question about space?

Question

if space has no end, then how do we know that its expanding? what the hell?

Answer 1

Stretching reality:

The universe is about 13.7 billion years old. Light reaching us from the earliest known galaxies has been travelling, therefore, for more than 13 billion years. So one might assume that the radius of the universe is 13.7 billion light-years and that the whole shebang is double that, or 27.4 billion light-years wide.

But the universe has been expanding ever since the beginning of time, when theorists believe it all sprang forth from an infinitely dense point in a Big Bang.

"All the distance covered by the light in the early universe gets increased by the expansion of the universe," explains Neil Cornish, an astrophysicist at Montana State University. "Think of it like compound interest."

Need a visual? Imagine the universe just a million years after it was born, Cornish suggests. A batch of light travels for a year, covering one light-year. "At that time, the universe was about 1,000 times smaller than it is today," he said. "Thus, that one light-year has now stretched to become 1,000 light-years."

All the pieces add up to 78 billion-light-years. The light has not traveled that far, but "the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away," Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger.

"It can be thought of as a spherical diameter is the usual sense," Cornish added comfortingly.

(You might have heard the universe is almost surely flat, not spherical. The flatness refers to its geometry being "normal," like what is taught in school; two parallel lines can never cross.)

Answer 2

We know that space itself is expanding because the sky is black.

The speed of light in a vacuum is constant for all observers, as predicted by Maxwell's Equations. Einsteinian relativity shows how two inertial reference frames moving with respect to one another can find this counterintuitive result, which has been proven.

We know, from Edwin Hubble's surveys and the research performed since then, that either space is expanding or objects are moving away from us. Since nearly all objects appear to be moving away from us at large distances, then either we are at the centre of the Universe for some reason (which is a whopper of an assumption, given Newton and Einstein's assertion that there is no preferred place of physical observation) or space itself is expanding and no matter where you are located it will appear that everything is moving away from you, which is a much more likely scenario.

Furthermore, since space is expanding then the objects being carried apart by this expansion are effectively at rest with respect to spacetime, and thus are exempt from Einstein's prohibition on relative motion greater than the speed of light; the motion is only APPARENT motion.

The furthest reaches of the Universe, that is those over 14 billion light-years away, are being drawn away from Earth by the expansion of space at speeds greater than light. The light from these systems is Doppler-stretched into nonexistence. And that is why the night sky is black.

Answer 3

We know distant galaxies are moving away from us by measuring the Doppler shift toward the red of the spectrum of light from them. The idea that space itself is expanding, not a cloud of galaxies expanding into previously empty space, is theoretically calculated, but I don't know how.

Answer 4

Because we can measure the angular distance from here to various objects in space using trig. When you do that over a long period of time, you will not that the distances are increasing...Why? Because the objects in space are moving away from each other. The distances between them are expanding. Hey...they (the things in outer space) are all moving...

Nobody ever said "SPACE WAS EXPANDING." What they said was that "OBJECTS IN SPACE WERE MOVING AWAY FROM EACH OTHER." People just assume that means space is expanding also...like a bag or a balloon.

Answer 5

By measuring the speed and directions of objects that we can see. That shows that everything is moving away from a common point. If they were all moving TOWARDS a common point, then we'd know that the universe is contracting.

Answer 6

Captain Kirk said so.

Answer 7

It's not that "space" itself is expanding, but that matter within it is moving outward.

Answer 8

We dont know. Scientists said so. Nobody can tell whether it is true or false

Answer 9

It is a measurement in respect to us.