What is actually the difference between scales. For example 24.75 vs 25.5? or 25.5 vs 26.5?

I always thought that the longer the scale, the heavier the sound. But im not sure anymore.

I see most, if not all Les Pauls are 24.75 and i hear some recordings that sound darn heavy to me. Both detuned and not. The only "scientific" i've heard about scale length is that the short one (24.75) doesnt have as much of the high overtones/natural harmonics than for example 25.5. Which turns into a more heavy/rumble sounding power chord for example.

But i dunno. Educate me.
no real difference. 25.5 your strings are bit tighter, i guess that can affect teh tone slightly.

honestly man, this is hte kind of **** that affects like .5% of the overall tone. amp, guitar, pickups, body wood, etc all play a much bigger role so in the end the sound differneces between scales dont play a role at all.

it more abotu feel. i prefer 25.5 like my jackson, cause i feel there is more room higher up on the neck.
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it mostly effects feel, the string tension for the same tuning will be different, and the longer the scale is the more space there is between frets.
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I've heard you need thicker strings on a long scale to maintain the same type of tension as a short scale with thinner strings. Like....baritone guitars use thickass strings in B-tuning, where my 25.5 Schecter have far thinner string in the same tuning.

so, whats the deal here?
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I've heard you need thicker strings on a long scale to maintain the same type of tension as a short scale with thinner strings.

You've got it backwards: you need thicker strings on a shorter scale to maintain the same tension as thinner strings on a longer scale. If you usually play with light strings (9s) on a long scale, going up a string gauge (10s) on the shorter scale will feel about the same.

Next time you go to the guitar shop, try it out yourself -- you'll be able to feel the difference.
For me it's all about room on the high frets, I have pretty big fingers and I can barely play on the highest notes on my Explorer (24.75" scale? Something around there) but I was playing a 26.5" Schecter at Guitar Center and it was so much more natural for me.
It's mostly a feel thing. It affects your tone some, but that's more a pickup placement thing. It also affects your sustain a small amount. Guitars with shorter scale lengths will have just a bit more sustain that guitars with longer ones.