Hi people. I am sure this is talked about before. It is that I please want to know exactly how it is measured that the universe is expanding. It would be much appreciated if you would post it in this thread, so all facts about how astronomers and scientists have come to the conclusion that the universe is expanding and how exactly they measured this are collected together here. Thank you so much for your help...Please Register or Log in to view the hidden image!
Hi Banshee, This is my first post so bear with me...Please Register or Log in to view the hidden image! An expanding universe was an idea that grew out of one Edwin Hubble's discoveries, back in the 20s or 30s. He was the first person to fully realize that the Andromeda Nebula was actually a collection of millions of stars and other celestial bodies, and comprised what is now known as a 'galaxy'. He also realized that we are in a galaxy, called the Milky Way, and that there are many galazies in the universe. We now know that there are BILLIONS of galaxies in the known universe, each consisting of Millions and millions of stars. As these vast galaxies were studied, Hubble discovered a discrepancy in the wavelengths of light coming from these distant objects (the galaxies). The wavelengths were 'stretched out' further than they should be. Visible light was seen stretched into the longer wavelengths of infra-red, which meant that the space between our galaxy and the observed galaxy was lengthening! Which led him to deduce that the galaxy in question was moving AWAY from us at a quick pace. The more galaxies observed, the more he found had this so-called 'red-shift' or doppler-shift. A number of bodies were found to actually shoe 'blue-shift', which meant they were zooming TOWARDS us here in the Milky Way. But the vast majority of galaxies in the universe exhibit a red-shift. This led scientists to envision an expansion of all matter in the universe, and actually in the framework of Einstein's General Theory of Relativity, this meant that SPACE ITSELF was expanding. Indeed, most scientists of tha day wouldn't accept this vision of the universe, INCLUDING Einstein and Hubble. Edwin Hubble went to his grave with serious doubts about his own observations. Another key point is that, the further away an object is, i.e. the lengthier the red-shift, the faster it is travelling away from us. Many people saw this as evidence that WE here in the Milky Way were the center of the universe, which seems like a logical deduction, but it is not so. We are inevitably part of the expanding universe, the fabric of space-time that we are a part of is expanding outward all the time. There may well be NO CENTER! But that gets into some complicated cosmology, a topic for future discourse. Another fact is that no galaxies, as far as I know, display NO shift at all, therefore all galaxies are moving one way or another. None are static, they almost all move out from us. This chain of observations led to the Big Bang theory, as it is called now, still the most popular theory available so far, but still debated to this day. I don't know what else to add to this right now, if I am in error someone please correct me! PEACE
I don't think people actually know how large the universe is, but they determine how fast the universe is expanding by the effect called redshift, which occurs when a galaxy or single star is moving away from us at a great speed. For more info, look it up on the internet. Please Register or Log in to view the hidden image!
Thanx for the info guys. No, I do not wish to look it up on the internet. It is posted with a purpose here. I want answers from the people who are posting here at sciforums. I easily can think of looking things up on the internet myself. It is not the purpose of me, having started this thread, though... Please Register or Log in to view the hidden image!
Here, I found this while searching the web at: http://www.astro.virginia.edu/~jh8h/glossary/redshift.htm A redshift is a shift in the frequency of a photon toward lower energy, or longer wavelength. The redshift is defined as the change in the wavelength of the light divided by the rest wavelength of the light, as z = (Observed wavelength - Rest wavelength)/(Rest wavelength) Note that postive values of z correspond to increased wavelengths (redshifts). Different types of redshifts have different causes. The Doppler Redshift results from the relative motion of the light emitting object and the observer. If the source of light is moving away from you then the wavelength of the light is stretched out, i.e., the light is shifted towards the red. These effects, individually called the blueshift, and the redshift are together known as doppler shifts. The shift in the wavelength is given by a simple formula (Observed wavelength - Rest wavelength)/(Rest wavelength) = (v/c) so long as the velocity v is much less than the speed of light. A relativistic doppler formula is required when velocity is comparable to the speed of light. The Cosmological Redshift is a redshift caused by the expansion of space. The wavelength of light increases as it traverses the expanding universe between its point of emission and its point of detection by the same amount that space has expanded during the crossing time. The Gravitational Redshift is a shift in the frequency of a photon to lower energy as it climbs out of a gravitational field.