Thanks,i knew you will b the first to comments.And many thanks you have given a huge source.Great!
In their excitement to convey the most recent thoughts on things physical, the writer loses only "style-points" - no doubt others will/have* carried the baton further down the road yet...
Thanks for the link. ed. 
* e.g. Roger Penrose, http://real.bnl.gov/ramgen/bnl/penrose.rm
(requires real-player) Had a brief look at the contents. For people like me, we need a patient study to understand what each theory really means.
nice | rshanthakumar wrote: |
| Had a brief look at the contents. For people like me, we need a patient study to understand what each theory really means. |
Yes, true enough. I had to study hard myself to get to where I am and I am by no means an expert in relativity. It *is* possible, however, and I would encourage you to take the time. It helps if you have some basic math - basic algebra is enough to get a good way and get a feel for the basics. To get deeper into the theory you really need calculus as well.
For anyone who wants to know how the universe really works then Newton is the starting point - look at Galilean/Newtonian physics and get a feel for simple momentum, acceleration and the rest. The next step is Special Relativity which is easier to grasp than the final stage -General Relativity.
I'll give you a quick summary of where this should take you with regard to special relativity.
In a nutshell, Newtonian/Galilean physics will show you that velocity is not a constant. This is easy to grasp - imagine a man on a boat. He regards himself as stationary even though the boat is moving. This leads to the conclusion that there is no 'absolute point' which you can measure velocity against - so we say velocity is relative, not absolute.
Newton regarded space as an absolute, however, in order to explain accelerated motion. His famous experiment was to spin a bucket full of water around quickly.
The bucket is suspended by a rope and then spun around.
Here's what Newton said about the experiment:
| Newton wrote: |
| the surface of the water will at first be flat, as before the bucket began to move; but after that, the bucket by gradually communicating its motion to the water, will make it begin to revolve, and recede little by little from the centre, and ascend up the sides of the bucket, forming itself into a concave figure (as I have experienced), and the swifter the motion becomes, the higher will the water rise, till at last, performing its revolutions in the same time with the vessel, it becomes relatively at rest in it. |
Here's a diagram showing the effect
Another way of imagining the problem is to use the example of your own body. If you spin on a spot, your arms will tend to rise. Now, if you were in deep space with no reference points, would this still happen? In other words, what would you be spinning relative to - there would be no reference points to tell you that you were spinning so would your arms rise? Newton decided that they would and that space, therefore, must be an absolute which we can measure movement against.
Later on, another scientist - Ernst Mach - spotted the flaw in Newton's reasoning. Imagine repeating the bucket experiment in a field. What is the reference point which the water is moving against and therefore changing shape on the surface? It could be your feet, or a tree, or a nearby landmark. But all of these are moving relative to space because the Earth is moving around it's axis and in orbit around the sun. Why does this motion not produce the same effect?
Mach thought that in empty space, with no reference points, the concept of spinning is meaningless, so there would be no difference between spinning and not spinning - leading to the conclusion that in such a case, your arms would not rise if you spun around. Or another example would be two weights connected by a rope. If you set them spinning then the rope becomes taught. Mach's argument was that this would not happen in completely empty space and the rope would remain slack. He thus denied that 'space' was a 'something' as Newton thought. A contemporary of Newton (Leibniz_ also thought that 'space' was nothing more than a way of describing where things are in relation to each other and had no independent existence in itself. Newton said otherwise and it was not until Einstein that the picture changed again (although there were other scientists who questioned whether space is a 'something' in itself - like Mach and Leibniz).
Einstein's Special Relativity gave us the current view of space.
Space is NOT a 'something' with absolute existence as Newton thought (in the same way that velocity is not an absolute and is only meaningful when measured against another point). Newton was close, though. Special Relativity tells us that time AND space, are inextricably intertwined together to form something we call 'spacetime'. Spacetime IS an absolute - it is a 'something, not just a lack of anything else.
It can be imagined as a loaf of bread and the relative motion of an observer can be imagined as a slice in the loaf. Different velocities are represented by a different angle of slice. Light slices the loaf at 45 degrees - this is the maximum angle possible. Here's a diagram I've lifted from Greene's book which illustrates the point:
The first picture shows one object slicing time as it moves and the second picture shown light moving relative to the object and slicing spacetime at 45%.
That, in brief, is where your study would lead if you decide to pursue this further. If you get to the point where you understand this notion of slicing spacetime at angles then I think you have grasped the important basics of Special Relativity...
References and Links
http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Newton_bucket.html
http://plato.stanford.edu/entries/newton-stm/
http://en.wikipedia.org/wiki/Newton%27s_bucket
http://www.iep.utm.edu/l/leib-met.htm
http://www.bun.kyoto-u.ac.jp/phisci/Newsletters/newslet_58.html
Whatever happened before the big bang was outside the bangs event horizon and as such could not have effected us. I think the more important question is "what happened in the first few seconds following the big bang."
Personally, I believe in the Big Crunch so I like to think that prior to the big bang, all matter was closing in on a certain point. Before that the matter was all expanding as it is now. Thinking about stuff on such a cosmic scale makes me feel tiny so I usually avoid it. | dwinton wrote: |
Whatever happened before the big bang was outside the bangs event horizon and as such could not have effected us. I think the more important question is "what happened in the first few seconds following the big bang." |
No, I think you are incorrect here. The BB was not a black-hole type singularity according to most theory. Current BB models are derived from the Friedmann-Robertson-Walker (FRW) solutions to General Relativity. The model shows that the BB lies in the past of all world-lines in the universe wheras a black-hole singularity lies in the future of all world-lines. In that sense the BB was more akin to the theoretical 'White Hole'. FRW BB models, therefore, have a completely different type of event horizon to that of a black hole. The Schwarzschild limit does not apply to rapidly expanding matter and a white hole has an event horizon which is the reverse of a black hole event horizon. Nothing can pass into this horizon just as nothing can escape from a black hole horizon.
| Quote: |
Personally, I believe in the Big Crunch so I like to think that prior to the big bang, all matter was closing in on a certain point. Before that the matter was all expanding as it is now. Thinking about stuff on such a cosmic scale makes me feel tiny so I usually avoid it. |
This is the cyclic model of the universe which, interestingly enough, has recently been revived by a small group of physicists.*
* http://www.actionbioscience.org/newfrontiers/steinhardt.htmlI think it was the Big Slurp 
Oh man... It was newer any bigbang, how can an earth with water an living stuff be made with fire and stones and gasses??? It would newer come souls out of that!
| Boffel wrote: |
| Oh man... It was newer any bigbang, how can an earth with water an living stuff be made with fire and stones and gasses??? It would newer come souls out of that! |
Errr......hmmm......I don't even know where to begin with this....
Let's start with a couple of basics.
1) The thread is not concerned with souls and whether they exist - that is a topic best debated in philosophy and religion.
2) I presume by 'newer' you mean 'never', in which case, presumably, you have an alternative theory? (If it's an ID theory such as creationism then please don't bother to elaborate - again that is best discussed in philosophy and religion, not science).Well, what did happen before the big bang?
Few schoolchildren have failed to frustrate their parents with questions of this sort. It often starts with puzzlement over whether space "goes on forever," or where humans came from, or how the planet Earth formed. In the end, the line of questioning always seems to get back to the ultimate origin of things: the big bang. "But what caused that?"
Some people simply proclaim that God created the universe, but children always want to know who created God, and that line of questioning gets uncomfortably difficult.
One evasive tactic is to claim that the universe didn't have a beginning, that it has existed for all eternity. Unfortunately, there are many scientific reasons why this obvious idea is unsound. For starters, given an infinite amount of time, anything that can happen will already have happened, for if a physical process is likely to occur with a certain nonzero probability-however small-then given an infinite amount of time the process must occur, with probability one. By now, the universe should have reached some sort of final state in which all possible physical processes have run their course.That is rather like saying that nobody wrote the Bible: it was. just copied from earlier versions. Quite apart from all this, there is very good evidence that the universe did come into existence in a big bang, about fifteen billion years ago. The effects of that primeval explosion are clearly detectable today-in the fact that the universe is still expanding, and is filled with an afterglow of radiant heat. So We are still Facing The Matter that what Hepped Before Bigbang. Many theories came with their Own Philosophies But Only bigbang gain popularity..... so still i have a big question mark sticking on my mind... 
| secondeye wrote: |
Well, what did happen before the big bang?
Few schoolchildren have failed to frustrate their parents with questions of this sort. It often starts with puzzlement over whether space "goes on forever," or where humans came from, or how the planet Earth formed. In the end, the line of questioning always seems to get back to the ultimate origin of things: the big bang. "But what caused that?"
|
The standard scientific answer is that the question is meaningless.
Spacetime as we know is started at the big bang. That means that time did not exist before the big bang and that, therefore, the concept of 'before' has no meaning.
Chris.I have a few questions about dimensions. I assume that time must be finite (at least in one direction) or we couldn't say that it began with the big bang. But are the other dimensions theoretically infinite? What dimensions exist beyond the information wave moving at c that started when the universe was born?
| Gagnar The Unruly wrote: |
| I have a few questions about dimensions. I assume that time must be finite (at least in one direction) or we couldn't say that it began with the big bang. But are the other dimensions theoretically infinite? What dimensions exist beyond the information wave moving at c that started when the universe was born? |
All the spatial and temporal dimensions are theorised to begin at t=0 (BB). If you accept that spacetime is all there is (4 dimensions, 3 spatial, 1 temporal) then the whole thing begins at the BB. String theories and M-theory posit extra dimensions which would extend back beyond the BB, but as far as the normal 3 dimensions we know then they all start with the BB.But do they start off as infinitely large? Is there space and/or time beyond the advancing edge of the universe? After the big bang, was there space and time everywhere, or just inside the bubble of energy that the big bang created?
| Gagnar The Unruly wrote: |
| But do they start off as infinitely large? Is there space and/or time beyond the advancing edge of the universe? After the big bang, was there space and time everywhere, or just inside the bubble of energy that the big bang created? |
Just inside the 'bubble' would be the answer to that one.
The standard scientific answer is that the question is meaningless.
Spacetime as we know is started at the big bang. That means that time did not exist before the big bang and that, therefore, the concept of 'before' has no meaning.
Chris.[/quote]
So, the trickiness in these questions is that two people can ask the same question and mean different things.
Science is "systemized knowledge derived through experimentation, observation, and study" but it is not the entirety of knowledge, per se. So within scientific terms, these questions can only be answered based on what is observable (i.e. measurable). That is why the Universe (all matter and energy) in science is finite and why time is finite as well and why we talk about the concept "before the Big Bang" as being essentially insignificant. If it is not observable or measurable, it does not augment any knowledge based purely on scientific framework.
In contrast, philosophy expands on the knowledge of science to ask questions that are still legitimate. That we cannot measure or observe something does not exclude its existence. In fact, it is precisely because we cannot measure or observe it that we are forced to acknowledge that for all purposes that it does exist, even if its existence is the sole interaction of that thing with the known Universe. So when you ask "what came before the Big Bang?" the answer is "Something but I don't know what." | benjmd wrote: |
| In contrast, philosophy expands on the knowledge of science to ask questions that are still legitimate. That we cannot measure or observe something does not exclude its existence. In fact, it is precisely because we cannot measure or observe it that we are forced to acknowledge that for all purposes that it does exist, even if its existence is the sole interaction of that thing with the known Universe. So when you ask "what came before the Big Bang?" the answer is "Something but I don't know what." |
On the contrary. The answer is simply "i don't know", because there is no reason to assume anything came before, or whether our conceptions of cause and effect even have any meaning then. | Indi wrote: |
| benjmd wrote: | | In contrast, philosophy expands on the knowledge of science to ask questions that are still legitimate. That we cannot measure or observe something does not exclude its existence. In fact, it is precisely because we cannot measure or observe it that we are forced to acknowledge that for all purposes that it does exist, even if its existence is the sole interaction of that thing with the known Universe. So when you ask "what came before the Big Bang?" the answer is "Something but I don't know what." |
On the contrary. The answer is simply "i don't know", because there is no reason to assume anything came before, or whether our conceptions of cause and effect even have any meaning then. |
Precisely correct.
The statement 'something but I don't know what' makes an invalid assumption. It assumes the existence of something. Whilst I agree that the fact that we cannot measure something does not preclude it's existence, it is illogical (and therefore not philosophically correct) to extend that, as you do, to state that because we cannot measure something then we must acknowledge it's existence. I cannot measure the size and mass of faeries but it does not follow that I must acknowledge their existence.
