Instant, instantly, instantaneous, and immediately either mean the same thing or they don’t. The most common definition of instantly is immediately. An instant, instantaneously, and instantly are not always exactly the same. Where are you getting. The phrase “an instant”?
Again, from the rules, so that at least I have some RAW support.: "Many spells are instantaneous. The spell harms, heals, creates, or alters a creature or an object in a way that can’t be dispelled, because
its magic exists only for an instant."
It seems you are saying others are shooting down your interpretation as you go point by point trying to disapprove theirs.
No, I'm trying to have some people shed their pre-conceptions and force others to use their interpretation, which relies not on RAW but on their own personal principles.
I don’t understand how you can say teleport has a time gap, but a boom does not.
Because the spell says that the first thing that happens after the disappearance (not the teleport, the disappearance), is the boom, it's immediately after.
If you say a spell happens with no gap
The rules only say that spells with an "instantaneous" duration happen in an instant. The rules NEVER say that there is no gap, so I don't say so either.
, then it is clear that the boom happens after the teleport.
And again, by saying this, you are trying to force the fact that there is no gap between the disappearance and the appearance in a teleport, which is NOT what the rules say. The rules ONLY say that the teleportation takes "an instant".
If a spell does have a gap, then wouldn’t boom-to-damage too? In that case, if you say the boom damage happens before reappearance, you are selectively choosing timing the time gaps.
No, I'm applying the spell as written, which says that after the disappearance, what IMMEDIATELY happens is the boom. Not the reappearance.
The 5e rules don’t define the chemical composition of air or the speed of sound (they also don’t define the color purple or say that humans are born with kidneys).
It would seem reasonable to carry over things not mentioned in the rules from the real world to assist understanding the truly magical things in a fantasy world, but that doesn’t have to happen.
Good, then we are in agreement, real earth physics do NOT need to happen in the fantasy world of D&D. The rules do NOT mandate this.
The rules also don’t mention a gap in time for teleportation.
No, but they also don't mention that there is no gap. As explained above, it takes "an instant". So a Star Trek teleportation is according to the RAW, it lasts only an instant, but not zero time, which is something else entirely.
Note that I'm not saying that there has to be a gap, it could also be that the disappearance takes an instant and the appearance as well, on top of a gap of just an instant. Lots of possibilities, and the rules don't forbid or mandate any of them.
If you want to make your game have one, you can, but that doesn’t add one to RAW.
As the RAW say nothing on the subject, saying that there is no gap is actually adding something to the RAW.
Saying that the description mentions teleport and disappear in different places doesn’t prove that they are different things with a gap between them.
Something is happening in between (the boom), so there IS some sort of gap.
Thunderstep doesn’t mention a gap in time; it does mention a gap in distance. Bridging distance is the underlying definition of what teleport means.
In an instant, in D&D rules. Not in zero time.
The spell’s description mentions that. There are instances in other genres that teleportation might have a time gap, but there is nothing in the this spell’s description that mentions a possibility of that.
The possibility is open in ALL teleportation spells, since they ONLY say that it takes "an instant", not zero time. But the suspicion is higher with thunder step because something DOES happen, the boom.
Thunderstep’s description does mention “teleport” without defining it in the description, but there is already a spell called Teleport that does clue us in that the process happens “instantly,” a synonym for “immediately,”
Not exactly. First, immediately does not mean "zero time either". Second, "instantly" is not used, "instantaneous" is used with the definition of the rules, which means "in an instant". Not zero time.
the word used for the boom that happens after.
If the spell meant for the caster to be able to negate their own damage from the spell, it would have mentioned that. A spell does what it says it does.
If the spell was meant to damage the caster if he did not go far enough, it would have mentioned that. A spell does what it says it does. In this case, it cuts both ways, you see.
Aside from the debate, my guess is that the spell’s writer used the word “disappear” as a synonym for teleport.
That is your very personal interpretation. I prefer to think that the writers used a word to say EXACTLY what it says it means, just the disappearance.
They didn’t consider the caster not teleporting out of damage range so described the boom in relation to the disappearance location.
And then maybe they did ? Maybe the authors of the most successful TTRPG in history were more clever than you or I and anticipated this reading, while still leaving the spell open to interpretation? Do you have any proof of what you are saying ?
Otherwise, the spell stands as written, with the word disappearance just meaning "disappearance" because it makes perfect sense as well...