules would touch something else. Is everything in nothing? if yes end of discussion. If no then what is everything in? Nothing is "space". – pjameslamar yesterday

If you read some physics instead of saying it's all wrong, you would learn that fields are more important than matter, that the concept of to touch is ill-defined, etc. Einstein's theory make GPS work, we can measure the vaccum... Unless you make an specific model where you can predict observed phenomena, your theory is useless. All the greatest developments in Science were done in this way. If you want, you can say that the Spaghetti moster created us, but this is not the place. – jinawee yesterday

You sidestepped my question. Would you accept the idea that an event can occur from within what you thought of being nothing. That is you consider a stretch of space where there is nothing (you asserted yourself such stretches exist). No matter or anything else enters it from outside it, and yet an event is taking place from within that void. Can you still consider that this stretch is nothing ? Can you consider that it was nothing before the event, yet gave birth to an event with no outside input? – babou yesterday

@jinawee because something is written doesn't make it so. Lots of folks worshiped Newton and i believe Einstein stated he was not entirely correct either. Doesn't make Einstein absolute nor does it make Newton useless either. I never mentioned the spaghetti monster you did. LOL You and everyone else may disagree with my thought and im not offended. You saying i am wrong does not make me wrong. I will say a lot of proffered physics does not pass the science of logic. That is like saying something is invisible because you can not see it. Answer my question or not. It is legitimate. – pjameslamar yesterday

@babou thanks again for humoring me. Its kind of you. Again, yes, i accept the idea an event can occur withing nothing. I am thinking of all area where there is zero matter is "space". I think you think i am thinking in terms of a jar with a lid where ideally nothing can enter and this is not correct. The tiny area between atomic particles is space. The infinite vastness in which galaxies exist is the space i refer to also. Atoms exist in this space, so do planets and this space can not be a fabric of any kind. Like an idea. We all have them yet they don't physically exist yet they are. – pjameslamar yesterday

I read the first two lines and I stopped. You disagree with Physics and you say your theory is correct. Thank goodness that this is not that is not the way science works, we would be in the Middle Ages. I can only answer you from the current view of Physics, if not, people could answer that reality doesn't exist and all is made of rainbows... I don't say you're wrong, just that to accept your theory you have to destroy our current laws of Physics (and they are the main contribution for human progress). So I won't answer you more. Hope that at least you let your kids enjoy Science! Good luck! – jinawee yesterday

@jinawee thanks for reading the first two lines. Im no Einstein and i love science and logic equally. Did Einstein agree with everything Newton put forth? – pjameslamar yesterday

  • $\begingroup$ BTW--I'd strike "bordering the" and I think you're nuts to care, but I guess that is your look out. That said, I have little patience for people who seems to feel entitled to use Physics SE as a platform for their philosophy. $\endgroup$ Feb 12 '14 at 3:13
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    $\begingroup$ Oh...I'm going to nuke the rest of that thread sooner or later. $\endgroup$ Feb 12 '14 at 3:15
  • $\begingroup$ @dmckee Thanks a lot for the copy. I do understand how you and others feel. Maybe I simply have more time. But understanding science and communicating science is not obvious. It is a bit beyond knowledge itself, and I often feel that SE contributors from science departments, PhD students or others, are not very scientific and sometimes very ignorant too. I am painfully aware of my own lacks in physics, but I am not a physicist. I also wonder about the adequacy and dangers of SE for scientific exchange. In particular there is too much upvoted BS that no one will erase. ... $\endgroup$
    – babou
    Feb 12 '14 at 11:07
  • $\begingroup$ @dmckee (continued) Vote without justification is incompatible with my scientific ethics, especially for downvote. This is related to this elite-layman communication problem. - - - - - - - - - - - - - - - - - - - - - - - - - - Regarding the future nuking of the thread, I was expecting that and I am taking copies. But I am also trying to move the discussion elsewhere since no one else is interested :-) I only regret to lose competent supervision. $\endgroup$
    – babou
    Feb 12 '14 at 11:08

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