Word-Usage – ‘The Show is on a Break’ Meaning

A "while" is a length of time that is not defined. Used without a modifier, it implies one or more of the following:

1. The exact amount of time is not important
2. The speaker can assume that listener is familiar with the moment in time being referenced.

In your example, both of these probably apply. The teacher's point was made without specifying "10 minutes ago" because you knew of the conversation she was referencing.

The use of "short" or "long" becomes necessary if a more specific, but still vague, length of time is required for clear communication. Let's continue with your teacher example.

Imagine that the conversation she was referencing had occurred not ten minutes before, but a week. When she says that you said something "a while ago," you might reply "I don't remember saying that." Then she might clarify, "Well, it was a long while ago."

In this example number 1 in my list above still applies. The teacher can remain vague about the exact amount of time because the specifics are not important. However, because you could not recall the moment she was describing, more context was needed.

For a final example, suppose your friend came up to you and said "I saw Brad Pitt at the grocery store!"

You would love to see Brad Pitt for yourself, so you want to know if he is likely to still be at the store. You ask, "When?"

If your friend answers "A while ago," you don't have any new information to help you. You would have to press them for more information.

If they answer "A long while ago," you might as well stay home and watch World War Z again, because there is no way Brad Pitt is still at the grocery store.

If they answer "A short while ago," then you can run out to your moped and zip over to the store. He might still be there!

One final qualifier: "a short while" and "a long while" aren't very common in American colloquial English. You'd be more likely to hear "a little while" and "a long time," respectively.

Addressing your specific questions:

'Can you imagine how dirty it gets over time?'

When people talk informally, they are often a little sloppy. The present tense would be the perfect choice to state a generalization or natural law such as:

'White gets dirty over time.'

This idea was close enough for the speaker. Someone who likes to be more precise might say, instead, "Can you imagine how dirty it would get over time [if we bought the white pillow]?" But you might not enjoy living with someone who uses English precisely all the time. Such people tend to be nitpicky.

'The grease from your fingers will burn into the bulb and then it breaks.'

Here, two ideas have been spliced together into one sentence.

First idea: "[If you touch the bulb with your fingers] the grease from your fingers will burn into the bulb."

Second idea: "When that happens, i.e. when you touch the bulb with your fingers, the bulb breaks."

This is another example of the simple present being used for a generalization or natural law. And again, in a situation of informal speech you caught the speaker being a little sloppy.

'I hope it goes away overnight.'

I don't know how the English grammar experts would view this (if you want to know, you could ask over at ELU SE), but I will share how I see this example. My other primary language is Spanish, which has a subjunctive. English has one too, but people don't think about it much. In Spanish you really can't get away without thinking about it. In Spanish, this would be

Espero que se quite para mañana. ("se quite" is conjugated in the subjunctive)

I see the English sentence the same way -- I see goes away as the present subjunctive, which happens to be conjugated the same as the simple present.

Your questions were good, and you've done some careful listening and recording of what you've heard.

I would be remiss if I didn't point out a small but important misuse of the simple present tense in your question:

You wrote: I moved from Germany to California and since I'm here I hear people use the simple present....

Expressions beginning with "since" are notoriously easy to get tripped up on.

Better: I moved from Germany to California and since I've been here I've heard people use the simple present....

Or: I'm from Germany. Here in California I hear people use the simple present....