Aye, but where's the supernova remnant itself? The rapidly-rotating neutron star with the nasty high-energy pulsar radiation? It was at the center of the explosion, so it had an initial kinetic energy of nearly zero. It should still be in the stellar neighborhood.
It's becoming more common now to see pulsars and neutron stars with really high peculiar velocities away from the site of the explosion. Inhomogeneous conditions during the collapse and explosion can propel the remnant away from the center of the nebula. It's pretty likely that any compact remnant is now long gone after almost 5 billion years. Also, depending on the density of the surrounding cloud, the duration of the high-intensity pulsar phase is probably not nearly that long. Either the surrounding material is pushed away and dispersed way before that, or the pulsar spins up to the point of becoming a possible gamma-ray burst source and destroys itself.
Intersting stuff.. but when you consider time scales like this what kind of practical applications does this have?
Um, none? I suppose I could try to think of some technological offshoot of current astrophysical science, but to be safe let's just round down to 0. Is this "practicality" the metric by which you think we ought to measure all scientific findings?
Can anyone explain what knowledge is gained from these pretty pictures?
Ah, now this is easier. Watching a close interaction between galaxies helps understand collisions we see happening further away, and tightens constraints on cosmological and galactic evolution models (the latter is what I worked on). Of course the pretty pictures are shown to the public --- we're far more interested in the high-resolution spectra of these regions. Starburst regions are of intense interest because of the degree to which the nebulae are enriched promptly with elements like sulfer, silicon, and oxygen (from high-mass, short-lived stars). Then when we see these bright regions in more distant galaxies with a certain ratio of elemental abundances we can make a guess as to the age of the region and perhaps the embedding galaxy. The spectra of many regions also gives us dynamic information about the system's interaction, yielding a good estimate of the total mass interacting gravitationally. We can use these more precise measurements to constrain galactic dark matter models and distributions. And I'm sure there are a hundred other areas of specialized research that will be influenced by high-resolution data of galactic collisions.
Well, as long as you're allied with the present US administration. The newest space policy statement just released would "deny this freedom to our adversaries", speaking of the freedom of space exploration.
Man, that's the first time this phrase has *ever* been used to reference something that Inhofe has said. Usually we (Oklahomans) have to apologize for him when in learned company. And trying to imagine him "focusing on the science" is a strangely comical mental exercise.
This issue is being played so much by the media it is hard to get honest science.
Please. So the media is somehow controlling the puppet strings of the reviewers, authors, and reviewers of Nature, Science, and hundreds of other professional journals? The "honest science" is there for the reviewing if you're interested. If you're skeptical of the popular presentation of the results, you're free to not listen to it and go to the original sources.
So what you are saying is that if we have a bunch of measurements that have a varying uncertainties of say +/- 2 to +/-.7 that we can get a more accurate number but averaging them?
Right --- by including lots of measurements, the likelihood that the overall error is as large as any individual (or small ensemble) error is very small. Another poster brought up a good example. If you take a "random" sample of adult weights, you may find an average to be, say, 180 lbs, with an error (let's say this is represented by the standard deviation) of maybe 30 pounds, so you'd expect about 2/3 of people to be within 150-210 pounds, and 1/3 outside of this. If you then add together lots of these sample groups to get a national average, you'd find the standard deviation narrowing down much closer to the average. You might characterize a person's weight in the small group as being 180 +- 30, but in a national average the deviation is much smaller.
I would trust them if I did not find so many issues with the data I have been looking at. Just because they are smart and have spent there lives studying this, does not mean that they are right.
I agree, but historically those scientific theories that are upheld by a large consensus of specialists are generally not overturned by non-specialists from the outside. It is much more likely that the outsiders and non-specialists have made a crucial, though possibly subtle, error in analysis.
The most common omission I find is the error level on charts. Take the ice core samples, what is the error level? Most I have seen have stated that the current PPM of CO2 is at an all time high! It has been stated that the current CO2 levels are 330+ ppm and from ice cores we know it has never been higher, or do we? What is the error level of the ice cores? +/- ??? If it is +/- 500ppm than the charts are junk, if it is +/- 2ppm then they may mean something. To date I have not been able to find anything that states the accuracy of the reading or the error level of the ice cores.
This is part of basic, peer-reviewed science. I'd give them the benefit of the doubt and figure they've thought of that already. If they report the number as 330, it's reasonable to guess that it's around 330 +- 10. If you really can't find the uncertainties in the professional articles, email the authors. No offense, but I'd be shocked if you've thought of something they haven't.
The general consensus is that the global temp is up 0.5c +/-.2c. So the warming trend may be as high as.7c and as low as.3c. I can see this, but add to this that the temperature measurements have a posted error correction of +/-.7c we now have a problem. The global warming that may be happening is within the error rate of the temperature measurement. If Microsoft tried to use numbers like this we would tare them apart but the global warming crowd uses them and they are ok?
This is fine, as long as there are lots of measurements. Uncertainties add in quadrature, so we pin down a more narrow confidence level with a great number of measurements.
To those how would point to the chart that shows us warming, they all seem to start around 1880. This is odd as this marks the end of the little ice age, to say that we are warmer now than we were during the little ice age is, well, duh!
The point isn't just that we're warmer now than we've been since the 1880's, but the CO2 levels are the highest they've been in the last 800,000 years, at least. And we've broken through the 200-300 ppm envelope the levels have been in only the last 100 years, so it's the *rate* of increase that is particularly worrisome.
I am sorry, the science seems off and with out solid science to back it up I just can not believe the hype.
Again, and I don't mean any offense, but these seem like simplistic arguments. We might want to be humble enough to assume that these people, most of whom are really smart, and spend their whole professional lives studying just this phenomena, have already considered these things. I'm not advocating a blind appeal to authority, but it's only curteous to assume that the experts in the field carry *some* authoritative weight.
You continue to trot out the same inaccurate language and examples, and I've refuted every point. And, for what is now the last time, I'll reiterate that by invoking the word "accelerates", you've lost all rights to compare results derived using SR. Along the way somewhere, you have been hoodwinked by people claiming much more knowledge than they truly possess. Please stop listening and linking to crackpots, and open a good text on the subject and start studying for yourself.
Ok, I've had it. You've been belittling and belligerent, and acted like a complete ass. You've clearly had no intermediate or advanced schooling in physics, and yet you make brazen assertions that any halfway-specialist in the field would see as amateurish and misguided. I've spent too much time away from my students and research responding to an unreasonable buffoon, so I'm signing off. When you wish to be civil, feel free to email me and we can discuss physics some more.
BUT RELATIVITY DOES NOT ACCOUNT FOR THIS IN ANY EQUATION!
Of course not. It doesn't apply in that case. The Second Law of Thermodynamics does not account for the motion of an electron in a magnetic field, but we shouldn't infer that there's anything wrong with the thermodynamics because of this. There are regimes where we should use results from SR, and regimes where we shouldn't.
That is why it is fully possible to model the planet moving and the ship sitting still
Nope. It's completely different physics. The force required to accelerate the planet is very different from the force required to accelerate the ship. You're free to model the situation, but you're not free to say that it's the functional equivalent of the system where the ship is the one accelerating, and you're not free to use SR to compare results. Again, you can't use SR in a non-inertial frame. You just can't. If you want to make a big deal about the fact that SR is "broken" for non-inertial frames, it's hardly news, since it's only *defined* to be valid for inertial ones. That is, in fact, the *only* postulate you need to derive SR (the constancy of the speed of light is sort of a consequence of the postulate that all laws of physics give identical results in inertial frames).
Also, this does not address the cases in which both observers are moving equally.
I don't understand this. By "equally", do you mean that they're moving at a constant velocity with respect to each other? If so, there is no contradiction as I pointed out somewhere above.
Let me clarify - give the formulae in which the force behind the acceleration is taken into account. Acceleration, just like velocity, is symmetrical. From the perspective of the ship, the planet accelerates away from it.
No. This is what I'm saying --- it's *not* symmetrical. Only the ship is in an accelerating, non-inertial frame. Giving an observer in each frame the little box with a ball in the center, only the one on board the ship will move in response to its acceleration. Both observers will agree on this. Here's another example: say I hold a pendulum bob at the end of a string, and you hold one while driving away from me in a car. As long as you're traveling at a constant velocity away from me, both bobs hang vertically, and the frames are indistinguishable. As soon as you hit the brakes, accelerate, or round a curve, the bob will deflect from the vertical position. Only your bob does this. You can't say that, from your point of view, your bob stays vertical and you see mine deflecting. As soon as one frame becomes non-inertial, all bets are off and we can't use SR any more. I can't give you a "formula" that will get you what you want, because SR doesn't apply. You can look up the formulae for relativistic forces and accelerations as they would appear to observers in other frames, they're pretty easy to derive and appear in all elementary texts, but that's not what we're talking about here.
You've completely missed the point of the thought experiment. It assumes Newtonian physics, along with the premise that light travels at the same speed regardless of inertial frames. Thus it demonstrates the need for length and time dilation.
No, I get the point of the thought experiment, it's just a really poor and misleading demonstration that something like special relativity must be true. Glancing at any elementary-level text will reveal many better thought experiments that utilize the correct concept of proper time.
The follow-up experiment then assumes l/t dilation, but still fails to resolve the contradiction; ie. that each ship experiences less time than the other. If you'd like to see a clearer example of relativity's failure to resolve certain paradoxes (particularly those in which l/t dilation is symmetrical), see the link in my other post. (Oh, and by the way, special relativity ALWAYS applies to ALL inertial frames.
That each ship experiences less time than the other is *not* a contradiction. It only appears to be when we devise a way for them to return to each other to compare measurements, where the symmetry of the problem is broken --- one of the ships must *accelerate* to return to the other, and therefore special relativity no longer applies. As I indicated, I visited the link you supplied, and the arguments there suffer from this precise fallacy. You make the parenthetical remark as if that's something I'd argue with, when that's exactly the point I'm making. SR applies to all inertial frames, and *doesn't apply to non-inertial ones*.
To try to explain it again, consider the twins experiment - it can also be modelled with the twin on the ship staying still, and the planet flying away and returning. Thus it would be the twin on the planet that experiences less time. Acceleration is the apparent difference between the two, but that is NOT currently accounted for in relativity.
Of course it isn't accounted for. SR is not relevant in this domain. Your premise is false --- it *can't* be equivalently modeled by a stationary ship and a moving planet, because it's the ship that undergoes the accelerations. In other words, it's easy to distinguish between the frames: in both frames, keep a little box with a ball in the center. The ball will stay in the middle of the "stationary" box on the earth, but will roll around the ship's box since it has to accelerate and decelerate a couple of times. This will be true no matter which frame we're in, so we can easily distinguish which frame is accelerating. There is no way to set them up as equivalent (or relative) frames.
The fact that SR does not apply for non-inertial frames is indeed widely (universally) known. To say that this limitation implies that SR is "broken" or "wrong" is like saying that the spring force F=-kx is wrong because it doesn't work for objects sliding down inclined planes. It simply doesn't apply there.
I never said there was a conspiracy. It is simply that nobody with enough significance in the physics community is making a big deal out of this. And no, it won't shake the Earth if they do. First, it wouldn't surprise anyone who really knows the field, and second, no one has an answer yet.
You certainly insinuated that, even if someone knows something damning about SR, they wouldn't dare step forward. No one is making a big deal out of this because it's obvious to anyone who has successfully taken a course in SR. It's covered in the first couple days of a SR unit.
If you're going to trivialize all values of distance to the point that they are meaningless, then you're a fool.
Ok, I'll try again --- we can basically agree on local values of distance because, for a receding car on the freeway, the light travel time between the car and us is much shorter than the increase in the distance of the car during this light travel time. On larger scales, where the increase in separation due to the expansion of the universe is still significantly less than light speed, it's not too imprecise to measure distances to galaxies on the order of a hundred megaparsecs or so. At a redshift of, say, 10, the universe (and the galaxy, accordingly) was a factor of 10 (really 11, since it's z+1) closer to us at the time the light we observe now was emitted. To say that the light has crossed 13 billion light years of distance in the meantime is not right --- it is this distance itself that has increased in the meantime due to cosmological expansion, regardless of the particular model of how quickly the expansion occurred. This is related to the fundamental misunderstanding of special relativity that keeps popping up. To measure a *distance*, one needs *simultaneous* measurements of the boundaries in the rest frame of the observer. Here, with one end of the boundary possibly increasing its distance from us at speeds greater than that of light (it's certainly possible, in GR, for the coordinate distance of two galaxies to far exceed the speed of light in the expansion), assuming such a simultaneous measurement is meaningless. Sure, we all agree that light travels at speed c always, but it's the distance to be covered that keeps stretching during the transit.
And you claim to be a teacher of relativity? Ok, I'll assume for the moment that somehow that's true and yet you've never seen this basic thought experiment. I didn't intend to explain it, because it really needs a visual presentation, but here's the short version: both the planet and the ship count the number of blinks they see during the ships journey. The planet sees the last blink at the same time the ship gets there; the ship sees it earlier. Thus, it presents a contradiction in Newtonian physics, which can be resolved through length and time dilation.
We usually just say they carry identical, synchronized clocks. The distant blinking light makes the situation much more complicated because it doesn't measure the proper (local) time aboard the spaceship --- we need a clock *at rest in the frame of the ship*. I'm not sure how you're trying to interpret the results as being time dilation when you're not comparing the proper time in both frames. Using synchronized clocks, the seeming contradiction is not that the ship sees the light earlier, but that it will (if comparing proper clocks) count *fewer* blinks. Your example actually shows the opposite, that the ship will count *more* blinks in a shorter time.
Actually, if you want to get specific, there's a significant flaw in relativity in every thought experiment - from an outside perspective, there is no difference between the planet sitting in place with the ship moving, and the ship sitting in place with the planet moving. There is no explanation why it must be the ship that experiences less time - it's all a matter of perspective. The same can be said of the twins experiment or any other. That is what I modeled in the example I gave before - a perfectly symetrical system. Length and time dilation do not resolve this one, because they can't each experience less time than the other.
No! There is a huge difference between the frames in the twin experiment. One of the frames is no longer inertial (non-accelerating). This is also the running flaw in the link you provided. You simply can't compare a frame where special relativity applies with a frame where it doesn't. In inertial frames, length and time work together to resolve the seeming paradox. In the case of muon production and decay in the atmosphere, from a rest frame on the
I agree, but I didn't feel like taking on this assumption. I was simply stating that if something were indeed seen from 13 billion ly away, it would mean they were 13 billion ly away 13 billion years ago, when the light began travelling, as opposed to being 13 billion ly away right now. On the other hand, if the other galaxy is calculated to be 13 billion ly away now, it was much closer when the light we are now seeing had left it. I addressed the former possibility because it related to the parent post.
I understand, and forgive me for pressing a point that you may not care about, but neither of the possibilities you outline above are correct: The statements (a) "The galaxy was 13 billion light years away when the light was emitted" and (b) "The galaxy is now 13 billion light years away" are both not only wrong, but meaningless. The expansion of the universe renders all such distance and time estimates subject to a particular cosmological model in which they are evaluated; and it's only the redshift number, indicating the scale factor of the expansion, that carries any real meaning.
Here's the short version: It is well known that relativity is flawed.
I'd assert that it is far from well-known. Among physicists, to my knowledge, there is no known thought experiment or demonstration that cannot be reconciled with special relativity. The usual suspect in such "paradoxes" is to wrongly assume some simultaneous measurements in two frames in relative motion.
There's a common demonstration used to introduce people to relativity: a ship, a planet, and a light exist in space. The light blinks in a regular pattern. The ship starts next to the planet and flies to the light and back at a relativistic speed. In the process, we see that the ship has experienced less time than the planet. I'm not explaining this here; I assume you are familiar. If not, there are demonstrations available on the web.
Nope, not familiar with that one so much. What's the purpose of the blinking light?
So, once that is shown, take it one step farther. Four ships in a line; two have blinking lights on them. The two without lights start next to each other, the other two are the same distance from them (on opposite sides) that the light was from the planet in the previous example. Each of the outer ships flies inward, while the other two fly outward in opposite directions; for simplicity, make the speed of each be half the speed of the ship in the previous example. When the outer and inner ships meet, they turn around and return to their original positions. So now you can see that by removing either of the outer ships, you have a model equivalent to the first example. Thus, each of the middle ships experiences less time than the other! Nothing in relativity can account for this contradiction (yet).
Are you certain? I'm having trouble diagramming the setup, but I'd be glad to look at some kind of picture to make it more clear.
Relativity is wrong. We don't know the exact nature of what is wrong. Most of us, myself included, do not discount it altogether, but some do. Thus I say again, relativity is much less certain than many people believe.
These people must not be physicists, or at least this ground-shaking refutation of special relativity has not gotten the publicity your bald assertion would seem to warrant. I'd be glad to believe you, but as a teacher of relativity, color me skeptical.
Therefore, this galaxy would have had to have been 13 billion light years away from us at the time the light left it and began travelling towards us.
This isn't right. The "13 billion ly" is an unfortunately inaccurate, and probably meaningless number. It typically comes from plugging the value of the *redshift* of the galaxy (what is actually observed) into a particular cosmological model or, more commonly and naively, into simple Doppler redshift formulae. The distance of the galaxy at the time of emission was much closer than 13 billion ly away, since the size of the observable universe then was around a factor of 10 smaller than it is now --- this scale factor is what is given by the redshift. That's why we (astronomers) don't typically give distances of "billions" of light years. For objects at cosmological distances, there is no "now" (we're not in their light-cone yet), so no real meaning to "distance". We usually just report the redshift (z).
Of course, that's assuming relativity is correct, which is much less certain than many people believe.
I'm intrigued by your offer and would like to subscribe to your newsletter.
Nit-picking --- the mass equivalent of "pure" radiation *does* interact gravitationally with matter. That's why light bends around massive objects. A quantity of radiation will produce a gravitational field (actually, twice as much as the matter equivalent), it's just that the mass equivalent is pretty tiny.
What you're ignoring, and what is particularly alarming, is the *rate* of increase of the levels. There is some lag between the increase of CO2 and environmental effects, which is especially worrisome here because the rate has increased beyond recent bounds so quickly.
Re:Remember Vulcan? ( no, not startrek vulcan )
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No, I got the point, but I'll assert again that he seriously understates the evidence for DM, especially in the new work. It's a beautiful and compelling result, especially in the context of all the other evidence available.
This was the subject of an interesting paper by Tolman back in the 30's (37?) --- he derived the gravitational acceleration of a point mass due to a "pencil" of light passing by and showed that a field of radiation is a source of gravity just like the equivalent matter density would be, except for a bedeviling factor of 2. Kewl.
Re:Remember Vulcan? ( no, not startrek vulcan )
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It was PROVEN to exist in the late 1800s.
Obviously not. Perhaps the anomaly in Mercury's orbit was *suggestive* of another perturbing body.
And they saw it.
They did????
Vulcan had more data in favor of its existence back then than dark matter does now. Pardon me, but I'm as skeptical as parent.
You are mistaken (or just hyperbolic) as to the preponderance of evidence on both counts. And even stipulating that what you say *isn't* nonsense, they are completely unrelated, so the existence of dark matter does not logically depend on the existence of Vulcan.
This was an early objection to the paradox, but was later shown to be irrelevant since any gas blocking the light from distant stars would eventually heat up (by conservation of energy) to the average temperature of those distant stars and would glow itself.
Zeroth, stray neutrons decay to a proton, electron, and an electron anti-neutrino. n->p+n doesn't conserve charge.
First, "ordinary" baryonic matter like protons can only be (according to the well-verified Big Bang Nucleosynthesis) a few percent of the total mass density of the universe, and perhaps 10% of the total amount of Dark Matter. We think the dark stuff is largely, if not almost completely, non-baryonic (not made of quarks, not strongly interacting).
Next, for any isolated mass of protons (essentially ionized H), you'd have to explain where all the electrons went, since the Universe appears to be electrically neutral on even small scales. Also, since the electric force is so overwhelmingly much stronger than gravity, any such cloud cannot be gravitationally bound and would explosively disperse. It wouldn't be perfectly transparent, since protons (being charged) have some cross-section to scatter photons just like free electrons do. In fact, the X-ray emission mentioned in the article comes from hot, ionized H.
Re:Blog First, Then Scientific Journals.
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Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal or announced at a news conference...not on a blog shared by Mark, Claire, and Sean, whoever they may be.
They're physicists (I think Sean Carroll works in cosmology, formerly of the U. of Chicago, now at Cal Tech). It was announced, and the paper has been written. The blog, by the way, is really good.
who the hell leaves their 8 year old in a situation where they would need to call someone in an emergency but wouldn't have landline access?!
It's called a *mistake*
I'm 21
Ah, that explains it.
8 year olds should NEVER be put in a situation where they would need a cell phone.
Of course not. Mistakes happen. They can get easily separated in crowded areas (heck, even a Wal-Mart), and having a special-purpose phone would save parents like me a lot of panic. I would only give them the phone in these special circumstances.
The way I teach it in my classes is that there are 4 inner planets, 4 outer planets, and a (large) set of Kuiper Belt objects, of which Pluto is one of the largest and closest members. Why do we need a planetary definition? Historically, any serious attempt to classify natural objects eventually runs into problems anyway, especially when our first attempt includes objects that obviously belong to a number of sub-classes, each of which contains a continuum of members.
Slashdot Mirror
It's becoming more common now to see pulsars and neutron stars with really high peculiar velocities away from the site of the explosion. Inhomogeneous conditions during the collapse and explosion can propel the remnant away from the center of the nebula. It's pretty likely that any compact remnant is now long gone after almost 5 billion years. Also, depending on the density of the surrounding cloud, the duration of the high-intensity pulsar phase is probably not nearly that long. Either the surrounding material is pushed away and dispersed way before that, or the pulsar spins up to the point of becoming a possible gamma-ray burst source and destroys itself.
...so you went to Dock Preferences and unchecked the "Magnification" box, and they still jumped out at you?
Um, none? I suppose I could try to think of some technological offshoot of current astrophysical science, but to be safe let's just round down to 0. Is this "practicality" the metric by which you think we ought to measure all scientific findings?
Can anyone explain what knowledge is gained from these pretty pictures?
Ah, now this is easier. Watching a close interaction between galaxies helps understand collisions we see happening further away, and tightens constraints on cosmological and galactic evolution models (the latter is what I worked on). Of course the pretty pictures are shown to the public --- we're far more interested in the high-resolution spectra of these regions. Starburst regions are of intense interest because of the degree to which the nebulae are enriched promptly with elements like sulfer, silicon, and oxygen (from high-mass, short-lived stars). Then when we see these bright regions in more distant galaxies with a certain ratio of elemental abundances we can make a guess as to the age of the region and perhaps the embedding galaxy. The spectra of many regions also gives us dynamic information about the system's interaction, yielding a good estimate of the total mass interacting gravitationally. We can use these more precise measurements to constrain galactic dark matter models and distributions. And I'm sure there are a hundred other areas of specialized research that will be influenced by high-resolution data of galactic collisions.
Well, as long as you're allied with the present US administration. The newest space policy statement just released would "deny this freedom to our adversaries", speaking of the freedom of space exploration.
Man, that's the first time this phrase has *ever* been used to reference something that Inhofe has said. Usually we (Oklahomans) have to apologize for him when in learned company. And trying to imagine him "focusing on the science" is a strangely comical mental exercise.
This issue is being played so much by the media it is hard to get honest science.
Please. So the media is somehow controlling the puppet strings of the reviewers, authors, and reviewers of Nature, Science, and hundreds of other professional journals? The "honest science" is there for the reviewing if you're interested. If you're skeptical of the popular presentation of the results, you're free to not listen to it and go to the original sources.
Right --- by including lots of measurements, the likelihood that the overall error is as large as any individual (or small ensemble) error is very small. Another poster brought up a good example. If you take a "random" sample of adult weights, you may find an average to be, say, 180 lbs, with an error (let's say this is represented by the standard deviation) of maybe 30 pounds, so you'd expect about 2/3 of people to be within 150-210 pounds, and 1/3 outside of this. If you then add together lots of these sample groups to get a national average, you'd find the standard deviation narrowing down much closer to the average. You might characterize a person's weight in the small group as being 180 +- 30, but in a national average the deviation is much smaller.
I would trust them if I did not find so many issues with the data I have been looking at. Just because they are smart and have spent there lives studying this, does not mean that they are right.
I agree, but historically those scientific theories that are upheld by a large consensus of specialists are generally not overturned by non-specialists from the outside. It is much more likely that the outsiders and non-specialists have made a crucial, though possibly subtle, error in analysis.
This is part of basic, peer-reviewed science. I'd give them the benefit of the doubt and figure they've thought of that already. If they report the number as 330, it's reasonable to guess that it's around 330 +- 10. If you really can't find the uncertainties in the professional articles, email the authors. No offense, but I'd be shocked if you've thought of something they haven't.
The general consensus is that the global temp is up 0.5c +/- .2c. So the warming trend may be as high as .7c and as low as .3c. I can see this, but add to this that the temperature measurements have a posted error correction of +/- .7c we now have a problem. The global warming that may be happening is within the error rate of the temperature measurement. If Microsoft tried to use numbers like this we would tare them apart but the global warming crowd uses them and they are ok?
This is fine, as long as there are lots of measurements. Uncertainties add in quadrature, so we pin down a more narrow confidence level with a great number of measurements.
To those how would point to the chart that shows us warming, they all seem to start around 1880. This is odd as this marks the end of the little ice age, to say that we are warmer now than we were during the little ice age is, well, duh!
The point isn't just that we're warmer now than we've been since the 1880's, but the CO2 levels are the highest they've been in the last 800,000 years, at least. And we've broken through the 200-300 ppm envelope the levels have been in only the last 100 years, so it's the *rate* of increase that is particularly worrisome.
I am sorry, the science seems off and with out solid science to back it up I just can not believe the hype.
Again, and I don't mean any offense, but these seem like simplistic arguments. We might want to be humble enough to assume that these people, most of whom are really smart, and spend their whole professional lives studying just this phenomena, have already considered these things. I'm not advocating a blind appeal to authority, but it's only curteous to assume that the experts in the field carry *some* authoritative weight.
Ok, I've had it. You've been belittling and belligerent, and acted like a complete ass. You've clearly had no intermediate or advanced schooling in physics, and yet you make brazen assertions that any halfway-specialist in the field would see as amateurish and misguided. I've spent too much time away from my students and research responding to an unreasonable buffoon, so I'm signing off. When you wish to be civil, feel free to email me and we can discuss physics some more.
Of course not. It doesn't apply in that case. The Second Law of Thermodynamics does not account for the motion of an electron in a magnetic field, but we shouldn't infer that there's anything wrong with the thermodynamics because of this. There are regimes where we should use results from SR, and regimes where we shouldn't.
That is why it is fully possible to model the planet moving and the ship sitting still
Nope. It's completely different physics. The force required to accelerate the planet is very different from the force required to accelerate the ship. You're free to model the situation, but you're not free to say that it's the functional equivalent of the system where the ship is the one accelerating, and you're not free to use SR to compare results. Again, you can't use SR in a non-inertial frame. You just can't. If you want to make a big deal about the fact that SR is "broken" for non-inertial frames, it's hardly news, since it's only *defined* to be valid for inertial ones. That is, in fact, the *only* postulate you need to derive SR (the constancy of the speed of light is sort of a consequence of the postulate that all laws of physics give identical results in inertial frames).
Also, this does not address the cases in which both observers are moving equally.
I don't understand this. By "equally", do you mean that they're moving at a constant velocity with respect to each other? If so, there is no contradiction as I pointed out somewhere above.
No. This is what I'm saying --- it's *not* symmetrical. Only the ship is in an accelerating, non-inertial frame. Giving an observer in each frame the little box with a ball in the center, only the one on board the ship will move in response to its acceleration. Both observers will agree on this. Here's another example: say I hold a pendulum bob at the end of a string, and you hold one while driving away from me in a car. As long as you're traveling at a constant velocity away from me, both bobs hang vertically, and the frames are indistinguishable. As soon as you hit the brakes, accelerate, or round a curve, the bob will deflect from the vertical position. Only your bob does this. You can't say that, from your point of view, your bob stays vertical and you see mine deflecting. As soon as one frame becomes non-inertial, all bets are off and we can't use SR any more. I can't give you a "formula" that will get you what you want, because SR doesn't apply. You can look up the formulae for relativistic forces and accelerations as they would appear to observers in other frames, they're pretty easy to derive and appear in all elementary texts, but that's not what we're talking about here.
No, I get the point of the thought experiment, it's just a really poor and misleading demonstration that something like special relativity must be true. Glancing at any elementary-level text will reveal many better thought experiments that utilize the correct concept of proper time.
The follow-up experiment then assumes l/t dilation, but still fails to resolve the contradiction; ie. that each ship experiences less time than the other. If you'd like to see a clearer example of relativity's failure to resolve certain paradoxes (particularly those in which l/t dilation is symmetrical), see the link in my other post. (Oh, and by the way, special relativity ALWAYS applies to ALL inertial frames.
That each ship experiences less time than the other is *not* a contradiction. It only appears to be when we devise a way for them to return to each other to compare measurements, where the symmetry of the problem is broken --- one of the ships must *accelerate* to return to the other, and therefore special relativity no longer applies. As I indicated, I visited the link you supplied, and the arguments there suffer from this precise fallacy. You make the parenthetical remark as if that's something I'd argue with, when that's exactly the point I'm making. SR applies to all inertial frames, and *doesn't apply to non-inertial ones*.
To try to explain it again, consider the twins experiment - it can also be modelled with the twin on the ship staying still, and the planet flying away and returning. Thus it would be the twin on the planet that experiences less time. Acceleration is the apparent difference between the two, but that is NOT currently accounted for in relativity.
Of course it isn't accounted for. SR is not relevant in this domain. Your premise is false --- it *can't* be equivalently modeled by a stationary ship and a moving planet, because it's the ship that undergoes the accelerations. In other words, it's easy to distinguish between the frames: in both frames, keep a little box with a ball in the center. The ball will stay in the middle of the "stationary" box on the earth, but will roll around the ship's box since it has to accelerate and decelerate a couple of times. This will be true no matter which frame we're in, so we can easily distinguish which frame is accelerating. There is no way to set them up as equivalent (or relative) frames.
The fact that SR does not apply for non-inertial frames is indeed widely (universally) known. To say that this limitation implies that SR is "broken" or "wrong" is like saying that the spring force F=-kx is wrong because it doesn't work for objects sliding down inclined planes. It simply doesn't apply there.
I never said there was a conspiracy. It is simply that nobody with enough significance in the physics community is making a big deal out of this. And no, it won't shake the Earth if they do. First, it wouldn't surprise anyone who really knows the field, and second, no one has an answer yet.
You certainly insinuated that, even if someone knows something damning about SR, they wouldn't dare step forward. No one is making a big deal out of this because it's obvious to anyone who has successfully taken a course in SR. It's covered in the first couple days of a SR unit.
Ok, I'll try again --- we can basically agree on local values of distance because, for a receding car on the freeway, the light travel time between the car and us is much shorter than the increase in the distance of the car during this light travel time. On larger scales, where the increase in separation due to the expansion of the universe is still significantly less than light speed, it's not too imprecise to measure distances to galaxies on the order of a hundred megaparsecs or so. At a redshift of, say, 10, the universe (and the galaxy, accordingly) was a factor of 10 (really 11, since it's z+1) closer to us at the time the light we observe now was emitted. To say that the light has crossed 13 billion light years of distance in the meantime is not right --- it is this distance itself that has increased in the meantime due to cosmological expansion, regardless of the particular model of how quickly the expansion occurred. This is related to the fundamental misunderstanding of special relativity that keeps popping up. To measure a *distance*, one needs *simultaneous* measurements of the boundaries in the rest frame of the observer. Here, with one end of the boundary possibly increasing its distance from us at speeds greater than that of light (it's certainly possible, in GR, for the coordinate distance of two galaxies to far exceed the speed of light in the expansion), assuming such a simultaneous measurement is meaningless. Sure, we all agree that light travels at speed c always, but it's the distance to be covered that keeps stretching during the transit.
And you claim to be a teacher of relativity? Ok, I'll assume for the moment that somehow that's true and yet you've never seen this basic thought experiment. I didn't intend to explain it, because it really needs a visual presentation, but here's the short version: both the planet and the ship count the number of blinks they see during the ships journey. The planet sees the last blink at the same time the ship gets there; the ship sees it earlier. Thus, it presents a contradiction in Newtonian physics, which can be resolved through length and time dilation.
We usually just say they carry identical, synchronized clocks. The distant blinking light makes the situation much more complicated because it doesn't measure the proper (local) time aboard the spaceship --- we need a clock *at rest in the frame of the ship*. I'm not sure how you're trying to interpret the results as being time dilation when you're not comparing the proper time in both frames. Using synchronized clocks, the seeming contradiction is not that the ship sees the light earlier, but that it will (if comparing proper clocks) count *fewer* blinks. Your example actually shows the opposite, that the ship will count *more* blinks in a shorter time.
Actually, if you want to get specific, there's a significant flaw in relativity in every thought experiment - from an outside perspective, there is no difference between the planet sitting in place with the ship moving, and the ship sitting in place with the planet moving. There is no explanation why it must be the ship that experiences less time - it's all a matter of perspective. The same can be said of the twins experiment or any other. That is what I modeled in the example I gave before - a perfectly symetrical system. Length and time dilation do not resolve this one, because they can't each experience less time than the other.
No! There is a huge difference between the frames in the twin experiment. One of the frames is no longer inertial (non-accelerating). This is also the running flaw in the link you provided. You simply can't compare a frame where special relativity applies with a frame where it doesn't. In inertial frames, length and time work together to resolve the seeming paradox. In the case of muon production and decay in the atmosphere, from a rest frame on the
I understand, and forgive me for pressing a point that you may not care about, but neither of the possibilities you outline above are correct: The statements (a) "The galaxy was 13 billion light years away when the light was emitted" and (b) "The galaxy is now 13 billion light years away" are both not only wrong, but meaningless. The expansion of the universe renders all such distance and time estimates subject to a particular cosmological model in which they are evaluated; and it's only the redshift number, indicating the scale factor of the expansion, that carries any real meaning.
Here's the short version: It is well known that relativity is flawed.
I'd assert that it is far from well-known. Among physicists, to my knowledge, there is no known thought experiment or demonstration that cannot be reconciled with special relativity. The usual suspect in such "paradoxes" is to wrongly assume some simultaneous measurements in two frames in relative motion.
There's a common demonstration used to introduce people to relativity: a ship, a planet, and a light exist in space. The light blinks in a regular pattern. The ship starts next to the planet and flies to the light and back at a relativistic speed. In the process, we see that the ship has experienced less time than the planet. I'm not explaining this here; I assume you are familiar. If not, there are demonstrations available on the web.
Nope, not familiar with that one so much. What's the purpose of the blinking light?
So, once that is shown, take it one step farther. Four ships in a line; two have blinking lights on them. The two without lights start next to each other, the other two are the same distance from them (on opposite sides) that the light was from the planet in the previous example. Each of the outer ships flies inward, while the other two fly outward in opposite directions; for simplicity, make the speed of each be half the speed of the ship in the previous example. When the outer and inner ships meet, they turn around and return to their original positions. So now you can see that by removing either of the outer ships, you have a model equivalent to the first example. Thus, each of the middle ships experiences less time than the other! Nothing in relativity can account for this contradiction (yet).
Are you certain? I'm having trouble diagramming the setup, but I'd be glad to look at some kind of picture to make it more clear.
Relativity is wrong. We don't know the exact nature of what is wrong. Most of us, myself included, do not discount it altogether, but some do. Thus I say again, relativity is much less certain than many people believe.
These people must not be physicists, or at least this ground-shaking refutation of special relativity has not gotten the publicity your bald assertion would seem to warrant. I'd be glad to believe you, but as a teacher of relativity, color me skeptical.
This isn't right. The "13 billion ly" is an unfortunately inaccurate, and probably meaningless number. It typically comes from plugging the value of the *redshift* of the galaxy (what is actually observed) into a particular cosmological model or, more commonly and naively, into simple Doppler redshift formulae. The distance of the galaxy at the time of emission was much closer than 13 billion ly away, since the size of the observable universe then was around a factor of 10 smaller than it is now --- this scale factor is what is given by the redshift. That's why we (astronomers) don't typically give distances of "billions" of light years. For objects at cosmological distances, there is no "now" (we're not in their light-cone yet), so no real meaning to "distance". We usually just report the redshift (z).
Of course, that's assuming relativity is correct, which is much less certain than many people believe.
I'm intrigued by your offer and would like to subscribe to your newsletter.
Nit-picking --- the mass equivalent of "pure" radiation *does* interact gravitationally with matter. That's why light bends around massive objects. A quantity of radiation will produce a gravitational field (actually, twice as much as the matter equivalent), it's just that the mass equivalent is pretty tiny.
What you're ignoring, and what is particularly alarming, is the *rate* of increase of the levels. There is some lag between the increase of CO2 and environmental effects, which is especially worrisome here because the rate has increased beyond recent bounds so quickly.
No, I got the point, but I'll assert again that he seriously understates the evidence for DM, especially in the new work. It's a beautiful and compelling result, especially in the context of all the other evidence available.
This was the subject of an interesting paper by Tolman back in the 30's (37?) --- he derived the gravitational acceleration of a point mass due to a "pencil" of light passing by and showed that a field of radiation is a source of gravity just like the equivalent matter density would be, except for a bedeviling factor of 2. Kewl.
Obviously not. Perhaps the anomaly in Mercury's orbit was *suggestive* of another perturbing body.
And they saw it.
They did????
Vulcan had more data in favor of its existence back then than dark matter does now. Pardon me, but I'm as skeptical as parent.
You are mistaken (or just hyperbolic) as to the preponderance of evidence on both counts. And even stipulating that what you say *isn't* nonsense, they are completely unrelated, so the existence of dark matter does not logically depend on the existence of Vulcan.
This was an early objection to the paradox, but was later shown to be irrelevant since any gas blocking the light from distant stars would eventually heat up (by conservation of energy) to the average temperature of those distant stars and would glow itself.
Just picking nits, but "pure" energy has gravity also, which is why light interacts with massive bodies gravitationally and bends around them.
Zeroth, stray neutrons decay to a proton, electron, and an electron anti-neutrino. n->p+n doesn't conserve charge.
First, "ordinary" baryonic matter like protons can only be (according to the well-verified Big Bang Nucleosynthesis) a few percent of the total mass density of the universe, and perhaps 10% of the total amount of Dark Matter. We think the dark stuff is largely, if not almost completely, non-baryonic (not made of quarks, not strongly interacting).
Next, for any isolated mass of protons (essentially ionized H), you'd have to explain where all the electrons went, since the Universe appears to be electrically neutral on even small scales. Also, since the electric force is so overwhelmingly much stronger than gravity, any such cloud cannot be gravitationally bound and would explosively disperse. It wouldn't be perfectly transparent, since protons (being charged) have some cross-section to scatter photons just like free electrons do. In fact, the X-ray emission mentioned in the article comes from hot, ionized H.
They're physicists (I think Sean Carroll works in cosmology, formerly of the U. of Chicago, now at Cal Tech). It was announced, and the paper has been written. The blog, by the way, is really good.
It's called a *mistake*
I'm 21
Ah, that explains it.
8 year olds should NEVER be put in a situation where they would need a cell phone.
Of course not. Mistakes happen. They can get easily separated in crowded areas (heck, even a Wal-Mart), and having a special-purpose phone would save parents like me a lot of panic. I would only give them the phone in these special circumstances.
The way I teach it in my classes is that there are 4 inner planets, 4 outer planets, and a (large) set of Kuiper Belt objects, of which Pluto is one of the largest and closest members. Why do we need a planetary definition? Historically, any serious attempt to classify natural objects eventually runs into problems anyway, especially when our first attempt includes objects that obviously belong to a number of sub-classes, each of which contains a continuum of members.