What is the evidence that proves our universe is expanding?

"...Hubble finds proof that the universe is expanding

1929

The two keys to Edwin Hubble's breakthrough discovery were forged by others in the 1910s.

The first key, the period-luminosity scale discovered by Henrietta Leavitt, allowed astronomers to calculate the distance to variable stars from Earth. Hubble had already used this knowledge in his 1924 discovery that the Andromeda nebula, containing a variable star, was more than 900,000 light years from Earth -- way beyond our own galaxy -- a surprise to everyone at the time. With this scale and other tools, Hubble had found and measured 23 other galaxies out to a distance of about 20 million light years.

The second key was the work of Vesto Slipher, who had investigated the spiral nebulae, before Hubble's Andromeda discovery. These bodies emit light which can be split into its component colors on a spectrum. Lines then appear in this spectrum in particular patterns depending on the elements in the light source. Yet if the light source is moving away, the lines are shifted into the red part of the spectrum. Analyzing the light from the nebulae, Slipher found that nearly all of them appeared to be moving away from Earth. Slipher knew that a shift toward red suggested the body was moving rapidly away from the observer. But he had no way to measure the distances to these reddish bodies.

Hubble's brilliant observation was that the red shift of galaxies was directly proportional to the distance of the galaxy from earth. That meant that things farther away from Earth were moving away faster. In other words, the universe must be expanding. He announced his finding in 1929. The ratio of distance to redshift was 170 kilometers/second per light year of distance, now called Hubble's constant. The numbers were not exactly right, and refinements in measuring techniques and technology have changed all of Hubble's early figures. But not the basic principle. He himself kept working on the problem and collecting data throughout his career.

Some view Hubble's discovery as the most important event in astronomy in the century. It made the most basic change in our view of the world since Copernicus 400 years ago. His results showing that the universe was expanding supported a theory that had been proposed by Georges LeMaitre in 1927. A universe expanding, much like the aftereffect of an explosion, must have once been "unexploded," a single mass in time and space. ..."

http://www.pbs.org/wgbh/aso/databank/entries/dp29h...

"...The metric expansion of space is the increase of distance between distant parts of the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space. In other words, the universe is not expanding "into" anything outside of itself, although a frequently used analogy is the expansion of the surface of an expanding rubber balloon. If this analogy is used, this surface should be seen as an intrinsic manifold.

Metric expansion is a key feature of Big Bang cosmology and is modeled mathematically with the FLRW metric. This model is valid in the present era only at relatively large scales (roughly the scale of galactic superclusters and above). At smaller scales matter has clumped together under the influence of gravitational attraction and these clumps do not individually expand, though they continue to recede from one another. The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past) and partly to the repulsive force of dark energy, which is of a hypothetical nature, but it may be the cosmological constant. Inertia dominated the expansion in the early universe, and according to the Lambda-CDM model (ΛCDM model) the cosmological constant will dominate in the future. In the present era they contribute in roughly equal proportions. ..."

http://en.wikipedia.org/wiki/Metric_expansion_of_s...

"...Expansion of the universe. One of the reasons the universe is believed to be expanding is because of the phenomenon known as 'red shift'. Light, or other electromagnetic radiation from an astronomical object may be stretched, (due to a number of reasons) making its wavelength longer. Because red light has a longer wavelength than blue light, the effect of this stretching on features in the optical spectrum is to move them towards the red end of the spectrum. If then the optical spectrum of a distant galaxy shows features that are shifted towards the red end of the spectrum (red shifted), it can be due to one or more of the following three reasons:..."

http://www.thekeyboard.org.uk/The%20Big%20Bang%20T...

http://en.wikipedia.org/wiki/Redshift

It's called the red shift.

This is the same principle behind the Doppler effect, if you listen at the side of a road to the car engine, you'll notice that as the car approaches you the sound waves get bunched up so the tone of the engine is higher, as the car passes you and gets further away the tone of the engine is lower as the sound waves are stretched out. The same is true of light waves as galaxies fly away from us the light from the galaxies are stretched out and become redder. The faster the galaxy is moving away the redder the light becomes.

Now the more distant the galaxies are the redder the shift. How do we explain this? Clearly the more distant galaxies are travelling away from us faster than the closer galaxies. The only phenomenon that explains this behaviour is the universe is expanding.

Take a balloon and put dots on the balloon, then blow up the balloon, you'll notice as you blow up the balloon the dots become further apart, as you continue to blow up the balloon you'll notice that the bigger the balloon gets the rate at which the dots move apart increases. Hope this helps you to visualise why the galaxies are for the most part flying away from each other.

I say for the most part because galaxies aren't on their own they form local clusters and within that local cluster some can be on a collision course as is the case between our galaxy and the Andromeda galaxy.

The effects of the big bang caused the universe to expand.

Yes. There has been for decades (about six to be precise). Astronomers have measured the distance between galaxies and have found that those distances have increased. In fact, with the use of the Hubble Telescope they have been able to get much more accurate measurements, so they set out to determine how long it would be before the universe began collapsing back in on itself. Surprise! They found out that the rate of expansion of the universe is increasing!

In 1963, Arno Penzias and Robert Wilson, 2 scientists in Holmdale, New Jersey, have been engaged on a satellite tv for pc designed to degree microwaves. whilst they examined the satellite tv for pc's antenna, they found mysterious microwaves coming the two from all guidelines. in the beginning, they theory something grew to become into incorrect with the antenna. yet after checking and rechecking, they found out that they had got here across something genuine. What they got here across grew to become into the radiation envisioned years earlier via Gamow, Herman, and Alpher. The radiation that Penzias and Wilson got here across, called the Cosmic Microwave history Radiation, confident maximum astronomers that the huge Bang theory grew to become into extraordinary. for locating the Cosmic Microwave history Radiation, Penzias and Wilson have been offered the 1978 Nobel Prize in Physics. After Penzias and Wilson discovered the Cosmic Microwave history Radiation, astrophysicists began to verify whether or no longer they might use its residences to verify what the universe grew to become into like previously. in accordance to important Bang theory, the radiation contained ideas on how rely grew to become into allotted over ten billion years in the past, whilst the universe grew to become into in simple terms 500,000 years old. at that element, stars and galaxies had no longer yet shaped. The Universe consisted of a warm soup of electrons and atomic nuclei. those debris constantly collided with the photons that made up the history radiation, which then had a temperature of over 3000 C. quickly after, the Universe better adequate, and for this reason the history radiation cooled adequate, so as that the electrons would desire to combine with the nuclei to type atoms. because of the fact atoms have been electrically independent, the photons of the history radiation no longer collided with them. whilst the 1st atoms shaped, the universe had ordinary adjustments in density, which grew into the density adjustments we see immediately - galaxies and clusters. those density adjustments would desire to have delivered approximately ordinary adjustments in the temperature of the history radiation, and those adjustments would desire to nonetheless be detectable immediately. Scientists found out that they had an thrilling possibility: via measuring the temperature adjustments of the Cosmic Microwave history Radiation over distinctive areas of the sky, they could have a right away measurement of the density adjustments in the early universe, over 10 billion years in the past.

All major galactic structures are receding from Earth.