Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[dreiche2]

There's no arbitrary limit to the car's speed, either along the road or along the Earth.

Yes there is, the speed of light. That has nothing to do with friction.

In space, however, you're all in the same boat. Two cars moving 200 kps away from each other will each perceive the other's speed as 400 kps.

No, that's not true, although the effect only becomes visible when you approach relativistic (relative) speeds.

At lightspeed [...] their speed relative to each other will still be their speeds combined.

No. Welcome to the world of special relativity.

At lightspeed, both cars will disintegrate and become energy waves,

And of course nothing disintegrates either, because you cannot reach the speed of light.

I mean, really, consider it. The fact that you're moving at .5c in one direction and the car is accelerating to 1c in another won't make the car disintegrate at .5c just because it's travelling at 1c for you.

That's because it wouldn't be travelling at 1c for me.

ninja-edit: alright, simultaneity. But why take an illogical theory as a base? With the amount of holes you have to plug using time dilation and length contraction, even dissimultaneity, is it not easier to assume that speed of light is just constant, pronto? Use alternative theories to explain time dilation, for example I harbor a theory that matter as it is is simply energy weaved into a pattern. Chunks of energy moving at relativistic speeds, or spinning, as it were, make particles. Have an object move at a significant speed, and ambient energy of the universe will begin to affect the matter, just like air would affect an open mechanical clock, slowing it down. It's all very sketchy, since I lack the dedication to sit down and attempt to make sense of it, god forbid actually write it down, but it also seems consistent. Thinking up clauses and thinking up solutions to them is one of my favorite pastimes when I want to rest.

It's not a illogical theory, it's just UNintuitive*. And, I already tried to point out that things like time dilation don't plug the holes, but follow naturally as predictions of the two underlying axioms.

You do not understand what the theory says, nor its implications. You can say you don't believe it because the implications are mind boggling, and you don't have to understand the theory itself to do that, but at the very least you have to understand the implications, i.e. what the theory actually says what happens in this or that situation.

I guess I made my points. I didn't actually want to argue here, just explain, but now it's up to you really. I look forward to Sean Mirrsen invalidating a century of modern physics with theories conceived in his spare time though 

*Edit: corrected 'Freudian slip', thanks Il Palazzo

[Sean Mirrsen]

I'm not arrogant, at least I don't think I am.

I'm not talking down on other theories, I'm seeking to make mine suit experimental evidence.
(also, in the russian roulette example, logic agrees with math and physics, and tells me that pulling the trigger would a very bad idea. And experimental evidence can be obtained by, say pointing the thing at the other guy.

I say, let theories exist as long as they work, but it's always possible to arrive at perfectly consistent and inter-agreeing results if the basic source material is wrong. It's like Sudoku. You may place one wrong number and keep filling the table until you're down to two unfinished rows, and then realise you've made a wrong assumption at the beginning and have to start over.

I'm perfectly fine with special relativity and stuff, but if I make an FTL jumper in my garage, I will expect no less than ten times its market cost if the world's scientific community decides to buy it from me.

[shadow_slicer]

About the negative mass again, it is merely a different way of looking at antimatter.  It behaves exactly as standard theories of antimatter, but is simpler, and therefore, by Occam's razor, I prefer it.

I cannot remember where I read it.  Probably 'A briefer history of time.', by Stephen Hawking.  It was a possible explanation of virtual particles.  The electron and positron appearing and then annihilating, but with no energy input or output, could be viewed as an electron traveling forward and backward in time along different paths.

After looking at Wikipedia, I can understand why you might think that antimatter has negative mass. Current experiments have been able to show that they have either opposite charge or negative mass (but not both), but these two scenarios are only equivalent in that class of experiment, and behave completely differently in other cases. As I've said, negative mass seems (at least to me) to imply negative energy, which is known to be untrue (based on conservation of energy analysis of the collisions that constructed them). Additionally, they have shown that positrons are electrically attracted to electrons, which seems to contradict the negative mass theory. Wikipedia does seem a little less certain about this issue, but the physics seems a lot simpler if antimatter has positive mass.

There's no arbitrary limit to the car's speed, either along the road or along the Earth. All that matters is its speed relative to air, which resists its motion. An orbital observer seeing the car move along with Earth will see it move faster, but it'll have no meaning.

There's no arbitrary limit to speed in space either. You can accelerate as much as you want, and you can always go faster. From your perspective, your speed will approach infinity (though light will always go faster!).

In space, however, you're all in the same boat. Two cars moving 200 kps away from each other will each perceive the other's speed as 400 kps. At lightspeed, both cars will disintegrate and become energy waves, but their speed relative to each other will still be their speeds combined. It makes no sense for the general point at which what I call "space friction" will turn matter back into energy to differ based on your speed relative to the object. I mean, really, consider it. The fact that you're moving at .5c in one direction and the car is accelerating to 1c in another won't make the car disintegrate at .5c just because it's travelling at 1c for you.

I'm not sure where you're getting the "disintegrate and become energy waves" part from. Of course I haven't read anything that detailed what happens to mass-bearing objects if they somehow manage to accelerate to the speed of light (since that is impossible anyway). Instead let's look at a scenario where something is going a substantial portion of the speed of light.

Imagine you have two objects moving opposite directions away from you at 0.75c. You can still see both objects since they are going less than the speed of light relative to you. They can also still see you since the light from you can catch up to them. If we were calculate relative velocity your way, the relative velocity between the two objects is 1.5c. This means that any light coming from one of them could never reach the other. But since you can see them, and they you, you could act as a relay and send messages from one object to the other. But since there's no real difference in speed between your relayed signal and the original signal, the two objects must be able to see each other. This creates a contradiction. You can't calculate relative speed that way.

ninja-edit: alright, simultaneity. But why take an illogical theory as a base? With the amount of holes you have to plug using time dilation and length contraction, even dissimultaneity, is it not easier to assume that speed of light is just constant, pronto? Use alternative theories to explain time dilation, for example I harbor a theory that matter as it is is simply energy weaved into a pattern. Chunks of energy moving at relativistic speeds, or spinning, as it were, make particles. Have an object move at a significant speed, and ambient energy of the universe will begin to affect the matter, just like air would affect an open mechanical clock, slowing it down. It's all very sketchy, since I lack the dedication to sit down and attempt to make sense of it, god forbid actually write it down, but it also seems consistent. Thinking up clauses and thinking up solutions to them is one of my favorite pastimes when I want to rest.

The theory is not really illogical, it just implies some strange things. If you look at the mathematics behind it, it is very neat and elegant. This theory is very well supported, and if it was wrong, things like GPS would not function (since GPS satellites have to account for time dilation due to their orbital velocity in order to maintain precise time). Additionally, particle accelerators have shown us that particles moving at higher speeds decay at a slower rate (precisely according to theory!). In short, time dilation is something that has been observed to occur. If you can find an alternative theory capable of explaining both time dilation and a constant speed of light for all observers, consistent with known results, by all means quit your job and publish it so you can win the Nobel prize.

[Il Palazzo]

(also, in the russian roulette example, logic agrees with math and physics, and tells me that pulling the trigger would a very bad idea. And experimental evidence can be obtained by, say pointing the thing at the other guy.

See, you value what you consider logic very highly. Only it's not really logic, but common sense. It's your everyday experiences painting your perception of what's "logical" and what's not, while the proper naming would be "intuitive", or not.
In the above example, if you've never seen, or heard about, or had a revolver, and you never bothered to learn to count to six, then you wouldn't have the intuition to decide if you are about to die.
It's the same with relativity, it's not illogical because it doesn't agree with your common sense, it's just unintuitive, as dreiche was trying to say but failed due to Freudian slip.

[Sean Mirrsen]

I don't have a job. But yeah, things like operational GPS and slow-degrading particles are harder to justify with simple things. I'll have to think about it. Thanks for the idea!

And Il Palazzo, if I never saw a revolver, would not know what it does, and would not be told what the game is about, then yes, I would happily keep pulling the trigger like the mindless drone that I would have to be. I would have likely just as happily do it with a semiautomatic Beretta or an AK-47. If I didn't read so much Wikipedia, didn't have a casual interest in physics and astronomy, and didn't watch Discovery Channel, I wouldn't have any intuition to judge these sorts of physically odd things either. But it so happens that I have the intuition, and it tells me these scientifically heretical things. I'm just trying to make sense of the universe.

[dreiche2]

Well, well.

And because I feel like giving big, mania induced speeches: Here's a tip for that theory you're going to develop:

If you want to understand the universe, you need to let go of your intuitions. Intuitions and concepts in your brain have been formed by evolution to be useful for survival in the everyday world. Once you try to describe things outside everyday life, there's no reason your intuitions should still be true.

The dissolving of intuitions seems to be at the heart of scientific progress in the last millennia. It starts with finding the world is round, not flat (BUT what about the people in China, hanging upside down??); then continues with the realization that, literally and figuratively, the universe does not revolve around our world. Nor does our own world revolve around humanity, in that we are not qualitatively different from other animals, as the theory of evolution has shown.

Then special relativity came along and showed us that even our concepts of space and time might be inherently flawed, shaped by what happens in our slow-velocity everyday world. And then, quantum mechanics... well, nobody really understands quantum mechanics (yet?). But it further shakes the foundations on the basis of which we try to understand reality, down to what it means to say a "thing" exists.

And where physics will challenge our intuitions from the outside, advances in Neuroscience and Artificial Intelligence will challenge them from the inside, and this is where I hope to contribute. What is perception? What does it mean to have a self? (hint: not much). Not much will remain of what you think is intuitive. Then again, Buddhism showed the way thousands of years ago.

Alright girls, I'm done here, I have to get back to playing cards with Einstein and Buddha.

"How are you guys?"

Einstein: "I'm relatively fine."

"Very funny, Albert"

Buddha: "He's so funny, I could forget mySELF".

"Guys, shut up or I'll put you back into the freezer!"

[decius]

First, a comment on "logical". Some of us are using it to mean "intuitive", some are using it to mean "accurate" and some of us are using it to mean "in accordace with the rules of logic".

First, the premise of relativity: "The speed of light in a vacuum is always a constant with respect to any given observer." This means exactly the same thing as "The speed of light in a vacuum is constant with respect to all observers." ALL of relative physics assumes this to be true without evidence of any kind whatsoever. It remains listed as a postulate.

The implications of a constant c are time/space distortion, absolute speed limits, and the like.


As for the higher math, let's review the properties of the extended real number system. It consistes of the real number system, plus either one or two points at infinity. For simplicity, I will focus on the system with two points, but limit myself to nonnegative numbers. I don't have access to a math typeset, so I will put everything in spoken form.

Brief overview of limits at infinity, infinite limits, and "continous at infinity": The limit at infinity is the same as the real number definition. If I say "the limit of f(x) as x approaches infinity is a" I mean "there is some b for which "if x>b, then |a-f(x)| < |c| for any nonzero c."" To say the limit is infinity means that there is some value of b for which if x>b, f(x)>c for all real c.

In briefer terms, I can get as close to the limit as I want, but not neccessarily reach the limit.

To say that a function is continous (on an interval) means that the limit of the function is equal to the value of the fuction on every point in that interval. That is to say, the point the function approaches is reachable at that point. A function that is undefined at a point is not continous on any interval containing that point.

Frankly, if you do not understand the behavior of limits better than I just explained it, you don't have the background to understand behavior at infinity.

Addition and multiplication not involving zero are continuous at infinity. That is to say, the limit as x approaces infinity of a+x and of a*x for x =/= 0 is equal to the value of x plus infinity or x times infinity. Most functions that are continous for all real numbers are continous at infinity. Divison, while continous at infinity, is NOT continous for all real numbers. Division by zero is undefined, and remains undefined. |x+2|(x+3)/|x+2| remains undefined for x=2 in the extended real number system. The form 0/0 remains inconclusive, and the form a/0 (for a=/= 0) remains undefined, but a/infinity and infinity/a ,(for a>0) are equal to 0 and inifinity, respectively.

Important note: This discussion pertains to math, only. No physical quantity that exists can ever be equal to infinity or zero. MOST physical quantities are not well-behaved approaching zero; that is the basis of quantam physics and molecular chemistry.

[dreiche2]

If I say "the limit of f(x) as x approaches infinity is a" I mean "there is some b for which "if x>b, then |a-f(x)| < |c| for any nonzero c."" To say the limit is infinity means that there is some value of b for which if x>b, f(x)>c for all real c.

It should be, for any given c, you find a b such that f(x) > c for all x > b, no? Your formulation seems at least confusing, as I read it as: There is a b such that f(x) > c for all x> b and all c, depending on what "for any c"/ "for all real c" refers to.

Addition and multiplication not involving zero are continuous at infinity. That is to say, the limit as x approaces infinity of a+x and of a*x for x =/= 0 is equal to the value of x plus infinity or x times infinity.

I don't remember doing much with the extended real numbers apart from using them for notation reasons, or maybe something with projective spaces, but  a+inf = inf, not a+inf = a+inf, as you stated, right (in the limit or not)? Nor am I sure I understand what you mean with "addition" is continuous... addition is not a function on the real numbers, but on tuples...

Most functions that are continous for all real numbers are continous at infinity.

That should only apply for functions that either go asymptotically towards a constant, or asymptotically to infinity, yes? (E.g. sinus is not continuous at infinity; exp(x)  * sin(x) isn't either, although it is unbounded. Nor is |sin(x) * exp(x)|, although this one is even bounded from below additionally.. hey, I'm just wondering...)

[Sean Mirrsen]

Well, well.

And because I feel like giving big, mania induced speeches: Here's a tip for that theory you're going to develop:

If you want to understand the universe, you need to let go of your intuitions. Intuitions and concepts in your brain have been formed by evolution to be useful for survival in the everyday world. Once you try to describe things outside everyday life, there's no reason your intuitions should still be true.

The dissolving of intuitions seems to be at the heart of scientific progress in the last millennia. It starts with finding the world is round, not flat (BUT what about the people in China, hanging upside down??); then continues with the realization that, literally and figuratively, the universe does not revolve around our world. Nor does our own world revolve around humanity, in that we are not qualitatively different from other animals, as the theory of evolution has shown.

Then special relativity came along and showed us that even our concepts of space and time might be inherently flawed, shaped by what happens in our slow-velocity everyday world. And then, quantum mechanics... well, nobody really understands quantum mechanics (yet?). But it further shakes the foundations on the basis of which we try to understand reality, down to what it means to say a "thing" exists.

And where physics will challenge our intuitions from the outside, advances in Neuroscience and Artificial Intelligence will challenge them from the inside, and this is where I hope to contribute. What is perception? What does it mean to have a self? (hint: not much). Not much will remain of what you think is intuitive. Then again, Buddhism showed the way thousands of years ago.

Alright girls, I'm done here, I have to get back to playing cards with Einstein and Buddha.

"How are you guys?"

Einstein: "I'm relatively fine."

"Very funny, Albert"

Buddha: "He's so funny, I could forget mySELF".

"Guys, shut up or I'll put you back into the freezer!"

Intuition tells me a lot of things, but humor tells me Einstein could just as well be an alien agent sent to impede our scientific progress. His postulate, while reasonably close to any truth that might exist, allowed us to make calculations and come to reasonably true results, at the same time limiting our outlook and forcing us to come up with ways to overcome imaginary barriers imposed by science. That's humor. Intuition tells me that it's wrong to base everything you know on something that, despite all the calculations and matching results, might still be wrong in something.

I took a little walk through the cold and thought up what seemed like a witty comparison. Current science obtained the Ultimate Answer in form of the relativity theory, and proceeded to ask itself many questions to match the answer, searching for the key to the Universe.
To me, it seems that asking many questions and sifting through answers until you arrive at the Ultimate one is the proper way of doing it - at least then you have an answer that fits every question you ask.
Make what you want of my attempt at being witty, I just thought it up and wanted to share.

I realised I actually tried to explain increased particle longevity to myself at some point, but gave up because it led me into such convoluted areas of existence that my lore failed me completely. Specifically, I can't explain relativistic particle longevity without explaining the structure of the particles and their interaction with ambient energy, and I just have no definite knowledge of particle specifics. The explanation would have to include stuff like electric charge, atomic forces, and gravity, because in the theory they're all interlinked.

I tried to explain GPS satellite positioning accuracy with just acceptable inaccuracy thresholds, but a difference of 300km/s (the assumed maximum combined total of Earth's orbital velocity and the Sun's orbital velocity) makes for a 24km inaccuracy range at 20.000km altitude, and that won't work even if the 0.08s of time difference would be autocorrected client-side. Idea requires more thought. Time dilation on the satellites themselves can be explained by the same handwavy "space friction" that I've yet to pinpoint.

[Il Palazzo]

...

Anyway. I believe I asked this in one of the physics-related threads that popped up sometime in the past on this forums, but I don't recall getting a meaningfull answer.
So, is anyone able to explain to me the twins paradox? The guy who taught me physics relegated me to some book that I've never picked up, and I still can't wrap my head around it. Apparently it's somehow resolved during the actual acceleration, or maybe the reversing of movement direction that the ship would have to do at some point, to get back to the point of origin.
I can take some algebra, somewhat less of calculus, if you need to use it, but qualitative explanation would be enough.

[dreiche2]

Intuition tells me that it's wrong to base everything you know on something that, despite all the calculations and matching results, might still be wrong in something.

Oh, yes. It's not about special relativity being the absolute truth. It's probably wrong, or at least incomplete, or a limiting case, as relativity and quantum mechanics have yet to be married without trouble. Much as Newtonian physics was a limiting case of relativistic physics (for the limits mass and velocity to zero). The point is that special relativity is the best theory there currently is to explain certain known phenomena. And you don't seem to have a good alternative either (yet?). Which doesn't mean there doesn't exist one.

Science is not about finding true descriptions of reality, it's about finding better (more complete, simpler) descriptions than whatever currently exists.

What is surprising is that you seem to think that you can up with a better explanation just like that, all while you apparently haven't really tried to understand the explanation that already exists.

These things are complicated. The world is complicated. Things are difficult. You probably wouldn't just sit down and think, hey!, I will compose a better symphony than Beethoven! I will design a better space ship than NASA!

But to come up with a better theory of the universe? No problemo!

[Sean Mirrsen]

The Beethoven case, no. I'm terrible at music. To quote a certain someone being compared to DaVinci, "Absolutely ridiculous, I don't paint.". The NASA thing, on the other hand... well, I've never tried, and with my worldview taken into account I'll probably take bloody long if I do try (having experimental evidence on each tested part, for example, as opposed to just calculations). I'm also not a rocket scientist. But all in all, I have a basic idea of what it's like to go into space, so...
First things first, it will not be a goddamn rocket. I will not attempt to design a spaceship until I have designed and built its prerequisites - namely, a compact reliable powersource, and efficient propulsion systems operating on electricity alone. Glorified firecrackers is NOT something I can consider a good way to travel anywhere. And they damage the ozone layer. This may seem like oversimplifying the task (you have to agree, even NASA can build a good spaceship with those), but anything else is too unstable, and too inefficient.

[bjlong]

Sean: Some basic experimental evidence can be derived from two sources: The Michelson-Morley experiment and the amount of muons at the surface of the earth.

To sum up the evidences: The Michelson-Morley experiment used a very accurate device for measuring the speed of light that could rotate. By rotating the apparatus, if the speed of light was not constant, they could detect the motion of the earth by the differences in the speed of light. They did not detect any differences, save for some experimental errors. Furthermore, more accurate devices have been constructed and found that the differences are so small as to be miniscule.

The Muon decay evidence is somewhat more elegant, and is based on well-established measurements of amounts of muons at sea level. With length contraction, the math tells this story: Cosmic rays enter the upper atmosphere, and break nuclei into pions. The pions then rapidly decay into muons, which have a high velocity earthward, generally. Because of length contraction, the math says that the muons can penetrate deep underground before decaying, which we regularly observe.

If we throw out length contraction, then the cosmic rays can only break down a short distance above our heads, to the point where airplanes would receive cartoonishly high doses of cosmic rays. I'm talking dead-after-a-flight amounts. And, clearly, the airlines employ many people for more than a flight, so you'll have to work around that one.

There are a lot more things to relativity, especially general relativity, that make the theory worthwhile, such as the bending of light near a gravity well.

[DreamThorn]

I just lost an incredibly long post.  And I see I have been ninja-ed on the Michelson-Morley experiment, which I have done in a practical class.  We set it up and took the measurements and everything.  We also learned about the muon decay.

Since I'm going to go sleep now, I'll just give one-liners:

The Michelson-Morley experiment is older than relativity.  It inspired many scientists to look for a new theory, and Einstein found it.

Cheap, no-pollution space travel requires the construction of a space elevator.  To move between the planets you can use ion drives, plasma drives or solar sails.

Physics (and some other sciences) is all about predicting the future accurately, not explaining the workings of the universe.  Explaining the universe is just a way to make the maths more intuitive.

The twins paradox stops being a paradox when acceleration (the change in direction) is taken into account.  Acceleration speeds up the relatively traveling twin's time-flow (because of the direction of the acceleration), so they will be the same age when they get back together.

[Il Palazzo]

The twins paradox stops being a paradox when acceleration (the change in direction) is taken into account.  Acceleration speeds up the relatively traveling twin's time-flow (because of the direction of the acceleration), so they will be the same age when they get back together.

Thanks, but I knew that much, as you should be able to gather from my question. I need an answer that would give me an intuition to understand the thing.