As recently as several years ago, the estimate was that anywhere from 3/4 to more than 9/10 of the universe was so-called "dark matter." Since then, however, dark energy has come to take over the top spot. Apparently, despite being energy that creates space, thus driving planets, stars, and galaxies apart from each other, it also has mass of its own. Not surprising, I suppose, in that in our everyday world matter and energy are simply transformations of each other. And yet, it's not clear that dark matter is a transformation of dark energy.

Here's a graph I found:

Notice that we live in the 0.4% slice and the observable visible is only about 4% of all there is.

BTW, the history of this topic should make everyone cringe whenever someone refers to a prevailing theory as "settled science."

Tags: dark, energy, gravity, matter, observable, universe

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And that's just one universe. Are there more? That's far from settled, too.

That's the strength of science... to be able to communicate to each other what we can know for sure (in measurements and predictions), versus what we know we need to learn more about. I'm speaking to religionists here, not our choir. I challenge religionists to learn what science has learned about space, gravity, lightspeed and bent light, mass, momentum, black holes, quasars, nuclear fusion and fission (e.g. inside stars). I also challenge religionists to help us detect life or even intelligent life on other planets, because we may well be on the cusp of that, next. What does your ancient scripture predict about it, specifically? Does it mention that science will lead the way?

I hope I wasn't taking your topic off track, even if the topic seems pretty wide open, at this time in history. But I often wonder if "dark energy" is nothing more than a spinning universe, flinging its parts apart. Yeah, there's no middle and no circumference, so we can't explain it or detect it as spin with respect to a center or outside space. But what if the dimensional aspects of "center" and "outside" just haven't been defined properly in terms yet of the 4 dimensions we already know? The only question then would be how universal spin (and maybe dark matter) interact in >4 dimensional space, or multiverse.

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It seems to me that if the universe is spinning, it would be spinning on an axis and we'd know where that axis is. There would be a big difference between being at the axis and being at the perimeter.

True, a spinning universe doesn't fit a standard 3D (2D plane + time around a center) axis/perimeter model.

But the deeper we peer out from Earth in all directions, the more clearly we can map the "center" (for lack of a better 3D concept) of our origin. On the scale of the universe, how we measure and describe "center" and "periphery" are themselves counter-intuitive in the 3D way we naturally conceive of space. The "center" of our universe is all around us.

I'll say no more. I suck at advanced math, which automatically disqualifies me from conceiving a decent model of non-euclidian space.

Something I read that shocked me was a description of what will most likely happen when the Milky Way and Andromeda galaxy collide. They both have one hundred billion stars and yet the chances of any star crashing or merging or interacting in any way with another one is very remote. To put the 0.4% (stars etc.) in perspective we should look at the size of stars and how far apart they are on a scale that we can conceive.

If the sun was the size of a base ball and we placed it in New York City ... then the nearest single star (Bernard's Star) would be a baseball in Paris or about San Diego. This amount of (so called) empty space is for me one of the most awesome things to contemplate. It stupefies me. This is a lot of room for dark matter and dark energy ... whatever the hell it is. I wish I was smart enough to study physics and investigate it. What an amazing adventure it would be.

" I wish I was smart enough to study physics and investigate it"

I have some trouble accepting that you're NOT "smart enough". Leaving your considerable intelligence aside, your humility and your awe form an excellent platform.

So when galaxies rotate, their outermost stars are orbiting its center much faster than is expected. A halo (or donut?) of dark matter (in theory) somehow explains why.

That's not much to go on, but science will keep solving mysteries like this, eventually. I mention this for the readers out there content with their faith that "God did it, move along now, science is just theories, nothing to see here, white Jesus is coming back, 'Genesis or Leviticus?', God bless American heterosexuals" anti-explanation. But I digress.

Cosmology is not an experimental science. A lot must be done by inference ("If such and such is happening, there must be something causing it to happen." These are proven, as much as they can, through observations. For example, observations have confirmed that strong gravity (black hole) can distort the path of photons (light).

It's true that when galaxies collide, relatively few stars and planets will collide, but they won't just pass through each other without interaction. Here's a simulation of a collision between the Andromeda and Milky Way galaxies:

Bodacious video unseen! Thanks for sharing :)

Do you know what kind of time scale we are looking at here? Does it reach billions of years?

I just watched Neal deGrasse Tyson say it would happen in 7 billion years.

Oh yeah. Four billion years, though that's an estimate based on what we know now. Revisions in the power of dark energy might add some millions or billions of years, but it won't be next Thursday. The Earth and probably humankind will be long gone by the time that starts happening.

Woah. That is incredible!

Could someone educate my ignorant mind as to how it is possible for two galaxies to collide when the universe is forever moving outwards? 

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