As Lawrence Krauss explains in the above video, our universe is expanding uniformly in all directions, and we can tell this by studying distant galaxies.
This diagram illustrates how galaxies recede from each other due to As galaxies move away from us, the light (which is a wave) coming from the galaxies gets stretched out due to the Doppler-Shift. This stretching causes a shift of the wavelength towards the red end of the spectrum.
This is the visible spectrum (which is what the human eye is capable of detecting).Galaxies that are more and more red shifted, are further and further away from us.
This red-shifted galaxy, called A1689-zD1, is from when the universe was about700 million years old, not long after the formation of the first galaxies.
To better understand light and red-shift, imagine that a source of a light wave (such as a sun) is moving away from you (see image below).
Between emitting one wavefront and the next, the object emitting the light will have moved a little distance (Notice the dimmed representations of the sun above), and the second wavefront will have slightly further to travel. That means that the wave (or, the light) reaches you later than it would have done otherwise. (If, instead, the sun were moving toward you, the opposite would happen: The wavefronts would "smash" together, creating a shorter wavelength (the blue wavelength in the image above).So, we know that our universe is expanding. The current rate of expansion is usually expressed as the Hubble Constant (in units of kilometers per second per Megaparsec, or just per second).
Empty space is not empty!
Check out the animation at about 20 minutes and 50 seconds into the lecture. Most of the mass of a proton comes from the empty space between the quarks of a proton. The fields popping in and out of existence produce about 90% of the mass of a proton. (Since protons and neutrons are the dominate stuff in your body, empty space is responsible for 90% of your mass.)
When we calculate the energy of nothing, we calculate that the energy of empty space is a gazillion times the energy of everything we see. We calculate that empty space should have an energy of 120 orders of magnitude more than the galaxies and stars and people and aliens and all the rest. The symmetries of nature, however, allow the energy of nothing to be 0. What's so beautiful about a universe with total energy 0? Only such a universe can begin from nothing. This is remarkable because the laws of physics allow a universe to begin from nothing. You don't need a deity. You have nothing- 0 total energy, and quantum fluctuations can produce a universe.
As Lawrence Krauss explains, "Nothing isn't nothing anymore in physics. Because of the laws of quantum mechanics and special relativity, on extremely small scales, nothing is really a boiling, bubbling brew of virtual particles that are popping in and out of existence in a time scale so short you can't see them."
A growing number of scientific observations support the idea that dark energy is causing the universe to expand faster as it ages. The geometry of the universe adds more evidence to the case for dark energy.
General relativity tells us that space is curved (Space curves in the presence of matter.), and that because of this, the universe can be one of three different geometries: open, closed, or flat.
Weighing the universe tells us what the curvature of the universe is. Our universe is flat. It is flat because all the matter and energy that make up the universe creates a kind of universal balance. In other words, the geometry of the universe depends on how much total matter and energy it contains. If there is a lot of matter and energy, then the universe is curved at an angle that scientists describe as "closed." In that case, the universe would eventually collapse in on itself. With relatively little matter and energy, though, the curve is the other way, so it is "open" — it would expand forever, although at an ever-slower rate.
Our universe is expanding, but instead of expanding more slowly as it ages, it is expanding faster as it ages. The universe is flat, which means it must contain a lot of dark energy.
If you have nothing in quantum mechanics, you'll always get something. There is only 30% of the stuff in the universe needed to make it flat. Where is that other 70%? If you put energy in empty space, so that empty space weighed something, it would produce a cosmological constant, which causes the expansion of the universe to speed up over time. The amount of energy needed in empty space to make it speed up by the amount we measure it is exactly the amount we are missing (70%). Our new cosmological picture of the universe it that we live in a universe dominated by nothing.Clusters of galaxies are the biggest bound objects in the universe so if we could weigh them we could weigh all the mass in the universe. We can do this with the theory of general relativity. (27:23 in video)
Gravitational LensGalaxy Cluster 0024+1654
W.N. Colley (Princeton University), E. Turner (Princeton University)
J.A. Tyson (AT&T Bell Labs) and NASA
The weird blue things in the above image are a phenomena that we now understand as gravitational lensing. Einstein told us that a mass will curve space around it. Einstein realized, therefor, that if you had a big enough mass, and you have a source of light behind that mass, the light can bend around that object and come back, and be magnified. Mass can act like a lense and magnify things and split images, and that is precisely what we are seeing (the weird blue things). All of these blue things are different images of a single galaxy located about 3 billion light years behind this cluster. Gravity is magnifying, distorting, and bending this image. Because we understand general relativity we can work backwards and figure out how much mass must be in that system and where it is in order to produce that image. We can weigh the system using general relativity.
The image at 28:28 in the video shows the results of weighing the system. The spikes are where the galaxies are. Most of the mass in this whole system of clusters of galaxies is not where the galaxies are. It's between the galaxies. About 5o times as much mass in this system and in all systems we can measure comes from stuff that doesn't shine. Physicists call this stuff dark matter. We now understand that 90% of the mass of galaxies and clusters, including our own milky way galaxy is made of stuff that doesn't shine. We know how many protons and neutrons there are in the universe. We can actually measure that. There aren't enough protons and neutrons in our universe to make up all this dark matter. This is why we are pretty convinced that dark matter is a new type of elementary particle. Taking normal matter + dark matter and weighing it, we now have determined how much stuff there is in the universe. Omega is the ratio of the total amount of stuff we know is in the universe, divided by the amount of stuff you need to make a flat universe. The universe has only 1/3 the amount of matter to make it flat. In a flat universe, the total energy in the universe is precisely 0. This is because gravity can have negative energy. So, the negative energy of gravity balances out the positive energy of matter.
The cosmic microwave background is the afterglow of the big bang. This is just one of the many reasons that we know the Big Bang actually happened. If we look far enough ( to the birth of the universe), we should see the big bang, but we can't. Why? Because between us and the big bang there is a wall. The radiation in the past was so hot, that that is could break apart atoms, creating a charged plasma that is opaque to radiation. We can't see past this time, simply because the universe is opaque.
The largest amount of energy in the universe (70% dark energy) resides in empty space. We don't have the slightest idea why it's there. We are more insignifigant than we ever imagined. If you get rid of everything we see, the universe is essentially the same. We constitute a 1% bit of pollution., in a universe that is 30% dark matter and 70% dark energy. This has changed our picture of the future.
Cosmic natural selection
String theory
There is more we don't understand about the universe than we do.
Tidbits:
• The universe is the way it is whether we like it or not.
• Velocity is proportional to distance.
• The universe is huge and old and rare things happen all the time, including life.
• The energy of nothing.
• Take empty space- get rid of all the particles, all the radiation- absolutely everything, so there's nothing there, and imagine that nothing weighs something
• The universe we live in is the worst of all possible universes to live in.
"Every atom in your body came from a star that exploded, and, the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics: you are all stardust. You couldn’t be here if stars hadn’t exploded, because the elements - the carbon, nitrogen, oxygen, iron- all the things that matter for evolution and for life weren’t created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way for them to get into your body is if those stars were kind enough to explode, so, forget Jesus. The stars died so that you could be here today."
- Lawrence Krauss
For more information:
"Nailing Down the Discovery" at hetdex.org
"Hubble Finds Evidence for Dark Energy in the Young Universe" at hubblesite.org
"Redshift: The Second Most Powerful Tool in Astronomy" by Olaf Davis
emedicine.medscape.com
Universe Review
