# I have three siblings, but some would say four

I have three siblings, but some would say four.
They say we are all, from the sky to the floor.

My brothers formed a band, but I wasn't invited.
Without me, you and the reaper will soon be united.

Who or what am I?

You are

Water

I have three siblings, but some would say four.

There were 4 classic elements: water plus earth, air, and fire (3 siblings). Aristotle added a 5th element, aether (the 4th sibling)

They say we are all, from the sky to the floor.

Everything was composed of the elements

My brothers formed a band, but I wasn't invited.

Earth, Wind, and Fire

Without me, you and the reaper will soon be united.

Water is necessary for life

• Correct on all fronts; well done. Commented Apr 5, 2018 at 1:36
• The 5th element was actually called Leeloo. Commented Apr 7, 2018 at 9:28
• I have three siblings, but some would say four - Alternatively, this could be related to Wu Xing - five classic Elements in Chinese philosophy: Water, Wood, Fire, Earth and Metal. Commented Apr 13, 2018 at 9:59

You aren't

Water.

You are

Gravity

I have three siblings, but some would say four.

There are 4 known fundamental interactions (or forces) in the universe: the Strong, Weak, Electromagnetic and Gravitational interactions. So gravity has 3 "siblings".

But some physicists suspect a 5th fundamental interaction may exist, which if true would make it 4 "siblings".

They say we are all, from the sky to the floor.

Everything in the universe is comprised of these quantum fields/interactions (or whatever it turns out that gravity has, if not a quantum field)

My brothers formed a band, but I wasn't invited.

The other 3 forces are all well defined by a single theory (the "Standard Model") which describes in one theory and one set of equations, the quantum fields making up the Strong, Weak and Electromagnetic interactions.

But gravity is the outlier - it hasn't been described by that single model, may never be, and therefore is the only one of the 4 not to be part of the Standard Model. In fact, so far we don't actually know that a quantum field theory exists for gravity, nor do we have any clear evidence demonstrating it will eventually be found or that this would be how gravity works.

Hence physics is pretty much "Standard Model" (describes 3 interactions/forces) plus gravity (separate), right now.

Without me, you and the reaper will soon be united.

It's true. Take away gravity and none of us would live much longer than it took the sun to fall apart (or maybe explode given the pressure needed to hold it together???), the earth and other planets to cease orbiting, and every human on Earth to leave the planet's surface and atmosphere.

In fact it's worse than that. Without gravity we wouldn't have stars, galaxies, or planets, nor any of the elements that make up complex chemistry, and which were formed by stars (most elements from lithium to iron, including all carbon and oxygen), and supernovae (exploding massive stars that both formed and collapsed because of the effect of gravity). So we wouldn't have existed in the first place.

• Clever. Not the correct answer (as you knew when you started), but I like it. Commented Apr 5, 2018 at 12:54
• Mhm!) Seems the answer you had in mind might even be less correct? ;-) Glad to have surprised you with a genuine answer! Commented Apr 5, 2018 at 14:18
• @Stilez: Why do you say the other answer is less correct? Commented Apr 5, 2018 at 15:11
• The other answer seems much more correct to me. Especially the third hint. If you're actually referring to a band, it seems a lot more obscure than the other answer's, and almost any combination three or less words is the name of some obscure band so I think you could fit any answer into that hint the way you did. Why would you say it is less correct?
– Paul
Commented Apr 5, 2018 at 16:16
• Its tongue in cheek ;-) to find an answer like that which isn't the expected kind, amused me :) this one was an answer *** years before humans devised the expected answer and will be an answer in *** years time, and would be an answer for any other sentient life form in the known universe. I kinda smile at that :) (sorry for *** , trying to avoid spoilers) Commented Apr 5, 2018 at 16:27

You are:

Earth (the planet)

Explanation:

I have three siblings, but some would say four.

There are three other inner terrestrial planets in our Solar system: Mercury, Venus, Mars. However, the asteroid belt is considered sometimes a still-born 5th inner planet.

They say we are all, from the sky to the floor.

From the outer space to the, well, Earth.

My brothers formed a band, but I wasn't invited.

The asteroids, of course. But Earth has a different orbit.

Without me, you and the reaper will soon be united.

If the Earth is destroyed, we'll all die.

• Alternately, the 4th sibling could be Ceres Commented Apr 6, 2018 at 18:21

Wild guess:

Oxygen.

Things which possibly fit:

Three or four siblings would be other members of Group VI in the periodic table ("from the sky to the floor"). Though I don't know if anybody actually excludes Po from that group... And "without me, you and the reaper will soon be united" - obviously, without oxygen, you'll die quickly. I don't know about the "band" part.

Well, obviously the right answer is up there, but here is what I had guessed:

You are:

The troposphere (part of the atmosphere).

Explanation: I have three siblings, but some would say four.

Stratosphere, mesosphere, thermosphere, and exosphere - that doesn't really work, unless you say one of the layers is part of another.

They say we are all, from the sky to the floor.
As a non-native English speaker, I didn't understand this as "everything" (although the comma was a strong hint).

Atmosphere is all there is between space (sky) and the floor (excluded).

My brothers formed a band, but I wasn't invited.

Doesn't match (I thought the upper layers were part of "space", but I was wrong).

Without me, you and the reaper will soon be united.

No troposphere implies no atmosphere => no life.

• This was my thought as well, and I actually joined the site to post this same answer until I found yours. Have an upvote, friend. ^-^ Commented Apr 6, 2018 at 16:15