Ask Ethan: Why are maps of the cosmos oval-shaped? (Synopsis)

"The bedrock nature of space and time and the unification of cosmos and quantum are surely among science's great 'open frontiers.' These are parts of the intellectual map where we're still groping for the truth - where, in the fashion of ancient cartographers, we must still inscribe 'here be dragons.'" -Martin Rees

We know the Earth is an almost-perfect sphere, yet maps of it always stretch it down to a two-dimensional surface. Outer space, too, when we look at it, offers views that extend deep into the cosmos in all directions, also on a sphere. But if you want to make a map of the Universe, you must stretch it down to a two-dimensional surface, too.

Image credit: Axel Mellinger’s All-Sky Milky Way Panorama 1.0 (2000). Image credit: Axel Mellinger’s All-Sky Milky Way Panorama 1.0 (2000).

These maps are almost always shown as oval-shaped, but there's a good reason for this! You cannot show, simultaneously, a two-dimensional projection of a sphere that is simultaneously: connected, area-preserving, free of shape-distortion, and where latitude and longitudes appear perpendicular. You can pick three at most, and the projection most frequently chosen for space, the Mollweide projection, is very different from the Mercator projection chosen for Earth.

Image credit: ESA and the Planck Collaboration, of the CMB in a Cartesian frame, distorting the areas around the poles significantly. Image credit: ESA and the Planck Collaboration, of the CMB in a Cartesian frame, distorting the areas around the poles significantly.

Go get the full story -- and see some amazing possible visualizations -- on this week's Ask Ethan!

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Projections can really mess you sometimes. i.e. in Mercator projection (most widely used for earth).. Greenland as huge.. as big as Africa... when in reality it's only about the size of Egypt.

By Sinisa Lazarek (not verified) on 27 Feb 2016 #permalink

I can't figure out how to ask a question to have you answer, and I don't know where on the Internet to find the answer. So I was curious about the fourth dimension and the end of time. If the Big Bang is continuously pushing out space as we know it then time would continue to move, but what happens when that process stops and everything in the universe settles in the position it is going to stay in? Will that mean that beings who can travel through the fourth dimension like we travel through the third will be able to travel to the last moment in time? I'm just confused on the process and would appreciate someone explaining it to me.

By Jonathan Quinlan (not verified) on 28 Feb 2016 #permalink

It makes the USA look a LOT bigger than it really is, too.

It may be why it's liked so much...

"So I was curious about the fourth dimension and the end of time. "

One of your problems is demonstrated by the badly formed statement here. These are two different things. Likely you're mixing up " everyday time" as the "fourth dimension" and time as the fourth dimension of the spacetime metric.

This is indication you need some significant remedial work to get the basics down right, I would suggest a look on Wikipedia.

"If the Big Bang is continuously pushing out space as we know it "

It isn't. Space is just expanding. Getting bigger. The big bang is loooong past and is doing nothing today.

"but what happens when that process stops and everything in the universe settles in the position it is going to stay in"

BB has already stopped. And if the expansion that is going on stops, either this is in finite time and the universe will collapse, or it's in infinite time and it will just coast to an asymptotic zero speed and never actually get there.

However, currently it looks like we'll keep expanding and it won't stop.

"Will that mean that beings who can travel through the fourth dimension like we travel through the third will be able to travel to the last moment in time? "

No, because we ALL travel through the fourth dimension. It's called "existing". It isn't, however, a dimension like forward or north.

So your beings won't exist.

So like I said, go to Wikipedia, look up the subjects and use them to start off book reading elsewhere.