Does first move advantage even exist?

White for sure has an advantage. However, current popular theoretical opinion is that said advantage is insufficient to win. And as far as I know the Sicilian is more of an equalizer than the Grunfeld, but I don't know much about the Grunfeld, so I could be wrong on that. e5 is probably fine as well if you play the Berlin or something.

If you want to stretch it that far there is no such thing as an "advantage" - every position either ends in a forced win, loss or draw. "Advantage" is meaningless unless we assume flawed players. Another point is that advantage for one person might be disadvantage for another - depending on their knowledge of the situation. 

The "advantage" is alla bout Black playing reactive while White playing proactive. There are pros and cons to both, and White has a infinitesimally slight advantage because he gets to play proactive at move 1.

Opening theory changes every year... perhaps every month... but you feel that THIS TIME, they've got it exactly right and today's paradigm will never be overturned?

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But is that a definite advantage?

Did you ever consider, since the Knight cannot gain a tempo, since pawns cannot move backwards, and since no other piece can move legally on move 1, that White could possibly be in zugzwang on move 1?

Everyone knows the following position is lost for White if he is to move, and winning for White if it is Black to move:

Could the following position be the same situation?

Of course chess is a draw. The real question is how much of it is drawn? Is it barely a draw? Like...Black has one line in the Berlin and the Slav that holds and everything else loses by force? Or Black has quite a lot of room to play different things and still draw? I suspect the latter because chess has so many drawing mechanisms, but we cannot rule out the former until chess is solved basically.

Most people are fairly confident the game draws but we're less certain of the size of the drawspace (that is, all solutions to the game that end in draws). That's a question I've been very interested in. I have a hypothesis that as an opening variation starts to approach the edge of the drawspace the early midgames begin to have more forced repetitions.

Check out "secrets of modern chess strategy" by John Watson

#1

"I was curious if white actually has any advantage."
++ Objecively no. Subjectively yes: white has a wider choice of moves that keep the draw than black.

"The second most popular opening move for white (1.d4) is said to be equalized by the grunfeld." ++ Yes at the Yekaterinburg Candidates' Tournament Grünfeld was played 5 times and all ended in draws.

"If that's true that leaves 1.e4 as the only move to fight for advantage."
++ Yes so it seems. 1 e4 was most played and yielded best results in the YeketarinBurg Candidates.

"I know that e5 and the sicilian are both amazing replies to e4 but do either of them equalize for black out of the opening?" In the World Championship Carlsen-Caruana both 1 e4 e5 and 1 e4 c5 lead to all draws. In the Yekaterinburg Candidates white scored better with the Ruy Lopez, while black scored as much wins as losses with the Sicilian.

I guess that it depends on playing style. In OTB chess, I have always scored around 6/10 with white and 4.5/10 with black. Looking at the 500+ games I have played since joining here, I have got exactly the same statistics. 

In an important game (eg. County Match), I am always disappointed to get the black pieces.