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Physics confusion

 
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Physics is a wonderful thing. It seems to offer so many answers to many confusing questions in life, and is the base of just about every other science. I very nearly picked it as one of my A-levels at school, but was a bit daunted by the maths side of it and plumped for Computing instead. The upshot of this is that there are several things about the universe that I never ended up studying, and confuse me to this day.

Mostly when I try to look up the answers to these things on the net there are only very confusing technical explanations which I do not quite understand. With this proving to be a bit of a dead end, I've decided to look for the answers in the next best thing - an internet forum full of bright, intelligent, friendly people, bursting with helpful advice and in-depth knowledge of the world. Unfortunately I couldn't find such a forum so I came here

Anyway, can anyone out there help to de-confuse me on the following:

1) We all know about the speed of light, and that nothing can go faster than it, but unfortunately the idea of an upper limit to speed is slightly unintuitive. Lets assume that I've built two spaceships A and B, each capable of travelling at 0.6c. A and B are tied together and then shoot off, using A's engines, and reach 0.6c. What would happen then if B detached itself and accelerated to its max speed? Common sense says that B should reach 1.2c, but then that would break the law about going faster than light.

2) If I pick up a rock and then drop it, it falls to the ground. Obviously gravity has done this, as the rock and the earth have attracted each other, but where has the energy come from to move the rock downwards? If any movement or change of direction requires the application of energy, then for the rock to start moving towards the ground, surely some kind of energy needs to be applied to it. If this is true, where does this energy come from? If laws of conservation mean that energy cannot be created out of thin air, then what is reduced/changed in order to "power" this movement? If the energy isn't "free", then it must come from somewhere, in which case why doesn't it run out or get reduced? If it is free, then can we harness it to make "free energy" (this seems odd and unlikely)?

3) If movement requires energy, is any energy used up to keep electrons spinning around the nucleus, or is it a bit like an object in orbit around the earth not needing any energy to keep it going? Why are electrons in atoms not attracted towards the protons in the nucleus? If they are, where does the energy come from to stop them crashing into each other?

4) I've read somewhere that its possible to change the spin of an electron in one atom and the spin of an electron in a specific other atom changes to become the opposite spin instantly, despite there being a considerable distance between them. What's this all about then? If this is true, what's to stop us creating a communication advice that works over vast distances, therefore breaking the rule about not being able to transfer information faster than light?

5) The good ol' Heisenberg Uncertainty principle. If I remember this correctly, for a particular type of particle (electron?) its impossible to know both the location and the direction at the same time. Why is this so?

6) Why have so many physicists got dodgy facial hair?

Any comments on these questions (helpful or not ) will be much appreciated. Please excuse my miserably high level of ignorance. Thanks!
 
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Originally posted by Joe King:

1) We all know about the speed of light, and that nothing can go faster than it, but unfortunately the idea of an upper limit to speed is slightly unintuitive. Lets assume that I've built two spaceships A and B, each capable of travelling at 0.6c. A and B are tied together and then shoot off, using A's engines, and reach 0.6c. What would happen then if B detached itself and accelerated to its max speed? Common sense says that B should reach 1.2c, but then that would break the law about going faster than light.



Not really. B is still moving at 0.6c, and its just that it appears to be moving at 1.2c relative to A. To get the correct speed of B, you should take a fixed point P in space and check how far away P is. Key is, to measure 'speed' of a moving body you need to compare the changes in its position from a static point, not a moving point.


2) If I pick up a rock and then drop it, it falls to the ground. Obviously gravity has done this, as the rock and the earth have attracted each other, but where has the energy come from to move the rock downwards? If any movement or change of direction requires the application of energy, then for the rock to start moving towards the ground, surely some kind of energy needs to be applied to it. If this is true, where does this energy come from? If laws of conservation mean that energy cannot be created out of thin air, then what is reduced/changed in order to "power" this movement? If the energy isn't "free", then it must come from somewhere, in which case why doesn't it run out or get reduced? If it is free, then can we harness it to make "free energy" (this seems odd and unlikely)?



I remember reading something about the Potential Energy of the stone when its static and the moment its dropped it starts accelerating towards Earth, and Potential Energy converts to Kinetic energy, and its somehow connected to speed & mass of the object in question - can't think of that formula at the mo.

I could be wrong but we have some excellent physics brains here in JR, and I am looking forward to some excellent explanations.

Cheers!
 
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Originally posted by Joe King:

I've got a dusty, twelve-year-old Ph.D. diploma in Physical Chemistry. I'll give it a shot.


1) We all know about the speed of light, and that nothing can go faster than it, but unfortunately the idea of an upper limit to speed is slightly unintuitive.


Your idea of a classical "top speed" for the rocket is faulty. Airplanes and cars have top speeds because they have to overcome friction to go anywhere. In a vacuum, there's no friction (well, of course there's no such thing as absolutely no friction or a perfect vacuum, but let's pretend.) A rocket can keep accelerating faster and faster as long as it can keep applying a backkwards thrust -- at least, classically.

Anyway, the short answer to your question: in Newtonian physics, your reasoning is correct. In relativistic physics, the faster you're moving, the more energy it takes to accelerate further, and it takes infinite force to accelerate a non-zero mass to c.


2) If I pick up a rock and then drop it, it falls to the ground. Obviously gravity has done this, as the rock and the earth have attracted each other, but where has the energy come from to move the rock downwards?


You put it in when you picked up the rock. It's called "potential energy." If that sounds bogus, think about if instead of lifting against gravity, you were lifting against a coiled spring. Winding up a clock, then, is storing potential energy to be later converted into the motion of the clockworks. You can also think about a child on a swing: when they're at the top, they've got a lot of potential energy but no kinetic energy -- they're momentarily still. When they're at the bottom, they have lots of kinetic energy and no potential energy.


3) If movement requires energy, is any energy used up to keep electrons spinning around the nucleus, or is it a bit like an object in orbit around the earth not needing any energy to keep it going?


The theory that electrons should spiral into the nucleus of an atom was the major objection to the first proposals for a planetary model of the atom; it was called the "ultraviolet catastrophe" (the spiralling charged electron would emit radiation as it plunged to its death, which would be in the ultraviolet range.) This doesn't happen, though, because energy is quantized. This means that energy comes in little packets called quanta, and can't be broken up arbitarily. An electron in an "orbit" (they don't really orbit, but it's an OK way to think about it for now; see the "Heisenberg" question below) has exactly one indivisible quantum of energy of a certain frequency; this frequency is analagous to the frequency of an orbit.

An object in orbit around the Earth does, actually, need energy to keep it up. Without periodic course corrections, orbital energy is lost to gravitational drag, and the body will eventually spiral down and crash (remember SkyLab?)



4) If this is true, what's to stop us creating a communication advice that works over vast distances, therefore breaking the rule about not being able to transfer information faster than light?


It's not that you can arbitrarily change the spin of one and thus change the spin of the other; it's that a spin measurement on either end is random as long as you only measure one spin, but once you measure on one end, the spin on the other end is determinate.

This is called the EPR paradox or "quantum entanglement" or sometimes "spooky action at a distance", and physicists are still arguing over it. It's generally felt that it doesn't violate the speed-of-light thing because no information is transmitted: the two particles form one big "wave" and are connected, somehow.


5) The good ol' Heisenberg Uncertainty principle. If I remember this correctly, for a particular type of particle (electron?) its impossible to know both the location and the direction at the same time. Why is this so?


There are all sorts of ways to explain this. Here's one: remember we're talking about very small particles, and remember that energy comes in tiny little packets (quanta). If you hit a tiny particle with a quantum, it either "moves" (absorbs the quantum) or totally ignores the quantum. Finally, note that the only way you can detect or measure anything is to hit it with another particle or a quantum of energy.

So imagine trying to determine both the position and velocity of a tin can by throwing baseballs at it blindfolded. If you hit the can, you know exactly where it is (was, anyway!) but you have no idea what its velocity vector is. If, on the other hand, if you miss the can, you know its velocity is exactly zero, but you're not really sure where it is.


6) Why have so many physicists got dodgy facial hair?


One of the great unsolved problems in physics.

 
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Here's what i remember from my classes:

1) As things speed up, they become more massive. More mass = more energy to accelerate. when you reach the speed of light, you have infinite mass, so you can't go any faster. That is an absolute, as i recall.

BUT, time also slows down. So the two ships, relative to each other, will be separating at .6c. I'm not exactly sure what happens to me, standing on their launching pad. but since time slows down for ship B, what the pilot thinks is 1 second is to me 1 minute. so HE thinks he travels 111,600 MPS, I see it as 111,600 Miles per Minutes (or however the math works out.

Why does time slow down? it's fairly safe to assume that the speed of light is constant (within the same medium). It may have even been proven somewhere. imagine i have a flashlight that emits 1 photon of light (we're going to ignore the duality principle for this). I shine the light straight down, it hits a mirror, and comes back up to my detector. knowing how far the photon travelled and the time, i can calculate the speed (d/t) = speed. easy enough.

Now imagine i perform the same experiment in a car on a VERY FAST train. to me, the photon goes straight down, and straight up, travelling 2 meters. it takes [not a lot of] seconds.

But to an observer standing by the tracks, the photon takes a much longer path. it travels slantwise down and back up, for a much longer total distance. To him, the photon travels 1.5 meters along the hypotenuse down, and 1.5 meters back up. again, i can calculate the speed. But since the speed of light is constant, i now have (2/time in car) = (3/time on ground). these times better be different!!! In our case, what seems like 2 seconds to the person in the railroad car seems like 3 seconds to the person by the tracks.

2) The energy is already IN the rock. It's called Potential Energy (PE). It's stored, waiting to be released, just like gasoline has potential energy, released if you light it and provide Oxygen. There is something preventing the PE from being converted to Kinetic Energy (KE) - the ground or your hand. Remove that, and it falls.

3) no idea, but i'll ask my sister the chemist and brother in law the physicist.

4) see 3

5) I think it applies to many things. The ACT of measuring the location CHANGES the direction. Similarly, measuring the direction CHANGES the location. Say you want the temperature of water, so you insert a thermometer into it. Since the device and the water are not the same temp, some of the heat in one will flow into the other, CHANGING what we want to measure. Granted, it's pretty small - really negligible for most things. but it is there. Same with measuring an electron. your sensors will change the very thing you want to measure.]
[ August 04, 2004: Message edited by: fred rosenberger ]
 
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Let me take a stab at Heinsberg:

Speed is d/t. Thus, given two endpoints, and the elapsed time, we may determain the average speed between these two points. However, we can't give the exact speed at any given location, because the overall is just an average. Erhm... better way to express my thoughts: To take a speed measurement requires two points. Thus, you can never Identify the speed with only the one point. To know something's location, you need a freeze frane of it in only on location, which precludes any measurement of speed. Do I make any sense? I think i understnd it in my head, but I'm having a tough time pulling it out. Measuerment of speed REQUIRES elapesed distance and elapsed time, and measurement of location requires ONLY a single "frame."
 
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Joe King:

1) We all know about the speed of light, and that nothing can go faster than it, but unfortunately the idea of an upper limit to speed is slightly unintuitive. Lets assume that I've built two spaceships A and B, each capable of travelling at 0.6c. A and B are tied together and then shoot off, using A's engines, and reach 0.6c. What would happen then if B detached itself and accelerated to its max speed? Common sense says that B should reach 1.2c, but then that would break the law about going faster than light.

The answers by others above are all quite correct, but I'm going to try to give you a different way of looking at the same thing.

You are thinking of things as if there were a fixed, preferred coordinate system, or frame of reference, that everyone used. In other words, the hidden assumption in the way you worded your question is that everyone measures speed in the same way. You are assuming that if I think I'm standing still and you're walking away at 3 miles per hour, and we both see someone drive by in a car, we'll both agree on its speed - if I think it's moving 3 miles per hour faster than you, you'll think so too.

What relativity theory says is that that isn't true - that things like velocities are relative, that what speed something is going at is relative to who is doing the looking.

So, suppose you're in space, with nothing nearby, not accelerating, just floating. You're moving at zero velocity, right? Of course, time is passing for you, so you're actually moving through time, into your future, just not through space. In a four axis coordinate system, one for time and three for space, your velocity vector would have a nonzero time component - since you're going into the future - but zeros in the three spatial components, since you're not moving through space. With me so far?

Now suppose the two of us are both floating in empty space, moving away from each other at a constant 3 miles per hour, neither of us accelerating. To each of us, it looks like we're the one who is still and the other person is the one moving. So which of us is actually still, and which of just thinks he is still, but is actually moving at 3 miles per hour?

What relativity says is that each of us is actually right - in our own coordinate systems. In my coordinate system, I'm still and your moving away at 3 miles per hour, in your coordinate system, you're still and I'm moving away at 3 miles per hour. This is possible because the "future" direction in my coordinate system - the one I'm moving along - is different from the "future" direction in your coordinate system. You can think of it as there being a slight angle between my idea of "future" and your idea of "future"; the two "future" directions are at a slight angle from each other. If I could point into my "future", you would see that direction as "future and slightly away".

What about the spatial directions? Well, it turns out that they're at an angle to each other, too. If I point in a direction that is "away" from you - using my coordinate system - you'll see that direction as "away and slightly into the future".

What about light? Suppose a photon comes whizzing by us both, as we're drifting apart. What direction is it going in? Relativity says that light is constant. Your coordinate system and my coordinate system will both agree on the the direction that the photon is moving in - and as a result, we'll agree on its speed, too.

So far, so good. We agree on the photon, and with respect to each other, we agree on our relative speed, even if we disagree on who is doing the moving. Even if we're moving apart at 0.6c, we'll agree on these things. We'll disagree on which direction is "the future" and which direction is "away", but so far, that's just a theoretical disagreement.

Okay, now suppose I, moving away from you at 0.6c, launch a bullet away from you at 0.6c relative to me. How fast do you think the bullet is moving?

Well, from my point of view, I launched the bullet "away" from you - but remember that we don't agree on directions. From your point of view, I didn't launch the bullet "away" from you, I launched it "away and somewhat into the future" from you. So what does it mean for something to be moving at 0.6c on a path that's "away and somewhat into the future"?

Well, let's both watch the bullet as it travels towards its target. After one of my years, it's 0.6 light years away from me, using my definition of "away". From your point of view, though, it will be 0.6 light years "away and somewhat into the future" from me, whatever that means. So what happens if we add up the vectors?

Okay, I'm not going to do the exact arithmetic; instead, I'm going to use round numbers that illustrate the principles. So don't trust my exact numbers in the next couple paragraphs, just think of them as examples.

First off, let's take my own direction relative to you. Recall that my "future", including my velocity of 0.6c away from you, is "into the future and somewhat away" for you. So after a while, I'll be at one year "in the future and somewhat away" from you - about 1 year into your future and 0.6 light years away along your distance measure, since I'm moving away at 0.6c.

In addition, the bullet will have travelled 0.6 light years "away and somewhat into the future" from me, using your coordinate system, since that's the direction you saw me fire it in - perhaps about 0.6 light years away and 0.3 years into the future from me. Total it up, and you'll see that the bullet will be 1.2 light years "away" from you - by your measurement, adding up the 0.6 light years I moved away from you and the 0.6 light years the bullet moved away from me.

However, just as you added up the distances, you have to add up the times, too - the bullet doesn't get there, from your point of view, until 1 year (how far I went into the future) plus 0.3 years (how far the bullet went into the future relative to me), or a total of 1.3 years "in the future", using your definition of "future". It won't actually make it to 1.2 light years away from you until 1.3 years into your future.

1.2 light years per 1.3 years is still slower than the speed of light, about 0.9c. So, if I'm moving at 0.6c "away" from you (using your definition of "away"), and I fire a bullet at 0.6c "away" from me (using my definition of "away"), it will only be moving at about 0.9c "away" from you (using your definition of "away), not at 1.2c.

This would be easier to explain with a diagram, but hopefully I've provided enough information to let you create your own diagram.

What if I fire the bullet faster? As long as I don't fire it faster than light, relative to me, it turns out it won't be going faster than light relative to you, either.
[ August 04, 2004: Message edited by: Warren Dew ]
 
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[Joseph George]: Let me take a stab at Heinsberg:

He's the guy who established that it's impossible to simultaneously know both the speed and flavor of the ketchup while it's still in the bottle, right?
[ August 05, 2004: Message edited by: Jim Yingst ]
 
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Originally posted by Jim Yingst:
Let me take a stab at Heinsberg:

He's the guy who established that it's impossible to simultaneously know both the speed and flavor of the ketchup while it's still in the bottle, right?



If you mean Heisenberg's uncertainty principle...
yes, or rather that it's impossible to know the one without changing the other.
It's a similar situation to the Schroedinger cat paradox.

As to the speed of light, it is an incorrect assumption that speeds higher than the speed of light are impossible.
The only speed that is impossible to achieve by anything that has mass is the speed of light itself.
Current science doesn't have the answer as to how this could be achieved but does not rule out the possibility.

When travelling at .6c and releasing something which accellerates away that something will need to apply the same thrust you are applying to achieve the same accelleration (if it has the same mass).

In your scenario, A can only achieve about half the accelleration it could without the mass of B.
After untethering B it will therefore accellerate away and B will be left to play catch up.
Remember that in vacuum speed is limited, accelleration is not. You now have 2 vehicles of identical mass (or rather A will have less mass than B because it has less fuel unless you assume a means to achieve thrust without expelling anything and therefore have higher accelleration) which can achieve identical thrust.
That means they can also achieve identical accelleration (if they carry the same mass in fuel of course).
Top speed in vacuum is limited only by the amount of thrust applied over time per kilo of mass (not weight). As both ships will have the same mass of fuel (thus the same number of KN of thrust) to expend they'll end up at the same speed (in a theoretical situation, in your supposition B would achieve a higher speed because A was held back by Bs mass and B has a jumpstart).

As speed increases the amount of KN needed to increase speed further goes up asymptotically, reaching infinity at lightspeed.
As a result accelleration decreases asymptotically to 0 as lightspeed is approached without increasing thrust.

Ergo, nothing can go faster than light without having more than infinite thrust available and the top speed that can be achieved is dependent on 3 factors:
1) mass of the vehicle without fuel
2) mass of fuel (or rather amount of stored energy)
3) thrust of the engines

The thrust (together with mass of vehicle and fuel remaining) determines the point where the increase in required energy to accellerate further is larger than the amount of energy that can be produced.
The amount of fuel in KN determines how much thrust can be produced which can limit the top speed to something under the upper limit defined above.

Once that speed is achieved it will in an ideal vacuum away from bodies exerting force on it continue indefinitely at that speed.
Planets and stars (and even interstellar dust) will of course exert forces which will change the velocity and path of the vessel, eventually trapping it in a gravity hole around a star or in a sink where gravitational forces even out if it happens into such an area at near 0 speed.
[ August 05, 2004: Message edited by: Jeroen Wenting ]
 
Joe King
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Thanks everyone, that's cleared up a lot! Some very interesting replies so far.

The one that is the hardest to understand is the Potential Energy problem. I've always thought that this was a bit of a cop-out - a theory used to plug a hole, but not really completely matching it, a bit like bunging a square peg in a round hole to keep out some leaks.

It does make a kind of sense that in picking something up I could be adding energy to it (the spring pulling example above was quite good), but what about objects that have not been picked up? Imagine an asteroid trundling through the galaxy which happens to come near to the solar system. Its likely that the sun will alter the course of the asteroid as it goes past. In this case, the asteroid has not been pulled up from the sun so the "spring" analogy doesn't quite match. In this case, where does the energy come from to move the asteroid? Fred said :


The energy is already IN the rock. It's called Potential Energy (PE). It's stored, waiting to be released, just like gasoline has potential energy, released if you light it and provide Oxygen. There is something preventing the PE from being converted to Kinetic Energy (KE) - the ground or your hand. Remove that, and it falls.


If I understand it correctly, when the energy in some gasoline (/petrol ) is released the gasoline is reduced - there isn't as much of it around afterwards because some of it has been released as energy, and some has been transformed as part of the reaction. If the rock has PE stored inside it waiting to be released, then that seems as if something in the rock is reduced when this energy is released. This is the fundamental thing which confused me - one lump of matter seems to be able to exert forces upon all other passing lumps of matter without ever being reduced or having its ability to exert the force reduced. Why has everything got a never ending supply of gravity?! (It would make a lot more sense if things decreased in mass as they exerted gravitation force upon things)

Now, bonus points if someone can tell me what the universe was like 3 seconds before the Big Bang My personal theory was that just before the Big Bang there was a very bored work experience person saying something along the lines of "I wonder what this big red button does?".
[ August 05, 2004: Message edited by: Joe King ]
 
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Originally posted by Joe King:
It does make a kind of sense that in picking something up I could be adding energy to it (the spring pulling example above was quite good), but what about objects that have not been picked up? Imagine an asteroid trundling through the galaxy which happens to come near to the solar system. Its likely that the sun will alter the course of the asteroid as it goes past. In this case, the asteroid has not been pulled up from the sun so the "spring" analogy doesn't quite match. In this case, where does the energy come from to move the asteroid?



This energy comes from the big bang. The big bang "winds up the spring" to setup the distance between massive objects (potential energy stored in the curved space-time). The further evolution of the universe converts the energy to different forms and increases the entropy in the process. Of course, it is much more complicated than I made it sounds like.

Also, you might ask: The where does the energy of big bang come from? The answer is that at the beginning of the big bang, the physical conditions are so extreme that the law of energy conservation is not longer true ...
 
Ashok Mash
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Originally posted by Joe King:
Now, bonus points if someone can tell me what the universe was like 3 seconds before the Big Bang



Excellent question. This is why I don't really believe Big Bang was the start of everything. A big bang might have happened but then what was there there before the Big Bang!! As per inflationary theory Universe is flat and its going to expand forever! But it�s expanding in where? Isn�t that space also part of this universe, by definition? And when they say Universe is flat, how can they be sure? Isn�t that a bit like �Earth is flat� all over again?
 
Jeroen Wenting
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As there was no time before the Big Bang, the question has no meaning.

Indeed there are physisists who question the BB theory and are thinking of other scenarios that may explain the observations.
 
Michael Yuan
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Originally posted by Ashok Mash:
But it�s expanding in where? Isn�t that space also part of this universe, by definition? And when they say Universe is flat, how can they be sure? Isn�t that a bit like �Earth is flat� all over again?



The universe is expanding in the sense that the total volume of the space is increasing. Note that although the universe might have a finite volume, it does not imply it has a boundary in the 3-D space.

When they that the universe is flat, they have solid observational evidence. It is very different from saying that the earth is flat.
 
Michael Yuan
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Originally posted by Jeroen Wenting:
Indeed there are physisists who question the BB theory and are thinking of other scenarios that may explain the observations.



Not these days. I do not think you can explain the new COBE observations of the highly uniform microwave background without some sort of BB. That was one of the defining scientific observations in the late 90's that put away most people's doubts about BB. Of course, people disagree *how* BB had happened.
 
Ashok Mash
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Originally posted by Jeroen Wenting:
As there was no time before the Big Bang, the question has no meaning.




There�s another theory baking in the owen at the moment, a possible �Big Splat� before the Big Bang. Apparently, its based on M-theory (Strings and all that) and according to them (link) everything takes place in a five-dimensional universe and before Big Bang there was two perfectly flat four-dimensional surfaces!!! Now they are talking about a possible parallel universe too!!
 
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I always wondered -- if I pause briefly as I type this sentence, does it change the future?
 
Jeroen Wenting
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the collective actions of all living and dead things define the future so your short pause will indeed cause the future to be different from the future there would have been had you not paused at all.
Whether that difference is profound enough to have any significance is another question.

For example[political stuff snipped]
[ August 05, 2004: Message edited by: Max Habibi ]
 
fred rosenberger
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I doubt your delaying a message in these forums will have any such effect


and yet a butterfly flapping it's wings in China...

as to what happend before the Big Bang... I remember Stephen Hawking saying this question makes no sense. Time is a dimension, just like the other three we're more familiar/comfortable with. The Universe HAD no height, width or depth before the bang, AND no TIME. time didn't exist. so there was no "before".

Now, i'm pulling this from some random story/blurb i read proably 8 years ago, and may not be remembering it exactly right. Plus, Steve may have changed his mind or just plain been wrong.
 
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Originally posted by John Smith:
I always wondered -- if I pause briefly as I type this sentence, does it change the future?



A different perspective... If the future. by definition has not happened yet... how can it be changed?
 
Bacon
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Originally posted by Jim Yingst:
Let me take a stab at Heinsberg:

He's the guy who established that it's impossible to simultaneously know both the speed and flavor of the ketchup while it's still in the bottle, right?



Ketchup defies all physical laws, it is always too slow and tastes exactly the same as it always has. The predictability quotient is 100%
 
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This is the fundamental thing which confused me - one lump of matter seems to be able to exert forces upon all other passing lumps of matter without ever being reduced or having its ability to exert the force reduced. Why has everything got a never ending supply of gravity?! (It would make a lot more sense if things decreased in mass as they exerted gravitation force upon things)

Einstein talks about the distortion of the space-time continuum created by gravity. Imagine a rubber sheet that you place a bowling ball on. Now roll a marble across the sheet so it passes by the bowling ball. The marble will change it's course as it moves across the deformed rubber sheet. Did the bowling ball exert anything on the marble? Or did the marble simply move through space and have its course changed by the deformation of space? Quantum physicists like to talk about there actually being a force betwen the bowling ball and marble that is mediated by a particle (graviton). This fits in with the other forces such as the strong force and electromagnetic force that are mediated by particles. Gravitons have never actually been detected.

I should add that when we are talking about an exchange of particles, the particles are actually "virtual" particles. This has to do with Heisenberg's uncertainty priciple and perturbation theory which allow a system to violate the conservation of energy as long as it happens so quickly that it can't be detected. There is no enrgy cost to a system to exchange virtual particles.
[ August 05, 2004: Message edited by: Thomas Paul ]
 
Thomas Paul
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I read a book recently where the author makes the argument that intellignece could not exist in a universe that did not have three spatial dimensions and one time dimension. A universe with more than one time dimension would be unintelligible because there would be no causality. We could never learn from our actions in such a universe because cause would not lead to effect.
 
Jim Yingst
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[JG]: Let me take a stab at Heinsberg:

[JY]: He's the guy who established that it's impossible to simultaneously know both the speed and flavor of the ketchup while it's still in the bottle, right?

[JW]: If you mean Heisenberg's uncertainty principle...
yes, or rather that it's impossible to know the one without changing the other.


I suspect some context may have been lost in the quoting process, so let me clarify: Joseph was the one referring to "Heinsberg" rather than "Heisenberg". My reply was a joke based on the fact that there's a brand of ketchup called "Heinz", with commercials that refer to the velocity of the ketchup in the bottle. ("Anticipation...") I wasn't actually asking a serious question here; I know about Heisenberg's uncertainty principle.
 
Bacon
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Originally posted by Jim Yingst:
I know about Heisenberg's uncertainty principle.



Are you certain?

---

Another equally important part of the Heisenberg uncertianty principle is that you cannot observe something without changing it. Poorly quoted, I know. This opposes the Heinzberg certainty principle, which states that no matter how long you observe the end of the ketchup bottle, nothing will happen unless you use a butter-knife.

On the subject of gravity. It is an aspect or character of matter. It is not contained in matter. Unless you are referring to ketchup, upon which gravity has no effect.

For a more intelligent explanation of The Heisenberg Uncertainty Principle see this link... http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/quantum/heisenburg.html
[ August 05, 2004: Message edited by: Ray Marsh ]
 
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New Scientist - Big Bang was more like a deep hum

Listen to the audio. Disappointing, eh?

Consider that 8 1/2 years of sound energy is needed to heat a single cup of coffee and nobody has been killed by thunder. Yet! AFAIK.
[ August 05, 2004: Message edited by: Helen Thomas ]
 
Jim Yingst
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[Ray Marsh]: Are you certain?

Absolutely. Which of course means I am therefore totally unable to explain it or apply it in any useful way.
[ August 05, 2004: Message edited by: Jim Yingst ]
 
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> My reply was a joke based on the fact that there's a brand of ketchup called "Heinz", with commercials that refer to the velocity ...

This is so tragic I am so sorry i arrived few minutes (which i used to think over if he really meant Heinz or not) too late to save Jim from this self-explanation ...
 
Bacon
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Originally posted by Jim Yingst:
[Ray Marsh]: Are you certain?

Absolutely.



So... just to be clear... you are certain about uncertainty, right?

... Which of course means I am therefore totally unable to explain it or apply it in any useful way.



I'm not certain there is a useful explanation or application. Quantum physics is mostly theoretical.

Suggested reading for anyone interested in quantum physics. I haven't read it yet, it is on my short list of books to read. A colleague of mine, who is much smarter than me, said that it made him feel stupid. So if you're having a problem with an inflated ego, give this book a spin.

The Universe in a Nutshell, Stephen Hawking
[ August 05, 2004: Message edited by: Ray Marsh ]
 
Jim Yingst
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[RM]: So... just to be clear... you are certain about uncertainty, right?

Yes, that was the intended joke.

I'm not certain there is a useful explanation or application. Quantum physics is mostly theoretical.

Actually quantum physics has had a huge number of applications, affecting our day-to-day lives far more than, say, relativity. E.g. it allows us to predict and control the electrical properties of semiconductors, which are used extensively in computers. Much of chemistry is based on how electrons interact when two different atoms get near each other - this is determined largely by quantum electrodynamics. It's pretty useful stuff, really.
 
Warren Dew
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Ashok Mash:

There�s another theory baking in the owen at the moment, a possible �Big Splat� before the Big Bang. Apparently, its based on M-theory (Strings and all that) and according to them (link) everything takes place in a five-dimensional universe and before Big Bang there was two perfectly flat four-dimensional surfaces!!! Now they are talking about a possible parallel universe too!!

Heh. Let's hear it for loop quantum gravity.
 
Jeroen Wenting
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Originally posted by Jim Yingst:
[QBI suspect some context may have been lost in the quoting process, so let me clarify: Joseph was the one referring to "Heinsberg" rather than "Heisenberg". My reply was a joke based on the fact that there's a brand of ketchup called "Heinz", with commercials that refer to the velocity of the ketchup in the bottle. ("Anticipation...") I wasn't actually asking a serious question here; I know about Heisenberg's uncertainty principle. [/QB]



Maybe Max no longer allows the word Heinz because it can have political meaning?

I'm not certain though...
 
Joe King
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Originally posted by Michael Yuan:

This energy comes from the big bang. The big bang "winds up the spring" to setup the distance between massive objects (potential energy stored in the curved space-time). The further evolution of the universe converts the energy to different forms and increases the entropy in the process.



I like the sound of this idea, it seems quite elegant.

I wonder if it would be possible to create a mini-bang ie if we were able to compress (somehow) a bunch of matter into a small enough space, if we could create something with similar conditions to the blob that the big-bang came out of. The problem is the "bang" aspect of this of course.
 
Joe King
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Originally posted by John Smith:
I always wondered -- if I pause briefly as I type this sentence, does it change the future?



Well if that isn't a can of worms, nothing is.

If you think that determinism is true, then every thing that happens in the universe is determined by the configuration of the universe the moment before hand (a kind of "clockwork universe"). By this theory, if you could magically pause the universe and make a copy of it, and then set the two copies running again, the same things would happen exactly the same in both. Unfortunately (for our egos) if this were true then it would kind of negate the idea that we have any kind of free will. There are two possible spanners in the works of this idea though - it assumes that the universe is a closed system, and there are also the new quantum physics theories that seem to suggest that there are some random events that occur.

Personally I find it hard to see how the universe could not be a closed system, although I don't discount the possibility (I'm very aware of my own (and everyone else's) ability not to fully understand these matters). As for quantum physics... well there's probably only a handful of people who can, at best, fully realise how little they know about it.

I suspect that however much we learn about the universe, its just far too complex and vast for us to understand - every time we answer a question, another dozen questions appear. Its probably a good thing really - think of all the trouble the scientists would get up to if they got bored.
[ August 06, 2004: Message edited by: Joe King ]
 
Helen Thomas
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Perhaps ketchup would come to mean more than Heinz. There is a George Washington Ketchup marketed recently as W. Ketchup. The lady-in-waiting only owns about 4% of Heinz stock.
 
Bacon
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JY: Yes, that was the intended joke.



Sorry, I have a bad tendency to take a joke too far and then tell it three more times just to make sure that its still not funny anymore. Hey, we can't all be Ray Ramano! "Everybody Love Raymond" There's just something about that title.

RM: I'm not certain there is a useful explanation or application. Quantum physics is mostly theoretical.

JY: Actually quantum physics has had a huge number of applications, ... It's pretty useful stuff, really.



I didn't know that. Most of the stuff I've read has been of a theoretical nature. Certainly I am not well read, just enough to get myself in trouble. When Hawking starts talking about 10 dimensional string theory, it makes my head hurt and then I need to go watch SpongeBob SquarePants for a while to make it stop.
 
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