Astronomers is Each Galaxy

Astronomers in Each Galaxy

and the fourth dimension

There are astronomers in each galaxy, and the light they see is also trapped on the curved surface of the hyper-sphere. As the sphere expands, the astronomer in any galaxy will think all the other galaxies are running away from him, and there are no privileged reference frames. The view that the universe looks by and large the same no matter from where we happen to view it was first proposed, so far as we know, by Giordano Bruno.

Well, the father away the galaxy, the faster its recession. The galaxies are embedded in, attached to space. And the fabric of space is expanding.

Horloge de la Tour. To the famous question – Where in the present universe did the Big Bang occur? – the answer is clearly, everywhere (quotations from Megan Jorgensen). Image © Elena

If there is insufficient matter to prevent the universe from expanding forever, it must have an open shape, curved like the saddle with a surface extending to infinity in our three-dimensional analogy. If there is enough matter, then it has a closed shape, curved like a sphere in our three-dimensional analogy. If the universe is closed, light is trapped within it.

Anyway, in such interdimensional contemplations, we need not be restricted to two dimensions. We can imagine a world of one dimension, were everyone is a line segment, or even the magical world of zero-dimensional beasts, the points. But perhaps more interesting is the question of higher dimensions…

Center of the Cosmos

Center of the Cosmos

Where is the center of the Cosmos? Is there an edge to the Universe? What lies beyond that? In a two-dimensional universe, curved through a third dimension, there is no center – at least not on the surface of the sphere.

The center of such a universe is not in that universe; it lies, inaccessible, in the third dimension, inside the sphere. While there is only so much area on the surface of the sphere, there is no edge to this universe. The universe is finite but unbounded. The question of what lies beyond is meaningless. Flat creatures cannot, on their own, escape their two dimensions.

Increase all dimensions by one, and you have the situation that may apply to us: the universe as a four-dimensional hyper-sphere with no center and no edge, and nothing beyond.

The center of the Cosmos is not in our universe (quotations from Megan Jorgensen). Image: © M. Jorgensen (Elena)

Why do all the galaxies seem to be running away from us? The hyper-sphere is expanding from a point, like a four-dimensional balloon, being inflated, creating in every instant more space in the universe.

Sometime after the expansion begins, galaxies condense and are carried outward on the surface of the hyper-sphere.

Orion Nebula

Orion Nebula

We can ask the computer to run a constellation forward into time. Consider Leo the Lion. The zodiac is a band of twelve constellations seemingly wrapped around the sky in the apparent annual path of the Sun through the heavens.

The root of the word Zodiac is that for zoo, because the zodiacal constellations, like Leo, are mainly fancied to be animals. A million years from now, Leo will look still les like a lion than it does today. Perhaps our remote descendants will call it the constellation of the radio telescope – although I suspect a million years from now the radio telescope will have become more obsolete than the stone spear is now.

The stars flash on and wink off like fireflies in the night (quotations from Megan Jorgensen). Image © Meg Jorgensen (Elena)

The nonzodiacal constellation of Orion, the hunter, is outlined by four bright stars and bisected by a diagonal line of three stars, which represent the belt of the hunter. Three dimmer stars hanging from the belt are, according to the conventional astronomical projective test, Orion’s sword. The middle star in the sword is not actually a star but a great cloud of gas called the Orion Nebula, in which stars are being born.

Many of the stars in Orion are hot and young, evolving rapidly and ending their lives in colossal cosmic explosions called supernovae. They are born and die in periods of tens of millions of years. If, on our computer, we were to run Orion rapidly into the far future, we would see a startling effect, the births and spectacular deaths of many of its stars, flashing on and winking off like fireflies in the night.

Appearance of the Constellations

Appearance of the Constellations

The appearance of the Constellations changes not only in space but also in time; not only if we alter our position but also if we merely wait sufficiently long. Sometimes stars move together in a group of cluster; other times a single star may move very rapidly with respect to its fellows. Eventually such stars leave an old constellation and enter a new one.

Occasionally, one member of a double-star system explodes, breaking the gravitational shackles that bound its companion, which then leaps into space at its former orbital velocity, a slingshot in the sky.

In addition, stars are born, stars evolve, and stars die. If we wait long enough, new stars will appear and old stars vanish. The patterns in the sky slowly melt and alter.

Time is important. (quotations from Megan Jorgensen). Image : © Megan Jorgensen (Elena)

Even over the lifetime of the human species – a few million years – constellations have been changing. Consider the present configuration of the Big Dipper, or Great Bear. Our computer can carry us in time as well as in space. As we run the Big Dipper backwords into the past, allowing for the motion of its stars, we find quite a different appearance a million years ago. The Big Dipper then looked quite a bit like a spear. If a time machine dropped you precipitously in some unknown age in the distant past, you could in principle determine the epoch by the configuration of the stars : if the Big Dipper is a spear, this must be the Middle Pleistcene…

Constellations

Constellations

Despite the efforts of ancient astronomers and astrologers to put pictures in the skies, a constellation is nothing more than an arbitrary grouping of stars, composed of intrinsically dim stars that seem to us bright because they are nearby, and intrinsically brighter stars that are somewhat more distant.

All places on Earth are, to high precision, the same distance from any star. This is why the star patterns in a given constellation do not change as we go from, say, Quebec, to Australia. Astronomically, Canada and Australia are the same place.

Dark Deep Space Reflective. Image in public domain

The stars in any constellation are all so far away that we cannot recognize them as a three-dimensional configuration as long as we are tied to Earth. The average distance between the stars is a few light-years, a light year being, as you remember, about ten trillion kilometres. For the patterns of the constellations to change, we must travel over distances comparable to those that separate the stars; we must venture across the light-years. Then some nearby stars will seem to move out of the constellation, others will enter it, and its configuration will alter dramatically.