how the heck do scientists know that the universe is expanding?

Answer 1

From the red shift of light from distant galaxies. This is a Doppler shift of the same kind that police radar uses to measure the speed of your car. We can measure the speed of distant galaxies, and they are all moving away. A few nearby ones are not moving away, and a few are actually moving toward us. But distant galaxies are ALL moving away, and the more distant they are the faster they are moving away. This is exactly the kind of velocity distribution you would expect to see from anywhere inside an expanding cloud of galaxies.

Answer 2

Because almost every galaxy that can be seen in the sky is moving away from us, and the farther a galaxy is, the faster it is receding. That means everything is moving away from everything else. If everything is moving away from everything else, then the Universe must be expanding.

Now if you want to know how they know galaxies are moving away from us, that is a little more complicated.

On Earth, when a noisy object like a car horn or a train whistle is moving toward you, the pitch is higher than when it is moving away from you. This is known as the Doppler effect, and it not only applies to sound, but to light too. When an object is moving toward you, it is slightly bluer, and when moving away it is slightly redder. At normal speeds you'd experience on Earth, the effect is too slight to notice. But galaxies are moving away very, very fast, so the redshift can be seen and measured.

That's how we know galaxies are moving away from us, and how fast they're going.

Answer 3

Because outside of our own Local Group of Galaxies, all other galaxies with the exception of a few are all receding away from us everywhere astronomers can see them. The further away they are, the faster they are heading away from us. As they speed away from us, their light is shifted towards the red end of the spectrum due to the Doppler effect, the same reason why train whistles drop in pitch when the train speeds away from an observer. In fact, galaxies and quasars have been found speeding away from us at velocities above 90 percent of the speed of light! When quasars were first discovered, astronomers could not make sense of their spectra at first. It wasn't until they realized the spectra were consistent with ionized hydrogen and other gasses but the spectra were red-shifted in the extreme. Even nearby galaxies are moving away from us at very high speeds. Virgo Cluster galaxies such as M-104 are moving away from us at over 700 miles per second, and other members are speeding away from us at nearly twice that speed. Because all but a very few galaxies are all rushing away from us in every direction and thus show a red-shift that increases with distance from the Earth, scientists have determined the universe is expanding. As it expands, it stretches the wavelenths of electromagnetic radiation travelling from one point to another in space.

Answer 4

The same way you know that a siren is moving away from you even if you can't see the car it's on. As the siren approaches you, it sounds higher pitched because the wave crests of the sound pass you faster and so it has a higher frequency. As it moves away from you the wave stretches out a bit and the wave crests pass you slower so you hear a lower frequency. This is called a doppler shift.

Astronomers look at the light doppler shift of stars and galaxies. This is called a red shift. If they see a low pitch (red) they know the object is moving away from us (or us away from them) and if they see a high pitch (blue) they know we're getting closer to the object.

When astronomers look at the redshift of most galaxies they see that they are generally moving away from us. Not only that, but the farther these galaxies are from us, the faster they seem to move away. It appears as if the universe is stretching out.

Answer 5

It doesn't make sense to consider the universe in a state of accelerated expansion The universe is not infinite so this scenario just can't be.
There are other explanations for the Doppler red shift.
If a galaxy happened to be in a state of accelerated collapse it's light would also be red shifted to indicate the recession of it's surface..
To prove this theory one would have to observe a galaxy from the other side,which is not possible.
It's just that the accelerated expansion theory cannot be.

Answer 6

Something known as the Doppler effect makes things going towards us appear to have a blue-ish tint and things going away at high speeds turns things red. In viewing distaant galaxies most have a red hue showing that they are going away from us. The more red the faster its going, also known as the red-shift

Answer 7

There are stars way out in space and they keep getting more distant. They measure the time it takes the light to reach earth.

At the site below, scroll down til you get to Hubble's portrait. "The Discovery of the Expanding Universe".

Answer 8

because of the Newton's law "an object in motion will stay in motion unless acted upon by an outside force" and everything in the universe is moving so the universe is moving and expanding because if everything in the universe stopped moving then the gravitational pull that objects exert on each other would disappear

Answer 9

by looking at different galaxies and finding out that they are moving away from us.