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Cosmology
Cosmology is the area of physics that studies the universe in and of itself. Through the use of incredible and ingenious methods of experimentation, cosmologists attempt to discover how the universe began, how it is developing, and how or if it will end. Questions regarding the Big Bang, dark matter, dark energy, the cosmic background radiation, and the initial formation of the fundamental particles can be placed into this category.
776 Questions
Dark matter wasn't "discovered" by any one person or group. In fact it is still hypothetical and there is no solid proof for its existence. Various astronomers inferred the existence of dark matter from what they observed about galaxies and galaxy clusters. It is still very much a mystery and the subject of some serious research.
What is the current theory of the start of the universe?
The leading scientific theory regarding the start of the universe is a cosmological model called the "Big Bang", which asserts the universe started out compressed, very hot and dense, that visible matter in its current form was consequent to an outward explosion. Evidence to support the theory includes the currently observable expansion of the universe, and a residual background radiation apparent in all directions.
Why couldn't Einstein accept that the universe was expanding?
Its not that he couldn't, he eventually did and declared his "cosmological constant" the biggest mistake in his life.
The situation was when Einstein developed General Relativity the prevailing cosmological theory was the Steady State Theory, that the universe was static. However General Relativity predicted that the universe could NOT be static: it must be either expanding or contracting. To correct for this apparent "error" and conform to the prevailing theory, Einstein added an arbitrary fudge factor that he called the "cosmological constant" that could be tweaked as needed to keep the General Relativity predictions in accordance with the Steady State Theory.
When it was clearly shown that Hubble's data was right and the universe was expanding, he willingly deleted the "cosmological constant" from Relativity.
How was the big bang theory developed?
The scientific process just says we shouldn't be afraid of being wrong. We think, we observe, we think again, we model, we check our model to see if it fits what we observe, we conclude, then repeat.
The Big Bang theory is a great illustration of this process because it starts with a simple perspective that only fits a small set of obseration and shows our progression to a more complete perspective that fits more and more observation. I am not a historian and do not know the timeframes of the theories and will definitely skip many theories of the universe because there are way too many to type up in a few hundred words.
First it was the world is flat. Then people noticed you could see the mast from far away, but not the hull. So there must be some curvature. Okay, earth is round.
Observation says that the sun, moon, and local planets do not orbit in perfect circles so they must have elliptical orbits. Still, what is rotating about what?
Years of observation later, we start seeing Jupiter's moons change direction in a cycle kind of pattern, we realize perhaps not everything is rotating about earth. Still no conclusion about that, but even more observations later we see galaxies and we come to the conclusion that earth is rotating on an axis.
Eventually it becomes accepted that the sun is the center of our solar system, planets orbit elliptically, and we may just be a typical star in our own galaxy. There was an interesting argument against an infinite universe. It says if the universe is infinite, there should eventually be light coming from a star at every point in the sky. Thus, since we don't see that, since we have night, we must have a finite universe.
So time passes, more observation. Debates go back and forth, is the universe infinite, finite, expanding, collapsing, stationary, etc. Newton makes earth shattering work on mechanics, his model of mechanics and gravity fit observation the best. It takes years to figure out the implications of his work.
Then someone proves that the previous result of the paradox is wrong if the universe is expanding or collapsing.
Enter Einstein, he fixes any inconsistencies in observations with his general relativity model. Then there is a huge debate about a cosmological constant, or an 'ether'. Is empty space really empty or what? Hubble I think proves that space is expanding because all incoming light is linearly redshifted. Meaning the farther away something is, the more it has been red-shifted.
So, since the universe is expanding, it must have started from some smaller state. Enter Big Bang theory. The big positives of the big bang is it fits the observations:
1) Space is expanding
2) Even background radiation in space
3) probably some others I cannot recall
The story doesnt end there. There are debates on the structure of space, how could a big bang even start, why the background radiation varies slightly from section to section, etc. Theres also a problem fitting the macro with the micro. Quantum physics predicts the micro, special relativity predicts the macro, but theres no crossing of the two. That doesn't make for a very satisfying theory.
Still a lot of questions, but with better technology comes better observations. With better observations, we 'hopefully' get better theories (general relativity wasnt derived from observations, but is extremely accurate). That's just the way of the scientific process.
A true vacuum, which is difficult to create, is a space where there is nothing. AN ordinary vacuum flask has "almost" a vacuum between its mirrored glass surfaces, but no matter how long the vacuum pump is trying to remove air from inside the glass walls there will always be some left.
By Willyrhus
Does dark matter affect the brightness of galaxies?
By definiton, "dark" matter neither emits or absorbs light. Thus, it does not effect the brightness of galaxies.
Is there any evidence against the theory of quantum cosmology?
Quantum cosmology is a field attempting to study the effect of quantum mechanics on the formation of the universe, especially just after the Big Bang. Despite many attempts, such as the Wheeler-deWitt equation this area of interest has yet to be fruitful.
Quantum cosmology is a branch of quantum gravity.
The whole point of dark matter ... the thing that makes it "dark" ... is that it doesn't interact with normal matter except through the gravitational force (and, possibly, for some potential types of dark matter ... remember that nobody really knows what it actually is yet ... the weak force).
One type of dark matter that we know about for sure is neutrinos. Around 65 billion neutrinos per second pass through every square centimeter of your body perpendicular to the direction of the Sun. They have been since you were born ... since before you were born, in fact. Even at night, because they go straight through the Earth too and come up through the ground on the side facing away from the Sun. The kajillion that have already done so haven't killed you yet, it's not all that likely that the kajillion and first is going to kill you.
About the only reasonably possible way to die from dark matter would be if there were a lot of it concentrated in one smallish area, in which case you could be pulled apart by tidal forces if you were in a spaceship that went too close to it. This also isn't likely to happen.
What is a sentence with cosmology?
- Cosmology based on the findings of modern science.
- I prefer to avoid the daoism or chinese cosmologyusually associated with tai chi.
- Cosmology elements of the a-level physics syllabus.
- The recent abundance of results from such observations has made the subject of particle cosmology blossom.
- In ancient cosmology, the planetary spheres ascended from earth to heaven like the rungs of a ladder.
- Cosmology experiments.
Why do you call dark matter dark?
"Dark" in the phrase "dark matter" comes from the fact that it interacts with ordinary matter only very weakly (at most) except through the gravitational force (and, for certain possible types of "dark matter" since we're not really sure what it is exactly, through the weak force, but that's strictly limited in range).
Since it does not interact through the electromagnetic force, and photons (light) are the gauge particles for the electromagnetic force, "dark matter" seems like a pretty reasonable name.
Don't confuse "dark" with "black": in order to be black, something has to absorb photons. Dark matter neither absorbs nor emits photons. This also means you can't feel it, since the apparent solidity of matter is also a function of the electromagnetic force. It is literally invisible and intangible.
Why is the big bang theory is doubtful?
The Big Bang theory is just that, a theory. Hence, the Big Bang theory. It has not been proven any more than the creation theory has. We have no irrefutable proof that it ever happened. This is what makes the theory so exciting as an inspiration for other work. The quest is for evidence that supports or refutes the theory as we understand it; that is how science works. Sometimes refuting evidence is found when it was not being actively sought, causing crises in the scientific community. Technically speaking, creationism cannot be classed as a science theory. Scientific theories must, in principle, be able to be refuted by some experimental or observational means. This doesn't mean that all theories must be refuted. But there must be some methodology or framework that could in principle lead to a refutation, if the theory is in fact not true. Related to this is the fact that for adherents of creationism, creation is the one and only option; in principle, it is denied from the start that there could even possibly be a valid refutation of what is assumed to be true based on faith.
ADDITIONAL EDIT: I want to point out a flaw in this answer. The word theory has a very different meaning to scientists. Theory means in the scientific world: A model that is repeatably supported by evidence and fully explains all known phenomena. A theory is not just a series of lgoical guesses, this is a hypothesis, a theory is the pinnicle of scientific creadibility. The big bang theory is supported by multiple feilds of science and there is no expereimental data of any kind to suggest it is flawed. There is in fact a large amount in accordance with it. This does not mean it is infallible, theories are often revised in the light of new data. However, theory means it is very very well founded, creationism is not a theory under the scientific meaning of the word. It is a belief.
What type of dark matter are WIMPs supposed to be?
No one has any idea what Dark Matter is. WIMPs are just one of many proposed theories for what it is. Another is that it might just be ordinary matter in a "parallel universe" only a millimeter or so away from our universe, but in one of the invisible 7 dimensions of the 11 dimensional Spacetime required by String Theory.
The Big Bang is the best theory we have, it is supported by abundant evidence, and is the closest we can get to the Univere's origin. The cause of the Big Bang is only speculation and may never be fully known, but that does not mean the Big Bang itself didn't happen. Some people put God as the cause, but that's not the only explanation. Whenever someone says the Big Bang is "just a theory" they are proving that they are ignorant because they don't know the definition of a scientific theory. In science a theory is far from a guess, conjecture, or speculation; it is simply an explanation backed by sufficient evidence.
AnswerThe big bang does not provide a theory of cosmic origins. The big bang is just a theory. I am a Christian so you can jest all you want, but the big bang is pretty much as possible as my God creating it because EVERY THING FROM SPACE TIME TO ASTRONOMY TO THE END OF TIME came from NOTHING AT ALL and it is possible that the universe came out of something that did not exist. I know that part of the theory is that the universe came out of a molecular explosion, but where did the molecules come from? If they were not there, as for the cosmic origin scientists will tell you that they came from clouds called nursery clouds, cosmic nursery clouds actually, and that the cosmos came from those nursery clouds. I believe that God made the cosmos. The cosmic origin could not have come from the big bang because it is as plausible as God being real to scientists. AnswerGod is my theory of cosmic origin. I am a Christian believer in God and the truth of the Bible. I also have no difficulty consolidating my belief in God with an acceptance of scientific explanations for the origin of the cosmos. I agree with the Big Bang theory as well as the theory of evolution by natural selection for living organisms on Earth. But I believe it all had to begin somehow, with something, before there was anything. It began with the First Cause of all things, God.I also highly recommend the book entitled "The Language of God" written by Francis Collins, who oversaw the Human Genome Project for several years.
AnswerSearch for materials on the newly emerging Membrane Theory. There are aspects of the theory that are extremely interesting and that allow physicists [theoretically] to go through and past the Big Bang, to meaningfully speculate about conditions existing prior to the Big Bang, and to explore some possibilities about what caused the Big Bang. I think this model harmonizes reasonably well with some faith-based approaches.Big Bang was coined as a term of derision toward those who first advocated the theory that everything was, at some time in the distant past, all in one place. There could have been no actual bang, because there was no medium through which sound could propagate. The Big Bang theory is indeed a theory of cosmic origin. There is no requirement that every theory be a 'theory of everything', or that the theory itself contain the answer to every imaginable question that it might inspire. A theory should account for current observations, it should be possible to test or search for evidence that supports the theory or that refutesit. And the theory should, as the questioner demonstrates, lead to further questions.
Philosophers of science can argue powerfully that no theory can actually be proven; this makes scientific work all the more tantalizing. The strength of the best theories is not that they provide clear, detailed and complete answers that are beyond challenge. The crumbling of theories in the light of new knowledge is a wonderful thing, even if not for the persons who devoted their careers to the crumbling theories. "The strength of theories is that they turn Mysteries into Problems." This statement is a paraphrase from: How We Make Decisions; Read Montague, Plume, 2006.
If you zoomed out of the universe what would it look like?
If one defines the universe as all the mater and energy that there is, then there would be no way to get "past" it, but even in the hypothetical situation that you were somehow able to be outside the bounds of all matter and energy (aside from yourself and whatever vessel you were in), you would see nothing -- complete blackness, because the matter and energy that make up the universe that you are beyond would include light. Light travels at a finite speed -- incredibly fast, but a finite speed. When an astronomer describes a star 15,000 light years away, that means the light from that star is 15,000 years old or, in other words, it has taken the light from that star 15,000 years to reach you.
The universe, as we know it, was created (according to most theorists) in an event called the big bang about 13.7 billion years ago. Light began to emit at that point, so the visible universe would have a radius of 13.7 billion light-years (or a diameter of 27.4 billion light-years). At the extreme edge of this radius, if one could somehow instantaneously get there, one might see the 'flash' of the big bang explosion that created the universe. Beyond that radius, one would be too far away to see the light from the very birth of the universe and there would only be a complete black void in every direction. No light from stars, not even cosmic radiation, complete nothingness.
If you'd like an idea of how various things compare in size to the universe, you can check out the related link. It's a little misleading in some ways (for one thing, it presents "strings" and "preons" as if they actually existed... the jury is very definitely still out on that), but it's basically correct about relative sizes. Keep in mind that it's a logarithmic scale, not a linear one!
How are stars dust and gas related to dark matter?
Stars, gas, and dust are all categorized as visible matter, not "dark" matter, but, since dark matter does not interact electromagnetically, the behavior of ordinary matter is used to study dark matter through their gravitational effects. You might say that stars, gas, and dust are like the leaves blowing in an invisible wind; the force can be perceived by the effects on the leaves even if you can't see the wind directly.
Are the Big Bang and a supernova the same?
No. The Big Bang was the origination of the universe; a black hole is the death of a star.
Answer
The big bang was an explosive expansion of space-time from a singularity, marking the beginning of time and space. Supernovae are exploding giant stars that form (and explode) millions or billions of years after such things as Big Bangs. The Big Bang was not a true explosion, but an enormous expansion. Supernovae are hugely closer akin to explosions.
What is the opposite of dark matter?
The word "opposite" is ill-defined here.
Also, we really don't know what dark matter is, so it's kind of pointless to talk about its "opposite", whatever that is supposed to mean.
How many dots represent the number of parallel universes in the multiverse?
The concept of parallel universes in the multiverse is theoretical and not quantifiable in terms of a specific number of dots. The idea of parallel universes suggests an infinite or unknown number of alternate realities existing alongside our own universe.
What is the temperature of Cosmic Backround Radiation?
Roughly 3K, close to the temperature of liquid hydrogen. It was billions of K when it first escaped following the Big Bang roughly 13 billion years ago, but the universe expanded and cooledas well as Doppler red shifted it until it looks very cold now.
About 2.725 Kelvin.
What observation led to big bang theory?
It was observed that the light from all objects in space was redshifted, meaning all objects are moving away from us. Light from objects further away was further redshifted. This would only happen in an expanding universe.
What is a light year used primarily to express distances?
Quite often they use parsecs, rather than light-years. In any case, it's fairly easy to visualize (for example) that Alpha Centauri is at a distance of 4.3 light-years - that means that light takes 4.3 years to travel that distance. On the other hand, giving the distance in meters, or in kilometers, results in very large numbers, that are a bit hard to visualize.
What is most of the universe made of?
About 5% of our Universe consists of baryonic matter; ie, stuff we fully understand.
Our Universe also contains about four times more mass in some form we DON'T understand, and that's why we call it "dark matter."
And about 75% of the energy of the Universe consists of something that is causing the rate of expansion of our Universe to speed up. It can't be something with mass, because mass would cause the rate of expansion to slow down. So it has be some form of energy we just don't understand -- so, for now, we simply call it "dark energy."
These two entities have nothing whatsoever in common other than the first word in the description we humans have given to them.
Why is the Big Bang Theory still logical If energy cant be created or destroyed?
It is quite clear, from observations, that the Universe is expanding, and that it started from a very hot and very dense start, currently called the "Big Bang". It is not quite clear where the energy came from; there are several speculations about this, but there is not much evidence about what happened before the Big Bang - or whether there even was a "before".
How come the universe is made of matter and not antimatter?
That is not currently known. There is a slight assymetry between matter and antimatter, but so far, it seems that this assymetry is not enough to explain why there is only matter, and hardly any antimatter, in the Universe. Without such an assymetry, there wouldn't be either matter or antimatter in the Universe - just radiation. For more information about what is known, and what isn't, check the Wikipedia article on "Baryon asymmetry".
In what way does the Big Bang Theory conform with the law of conservation of energy?
The law of Conservation of Energy states that energy can't be created or destroyed, so the Big Bang theory would condradict that.
