Where is everybody?

[mightymrbob]

How come whenever I'm here no one else is? It's half six in the evening in england, what time is it "over there"?

And could someone please tell my STUPID STUPID MATHS TEACHER that there is a fourth dimension? I'm relatively new to this stuff, and whenever I try and explain it to him he doesn't listen and tells me to shut up.

Tut tut tut... Some people!

There are 11 dimensions, right? 10 spatial and 1 "time", right?

[Keiji]

It's half six in the evening in england

Yay, another person in England.

There are 11 dimensions, right? 10 spatial and 1 "time", right?

No, there are theoretically infinite dimensions. Time is not a dimension.

[mightymrbob]

Okay... Let's just say, "I knew that". lol

Sooo, er, I've been to Torquay... Ahem...

*Urgently requesting something, anything, to talk about*

Oh, and WOOHOO!! I'm no longer a pointspace citizen.
Oi you, out of my way. Bah. I can't jump that high!

Edit by BobXP: Please do not double post.

[Keiji]

You've been to Torquay? Cool

btw as you may or may not know I am a mod around here :wink:

[mghtymoop]

those who follow string theory believe there are either 10 or 11 dimensions + time (there is no evidence to support this theory)
infinate dimensions is an adaptation of string theory so time is also outside of the dimensional classification (again no evidence)
standard timespace theory suggests there are four dimensions in which time is the fourth and is spatial (relativity and gravity waves support this)
an adaptation of this is the crystaline fluid theory in which there are five dimensions in which time is the fourth and is spatial and a fifth fluid dimension is the mulitverse in which multiple 4d universes flow interacting through crystalline forms (there is little evidence to support this apart from some gravity anomalies observed in large bodies believe to be caused by an interaction with something unseen and without a temporal factor)

[mightymrbob]

Sorry Bob...
Anyhoo, thanks "mghtymoop", that should confuse him even more. Which one do you think is true?

[mghtymoop]

i am a strong beleiver of the standard 4 dimensional timespace theorum though i can see some merit in the 5 dimensional version
i cannot stand string theory because of what it surmises to do without producing any evidence whatsoever and the amount of weight that so many people give an untestable theorum

[mightymrbob]

I see... Well. I'm inclined to reserve all judgement 'till I know some more about 4D, etc.

[PWrong]

Of course there's no direct evidence for string theory. The extra six dimensions are curled up as small as the planck length. The evidence is that the maths works out and makes good predictions. There isn't very much evidence for relativity either. That's why it's called theoretical physics.

Relativity doesn't explicitly state that time is the fourth dimension, it just works the same way in terms of the equations. I read a bit of one of Einstein's own papers on relativity. I didn't understand much, but the time dimension thing seems like just an analogy. It just means that time can be compressed and curved just like a dimension, and objects tend to take the shortest path possible through the confusing Riemann surface thing.

Just about anything that mentions extra dimensions is theoretical.

As for your maths teacher, there's not much point in just saying that the fourth dimension actually exists, he might just think you read too much science fiction. Quote some important people or show him an article if you want to prove that you're right.

Otherwise, if you just want to confuse him, tell him that the universe is any or all of the following (don't ask me to explain any of these):

10 or 11 dimensional
Inside out (a naive interpretation of an advanced idea in string theory), Wrapped around a 4D version of a medievil horn (I read this in New Scientist, it's more complicated than that, but it sounds funny).

If that doesn't work, tell him a few things about matter:
Everything is made of tiny rubber bands.
Most matter probably doesn't exist.
Matter includes anti-matter, several types of dark matter, and now "mirror matter", (I've only heard of this once, but it's nice to include it anyway)

Quantum physicists beat the speed of light last year, and the government is now sending them extra funding using the technology. (This isn't some conspiracy, there's no secret to it. Singapore is planning a city-wide quantum network by next year. So much for Einstein)

Black holes can allow matter to escape.

Matter can be in two places at once, in two states at once, or both existent and not existent at once.

Matter is probably random... maybe

Again, don't ask me to explain any of that. It's basically a parody of modern physics, and it's not meant to be taken seriously. If all that was true, I'd take it as a proof of the existence of God... a God who really hates physicists.

[mightymrbob]

OK...
He'll probably have a heart attack after hearing all that!
Cheers anyhoo!


---

(many minutes later)

Bob's here!

[jinydu]

There isn't very much evidence for relativity either. That's why it's called theoretical physics.

There is actually quite a lot of evidence for relativity (that's why scientists are confident enough to teach some of it in high school). But, first, I should clarify things by saying that there are two Theories of Relativity: Special Relativity (SR) and General Relativity (GR).

As far as I know, SR is very well established. In one experiment, two jets with initially synchronised clocks were flown around the world. The difference in the readings on the clocks at the end of the flights were precisely what SR predicted they would be, within a (narrow, because atomic clocks were used) margin of error. SR is also supported by muon experiments. Muons are short-lived sub-atomic particles produced in the upper atmosphere. They are observed to travel much farther (on average) than predicted by "classical mechanics". This can be explained by time dilation, a consequence of SR. It turns out that SR correctly predicts the observed (average) distance muons travel before decaying. Today, the predictions of SR are routinely verified in particle accelerators, where particles are accelerated to well over 99% the speed of light (according to the laboratory reference frame).

The evidence for GR is perhaps not as complete, but there's still plenty of evidence going for it. In 1919, it was observed that light rays bend very slightly when travelling near the sun, as predicted by GR. Pound and Rebka measured that the frequency of light decreases ever so slightly (by the amount that GR predicts) when escaping the Earth's gravitational field. The Principle of Equivalence (one of the fundamental postulates of GR) has been verified to one part in a trillion. GR also predicts the existence of black holes, the evidence for which is considered conclusive by almost all astronomers. And most famously of all, GR predicts that the universe is not necessarily in a steady-state, but may be contracting or expanding (in fact, the steady-state is unstable. Give or take away a single atom, and the whole universe will contract or expand), and of course, Hubble discovered in the 1920s that the Universe is expanding. More information can be found at einstein.stanford.edu

[mghtymoop]

PWrong, yet again i have to explain science to a high school student, maths does not count for evidence, you cannot accept or deny any hypothesis based around mathematical formula, you have to do objective direct testing, you can and people have done direct objective testing of relativity, jindyu has been kind enough to give you some examples, however string theory is an entirely academic theory, it's just like it was assumed that you could walk from Australia to China in the 19th century, all the information from maps suggested it was possible, you could say that mathematically given the information that they had at the time it was possible, it wasn't until someone sailed all the way around the edge that it was proven wrong, now there isn't any evidence against string theory yet but scientific method states that you must have significant evidence for a hypothesis that outweighs any evidence against it to accept it, we as of yet don't have that for string theory and i woudn't be surprised if in the near future someone circumnavigates it.

[PWrong]

But, first, I should clarify things by saying that there are two Theories of Relativity: Special Relativity (SR) and General Relativity (GR).

I gave a explanation of special relativity and the Lorentz contraction in the science forum. I explained it myself to make sure I understood it right, and apparently I grasped the concept pretty well. So if anyone else wants more information, you could look at that.

There may be evidence for relativity now, but when Einstein first suggested it, the only evidence was the consistancy of the theory. Similarly, the only evidence for string theory is its consistancy. It's the only theory that agrees with both types of relativity and quantum mechanics (which has a great deal of evidence).

By agreeing with relativity, I don't mean that it agrees that time is the fourth dimension. The equations themselves don't require an extra dimension. It's just an easier way to visualise the situation.

Mghtymoop, how can maths not count for evidence? It's far more exact than direct evidence. Of course direct evidence is required eventually, but first you need to complete hypothesis so it can be tested.

Also, what sciencific theory isn't academic? Surely it's a good thing.

[jinydu]

In fact, I do know of one experiment that contradicted string theory (as well as most modern theories candidates for a Theory of Everything):

http://www.nature.com/nsu/030324/030324-13.html

The article (as can be seen from the URL) was published in Nature magazine, a highly respected journal. Despite some searching on Google, I haven't been able to find out what the response has been to this experiment among theorists. Strangely enough, I can't even find references to the study in later science articles.

I think that what mghtymoop wants to say is that neither self-consistency nor consistency with well-established facts is enough to demonstrate a theory's correctness. For example, Newtonian Mechanics is mathematically self-consistent, but around the turn of the 20th century, experimental results were found which contradicted the theory. It might be possible to formulate multiple (and mutually opposing) mathematically consistent Theories of Everything that agree (empirically) with both Relativity and Quantum Mechanics. You claim that string theory is the only such theory at this time, but how do we know that, in the future, someone cannot formulate another theory that also fits this criteria?

I've read before that the "real" test of a scientific theory is its ability to correctly predict experimental results AFTER the theory is published. Thus, it would be good (and arguably necessary) science to doubt the correctness of the Theory of Relativity in say, 1917, before conclusive evidence for it was obtained. We accept the theory only after many independent experiments confirm its predictions.

Remember, there are many theories in the history of science that seemed plausible when they were first proposed, but were later falsified. For obvious reasons, they aren't taught very often.

[mghtymoop]

The article is interesting however i would be interested in looking at the papers in the references however i have not been able to locate them or even an abstract to them except for at uchicago which requires password access. I tend not to put much weight in public magazine articles as they often take the most interesting but least significant findings and proclaim them as fact. however the idea of plank theory being denied is very appealing, i have never liked the idea that size could be quantised into finite minima, i much prefer the idea that you can have infinately small values just as easily as you can have infinately large ones

[jinydu]

I think that one reason Planck length and time may seem unappealing to some people is that it invalidates the concept of limits. Hence, all physical laws derived from calculus would be only an approximation, and never exactly correct. Furthermore, the notion of instantaneous velocity would be lost, replaced by an image of particles "teleporting" nonzero distances in zero time (like in movie frames). I'm not sure what impact this would have on Zeno's Paradoxes.

If I understood correctly, the reason quantised space and time was introduced in the first place was to get rid of infinities. For example, at the moment of the Big Bang, the Universe would have zero volume, infinite density and infinite temperature. For one reason or another, the theories could not handle these infinities. In order to overcome this problem, it was postulated that there is no such thing as a point (with dimensions all equal to zero) in space or time. Hence, zero would just become "very small but finite" and infinity would become "very large but finite".

[mightymrbob]

On the subject of the Big Bang.

at the moment of the Big Bang

I read somewhere that the "Big Bang" (and don't get me wrong, I don't believe in God) was just one of several "Big Bangs" that are caused by bubble-shaped parallel universes colliding..? This would mean the conventional Big Bang theory gets turned on it's head and is, as I wrote above, just one of many "Big Bangs" that can occur at any time..?

I don't know, I just read it somewhere.

[jinydu]

Yes, that is one of the views favored by many string theorists. The actual term for these "bubble-shaped universes" is "branes", and they have more than 3 spatial dimensions.

One advantage of this idea is that it answers the quesetion: "What caused the Big Bang?". Some people find this answer more satisfying than "It was caused by a quantum field fluctuation." or "You can't ask what caused the Big Bang because time did not exist before the Big Bang." In fact, it is possible to remove the "origin" problem completely by postulating that the branes have always existed and that they will continue to exist forever.

Another advantage is that it explains why our Universe is "fine-tuned" for our existence without simply resorting to the anthropic principle. It has been found that if any of the constants in nature had taken a different value (gravitational constant, speed of light, Planck's constant, etc.), the Universe would be inhospital to life as we know it. One explanation for why the constants take the values that they do is: "If they didn't, we wouldn't be around to observe them. Since we are around to observe them, they must take those values." This view (quite unpopular among theorists) is known as the anthropic principle. The "brane worlds" idea is one way to offer a more satisfactory answer. Since our Universe is formed by the collision of higher-dimensional branes, the same type of collision can occur in different places and times, forming other universes. If enough universes are formed, we shouldn't be surprised to see one where the conditions are favorable to life. An analogy is that if a billion people buy lottery tickets, we shouldn't be surprised to see at least one person winning, even though the chances of winning are very small. However, there may be other possible explanations. Perhaps the range of values the constants can take is not as wide as we think.

The biggest disadvantage that I know of to the "brane worlds" idea is that it is untestable (always a severe flaw for any scientific theory). Since we cannot observe these parallel universes, how can we be sure that they exist? Some other theories get around this problem by allowing indirect experimental tests that ARE possible using technology available at the time. But as far as I know, almost all predictions for this idea are currently untestable.

[mightymrbob]

So are all universes branes? :?

[jinydu]

According to this theory, all universes are formed by the collision of branes.

But please remember, this theory is far from proven.

[mightymrbob]

Cool... SO if all universes are caused by branes colliding, does that mean that the "offspring", as it were, has 4 spatial dimensions? If so, then does that mean that our universe has 4 spatial dimensions?!? Also, are all these branes and universes contained in a multiverse? Sorry for all the questions, I'm just mega -curious...

[jinydu]

I don't know much more about the theory (sorry, I just graduated from high school at the end of last May). You could try searching for it online.

[mightymrbob]

Cool. Thankyouverymuch anyway!

[RQ]

First of all, at least in our universe, there can't be 0 time, otherwise there would be total randomness. I've mentioned this before. According to Einstein time depends on velocity, which is true and you can find that out on your own by seeing that if everything was still, there would be 0 time. Furthermore, if in a closed system, like our universe, there was 0 time for all particles, then you would have infinities if you would like, because there would be no way to observe these particles if they had no motion. It would be the same as if they weren't there. And if you say that they are, then you're forgetting that there's 0 time according to our initial theory. There's no such thing as 0 time, so don't waste your time posting frail arguments otherwise.

[jinydu]

I was thinking about Planck length/time as something similar to movie frames. A movie is made up of a very large (but finite) number of frames. As I understand, movies work by playing Frame 1 for say, 1/60th of a second, then Frame 2 for 1/60th of a second, and so on until the last frame is reached. The time needed to switch between frames is (in theory) negligible. Suppose we could play the movie in ultra-slow motion. We look at an identifiable particle in Frame 1 (say a small ball). We observe that it remains stationary for 1/60th of a second. Then, it instantaneously jumps to a new position in Frame 2. I was thinking that Planck length/time would be qualitatively similar to this, except that the time between the frames would be MUCH smaller (but still finite). After, I meant to say that the image of instantaneous jumps seems unappealing to some people.

One more point. In mentioning Einstein and how time depends on velocity, I assume you are talking about the Theory of Special Relativity (SR). According to SR, if you observe a clock that is stationary with respect to you, the clock will NOT appear to stop (If you don't believe me, look at the clock on your computer's screen). It is only when the clock is travelling at a very high speed with respect to you that you observe the clock running slowly. In fact, the clock appears to run most quickly when it is stationary with respect to you (because the time dilation factor has its minimum value, 1).

[RQ]

Time is not discrete as you suggest. Frames in reality are made up of atoms, with spinning electrons. Time is continuous, and it cant be described via movie frames, as many comments through out the net say.
This would have to mean that the very fundamental parts (strings perhaps) have to be moving.
With respect to what you say? With respect to the universe's position. That's why they make up our universe.
Now someone could easily say, "What about Newton's 1st law of motion?"
Well, objects at rest are objects made out of atoms.
If you still think that I'm just making stuff up with this motion thing, just remember the uncertainty principle, and you'll see that all particles have to have a speed greater than 0, otherwise both their position and velocity could be known with 100% accuracy.

[jinydu]

Time is not discrete as you suggest. Frames in reality are made up of atoms, with spinning electrons. Time is continuous, and it cant be described via movie frames, as many comments through out the net say.

I suppose this means that you do NOT think that the Planck time (if it exists) is the smallest unit of time. You are not alone in that opinion.

[RQ]

Whether I am alone or not, I don't think time can have a fundamental unit as matter does.
With that respect, space can't have a minimal length either, because if it did, the velocity or speed in that region would have to be 0, making time 0, and causing it not to exist. This is Zeno's paradox, since how could space be connected with these gaps.
Perhaps I'm wrong, which is not unlikely, but until someone convinces me otherwise, this is what my opinion is.