Light Speed?

[stringyquark]

Relativity always hurts my brain! Especially when I think of the LHC.

I am a proton, I'm in the LHC doing 95% the speed of light. My buddies are protons, there in the LHC, there doing 95% the speed of light, And it's coming right at me.

So we're closing the distance between ourselves faster then light, but we're not.

Oh no, here comes the headache.

[SolarLiner]

Relativity always hurts my brain! Especially when I think of the LHC.

I am a proton, I'm in the LHC doing 95% the speed of light. My buddies are protons, there in the LHC, there doing 95% the speed of light, And it's coming right at me.

So we're closing the distance between ourselves faster then light, but we're not.

Oh no, here comes the headache.

You're in your F15 at 200 m/s, a MiG-29 arrives at 200 m/s, you cross each other at 400 m/s but hear no sonicboom, because the sounds can "escape" the MiG to come through the window. It is you coming to the sound.

*thanks Lock On for your scenarios *

[Stochasty]

You're in your F15 at 200 m/s, a MiG-29 arrives at 200 m/s, you cross each other at 400 m/s but hear no sonicboom, because the sounds can "escape" the MiG to come through the window. It is you coming to the sound.

*thanks Lock On for your scenarios *

I understand the point of this argument, but unfortunately it's a faulty and counter-productive analogy; it teaches exactly the wrong lesson.

Sound travels through a medium (air), so when you talk about the speed of sound it is with respect to the reference frame of the medium through which it travels. This is why there is no sonic boom in your example. If the air happened to be moving in concert with one of the two planes, there would be a sonic boom.

This does not apply to relativity; light propagates without need for a medium. In your example, the closing speed of the craft is still 400m/s, exceeding the speed of sound despite the lack of a sonic boom. In the LHC example, two particles moving at .95c in the lab frame and colliding head on are emphatically not moving at 1.9c with respect to each other (their relative speed is ~.9987c). There is no "optic boom" in this case because the closing velocity does not (and cannot) exceed the speed of light from the perspective of either of the two particles.

This faulty analogy is illustrative of a lot of the problems that people have with relativity and the "headaches" it causes. It's because they persist in wanting to hold onto this Euclidean view of the world, which tells them that "adding velocities" is okay even when they know that the math says otherwise. It's just not true, and the only way to get over those headaches is to let go of your preconceived notions of how the worlds works. In relativity, everything is observer dependent (that's why it's called relativity); different observers travelling at different velocities see different things. You must internalize this concept first before things begin to make sense. Personally, I think the math is almost unimportant when it comes to conceptualizing things; it teaches people to pull out a calculator when they don't understand things rather than internalizing the concepts and developing a valid intuition for the subject.

Edited August 24, 2013 by Stochasty

[NGTOne]

I understand the point of this argument, but unfortunately it's a faulty and counter-productive analogy; it teaches exactly the wrong lesson.

Sound travels through a medium (air), so when you talk about the speed of sound it is with respect to the reference frame of the medium through which it travels. This is why there is no sonic boom in your example.

This does not apply to relativity; there is no medium for sound to travel. In your example, the closing speed of the craft is still 400m/s, exceeding the speed of sound despite the lack of a sonic boom. In the LHC example, two particles moving at .95c in the lab frame and colliding head on are emphatically not moving at 1.9c with respect to each other (their relative speed is ~.9987c). There is no "optic boom" in this case because the closing velocity does not (and cannot) exceed the speed of light from the perspective of either of the two particles.

This faulty analogy is illustrative of a lot of the problems that people have with relativity and the "headaches" it causes. It's because they persist in wanting to hold onto this Euclidean view of the world, which tells them that "adding velocities" is okay even when they know that the math says otherwise. It's just not true, and the only way to get over those headaches is to let go of your preconceived notions of how the worlds works. In relativity, everything is observer dependent (that's why it's called relativity); different observers travelling at different velocities see different things. You must internalize this concept first before things begin to make sense. Personally, I think the math is almost unimportant when it comes to conceptualizing things; it teaches people to pull out a calculator when they don't understand things rather than internalizing the concepts and developing a valid intuition for the subject.

I think the ultimate issue is that relativity is so UN-intuitive when compared to the world we perceive. Double that for when you throw in fun stuff like spacetime warping.

The world we perceive (unaided, naturally) conforms perfectly to Euclidean rules. If I'm on a train going north at 30 m/s and you're on a train going south at 30 m/s, we're gonna kill each other at a relative velocity of 60 m/s, and all observers, from the vantage points of both trains and someone standing next to the tracks, will agree on this. Without an education in physics (which most people lack), there is no simple way to develop an intuition for relativistic physics - it's too far outside what we intuitively understand from our perceptions of the world.

[Diche Bach]

Isn't it also true that, relativistic effects are relatively 'trivial' at lower velocities/time-space whatever thingamajig?

As far as the objects colliding, I don't get what you guys are getting at there, but lets take one I do get: time dilation as a result of different velocity of two entities. I was under the impression that some of the earliest 'proof' of relativity was derived from comparisons between atomic clocks that were left behind at the airport and one inside of a very fast aircraft. Over a sufficiently long journey and at high enough speeds, very tiny disparities (thousands of seconds?) accumulated showing that time had actually slowed down every so slightly for the aircraft.

In the "real world" in which human perception evolved, variance that small is irrelevant so it is perhaps not surprising if we are not very good at understanding it, and it is hard to demonstrate.

And by the way, what is the "LHC?" Is that some distinctive phase of the very early universe? Or is it the something Hadron Collider?

[K^2]

AIUI forwards is definitely on the cards, backwards is more iffy.

Backwards is only iffy from perspective of practicality. In terms of what it means to paradoxes, it's pretty straight forward. General relativity is nice and self-consistent if we allow exotic matter. With exotic matter we can most certainly allow for time travel. (Though, I do recall some solutions without it, I still need to look it up.) In either case, if GR allows for time travel into the past, even if it cannot be practically achieved whether it is due to very high energy requirements, unavailability of exotic matter, or any other hick-up, the very fact that GR allows for it in principle must mean that any theory that works with GR must allow for paradox resolution.

And in fact, within the framework of quantum field theory in curved space-time, where you can have closed time-loops, any and all time traveling paradoxes are resolved. The simplest explanations are from Many Worlds Interpretation, but it works in any interpretation you like.

There is one big exception, which is paradoxes which involve construction of the time machine. And unfortunately, these require space-time curvature itself to be a function of quantum fields, and that, in turn, requires quantum gravity to describe properly. So that part is iffy. But since the time machine can be constructed entirely outside of realms of quantum gravity, at least in theory, quantum gravity itself must allow for self-consistent time travel. And therefore, it must look after paradoxes involving time machine in some fashion. I suspect that the results will be identical as the quantum field theory resolution, but that's already speculative.

The short version is that we already know enough to say that any self-consistent theory must look after time travel, even if time travel is not actually possible in practical terms.

[Stochasty]

Without an education in physics (which most people lack), there is no simple way to develop an intuition for relativistic physics - it's too far outside what we intuitively understand from our perceptions of the world.

That's fine. I don't ask that non-physicists develop an intuition regarding the relativistic world; it's a hard subject. What I do ask is that the lay public realize and acknowledge the fact that they don't possess such an intuition, cannot possess one without investing significant effort into studying the subject, and therefore should not trust that what they naively expect to be true is in fact true: basically, what I'm trying to convey here is the depth of ignorance involved.

In my experience, most people tend to believe that the reason that physics is hard is because of the math, but believe that they've got a pretty good handle on things otherwise - in other words, they believe that the only thing hard about physics is the math. My point here is that that really isn't true; special relativity being a particularly good example thereof: it's a case where the math tends to obfuscate more than illuminate - it's not the math that makes things hard, it's the need to internalize an entirely new conceptual framework. Quantum physics is similar in this regard (probably the reason why these two disciplines are the most cited as headache inducers).

I'm not trying to be an asshole here by pointing this out: rather, this issue points to one of the big problems when it comes to scientific communication. There's a huge disconnect between a physicists conceptual understanding of the world and the lay public's conceptual understanding, and this disconnect tends to get glossed over. Physicists, when trying to explain things to the world at large, are forced to resort to vast oversimplifications, and a large part of the reason why is the lack of a common conceptual framework. I can try to be exact, and tell you that changes in velocity in relativity are just rotations of a unit vector in a hyperbolic 4-dimensional vector space, but it doesn't do anyone any good. I can resort to awkward concepts like time dilation and length contraction, but that means that not only do I have to try to explain these concepts to you, I also have to be able to explain away all of the apparent paradoxes that result from incomplete understanding of these concepts. I can go further, and resort to vague analogies, but at some point what I'm saying stops being the truth and becomes a convenient lie; a lie, because it's really not possible to describe relativity within the conceptual framework of everyday life.

Unfortunately, these oversimplifications tend to get overlooked when lay people discuss the issues amongst themselves. This is important, because the lay public's perception of science matters a whole lot more to the endeavor of scientific progress than does the opinions of the actual scientists themselves; it is the lay public who elects the politicians who control public policy and funding for research. So, it's important to do all we can to try to narrow the disconnect between lay public and scientist, and the first step to that is identifying the depth of the ignorance involved.

Edited August 24, 2013 by Stochasty

[NGTOne]

That's fine. I don't ask that non-physicists develop an intuition regarding the relativistic world; it's a hard subject. What I do ask is that the lay public realize and acknowledge the fact that they don't possess such an intuition, cannot possess one without investing significant effort into studying the subject, and therefore should not trust that what they naively expect to be true is in fact true: basically, what I'm trying to convey here is the depth of ignorance involved.

In my experience, most people tend to believe that the reason that physics is hard is because of the math, but believe that they've got a pretty good handle on things otherwise - in other words, they believe that the only thing hard about physics is the math. My point here is that that really isn't true; special relativity being a particularly good example thereof: it's a case where the math tends to obfuscate more than illuminate - it's not the math that makes things hard, it's the need to internalize an entirely new conceptual framework. Quantum physics is similar in this regard (probably the reason why these two disciplines are the most cited as headache inducers).

I'm not trying to be an asshole here by pointing this out: rather, this issue points to one of the big problems when it comes to scientific communication. There's a huge disconnect between a physicists conceptual understanding of the world and the lay public's conceptual understanding, and this disconnect tends to get glossed over. Physicists, when trying to explain things to the world at large, are forced to resort to vast oversimplifications, and a large part of the reason why is the lack of a common conceptual framework. I can try to be exact, and tell you that changes in velocity in relativity are just rotations of a unit vector in a hyperbolic 4-dimensional vector space, but it doesn't do anyone any good. I can resort to awkward concepts like time dilation and length contraction, but that means that not only do I have to try to explain these concepts to you, I also have to be able to explain away all of the apparent paradoxes that result from incomplete understanding of these concepts. I can go further, and resort to vague analogies, but at some point what I'm saying stops being the truth and becomes a convenient lie; a lie, because it's really not possible to describe relativity within the conceptual framework of everyday life.

Unfortunately, these oversimplifications tend to get overlooked when lay people discuss the issues amongst themselves. This is important, because the lay public's perception of science matters a whole lot more to the endeavor of scientific progress than does the opinions of the actual scientists themselves; it is the lay public who elects the politicians who control public policy and funding for research. So, it's important to do all we can to try to narrow the disconnect between lay public and scientist, and the first step to that is identifying the depth of the ignorance involved.

I agree completely - in principle. In practice, what you've suggested is rather close to impossible, for a few different reasons:

1. People don't (usually) like being told they don't know things. Those that do realize they don't know stuff tend to end up in places like this (or in Wikipedia freefall, but that's a whole other story).

2. Changing the public opinion of science and scientists is difficult - a lot of people view things such as theoretical physics as being "ivory tower", with no practical applications in the real world, especially not within their own lifetimes.

3. It's much easier (and sells much better) for the media to be alarmist and trumpet "The LHC will create a black hole and kill us all when it's switched on!", rather than "The LHC has a 1 in 10 quadrillion (or whatever that number is, I can't remember) chance of creating a tiny singularity that would blink out of existence as fast as it appeared". Generally speaking, people like news and information in bite-size pieces, and a detailed breakdown of the risks of the LHC, even without the technobabble, would bore them into changing the channel (bad for ad revenue).

Due to the rules of this forum, I'm not even going to touch on willful ignorance due to personal beliefs, but that's a factor as well.

In my personal view, to do what you've suggested and underline the depths of the public ignorance require the following:

1. Regard the current adult generation as a lost cause. Barring a minority, few have the cojones to admit that they don't know something, and that there might be more to this "physics" thing.

2. Implement sweeping changes to the education system - rather than a rigid system based on facts and tests, free-form, open-ended learning (within certain guidelines, naturally, to stay on topic) should be more encouraged, especially at a young age when curiosity and inqusitiveness are at their highest and the brain is at its most malleable (though this is a paradigm that should continue throughout elementary and high school - for instance, in high school, as opposed to a final exam, have students write a proper academic research paper on a topic of their choice [within the confines of the class curriculum]). Current systems are geared to produce children who hate learning, because learning feels like work - this is a paradigm that has to be reversed (it originates with a government desire to quantify educational progress - "Math scores increased by 5% since we started this new program", etc.).

[Person012345]

And by the way, what is the "LHC?" Is that some distinctive phase of the very early universe? Or is it the something Hadron Collider?

Large Hadron Collider.

[Person012345]

I understand the point of this argument, but unfortunately it's a faulty and counter-productive analogy; it teaches exactly the wrong lesson.

Sound travels through a medium (air), so when you talk about the speed of sound it is with respect to the reference frame of the medium through which it travels. This is why there is no sonic boom in your example. If the air happened to be moving in concert with one of the two planes, there would be a sonic boom.

This does not apply to relativity; light propagates without need for a medium. In your example, the closing speed of the craft is still 400m/s, exceeding the speed of sound despite the lack of a sonic boom. In the LHC example, two particles moving at .95c in the lab frame and colliding head on are emphatically not moving at 1.9c with respect to each other (their relative speed is ~.9987c). There is no "optic boom" in this case because the closing velocity does not (and cannot) exceed the speed of light from the perspective of either of the two particles.

This faulty analogy is illustrative of a lot of the problems that people have with relativity and the "headaches" it causes. It's because they persist in wanting to hold onto this Euclidean view of the world, which tells them that "adding velocities" is okay even when they know that the math says otherwise. It's just not true, and the only way to get over those headaches is to let go of your preconceived notions of how the worlds works. In relativity, everything is observer dependent (that's why it's called relativity); different observers travelling at different velocities see different things. You must internalize this concept first before things begin to make sense. Personally, I think the math is almost unimportant when it comes to conceptualizing things; it teaches people to pull out a calculator when they don't understand things rather than internalizing the concepts and developing a valid intuition for the subject.

Is my intuition right in assuming that the discrepency between what an outside neutral observer sees and what the particle sees can be explained by time dilation? If so that seems (to me) to be an infinitely less complicated answer than the contrived and flawed plane analogy anyway. As long as you can just accept that time dilates (as has been observationally proven) and that why that happens is a whole other discussion.

[K^2]

Is my intuition right in assuming that the discrepency between what an outside neutral observer sees and what the particle sees can be explained by time dilation?

Kind of depends on what you mean by a "neutral" observer. Basically, any observer's perspective is just as valid as any others. So there is no preferred observer, and therefore, there isn't anybody who's any more "neutral" than anyone else in any sense of the word that I'm familiar with.

There is a somewhat special class of observer frames known as inertial frames. If you want to think of these as more "neutral," that's fine. But so long as you keep acceleration in mind, perspective of an accelerated observer is also entirely valid.

But other than that, yes. Time dilation and space contraction are going to compensate for any disagreement between different observers. Unfortunately, it's not a terribly useful way to think about it if you want to actually predict what will happen. But if you just need a peace of mind, that works.

[Person012345]

Kind of depends on what you mean by a "neutral" observer. Basically, any observer's perspective is just as valid as any others. So there is no preferred observer, and therefore, there isn't anybody who's any more "neutral" than anyone else in any sense of the word that I'm familiar with.

There is a somewhat special class of observer frames known as inertial frames. If you want to think of these as more "neutral," that's fine. But so long as you keep acceleration in mind, perspective of an accelerated observer is also entirely valid.

Yeah, I know . I just mean your observers frame. In this case, one that is stationary with respect to the LHC apparatus or whatever I guess. Rather than being "on" either of the protons.

But other than that, yes. Time dilation and space contraction are going to compensate for any disagreement between different observers. Unfortunately, it's not a terribly useful way to think about it if you want to actually predict what will happen. But if you just need a peace of mind, that works.

Indeed, I'm commenting on how the contrived airplane analogy, even if it were accurate in some way (which as you said it isn't) actually seems more confusing (to me) than simply saying that time has slowed down for the protons. And whatever other effects are involved. Without going into huge detail. If we, as laymen trying to understand how two protons are closing both ftl and not ftl (depending on which frame your observing the event from), then that seems simpler than trying to explain through a sonic boom idea which, apart from being a bad analogy, I didn't even understand what it was trying to get at anyway. As long as we can just accept that time dilation (and other relativistic effects) exists (because it does) then it's really not all that difficult to understand why a proton only sees the other proton coming towards it at 0.9c rather than 1.9c in an intuitive way.

Of course if you want to go around predicting what will happen, you may need some degrees and a deeper understanding than the layman's anyway.