Not true it would be possible to have a string theory without strings. That depends on what you mean by "string theory". All string "theories" are part of the same theory, so you can always dynamically evolve from a state without strings to one with strings. And any perturbative sector of string theory, with a classical limit, will have string excitations.
As far as somehow observing strings it is true we could directly observe empirical data which is implied by "stringy physics" but the concept of a string is a philosophical concept. The concept of anything is a "philosophical concept". You are a "philosophical concept". That doesn't prevent people from saying that you exist.
Not to say mathematics doesn't have a physical existence but rather what the word/concept "string" points towards is not a "physical" thing in the Cartesian sense. [...] What would be observed is empirical data that matches a mathematical formula where the variable for "string" is isolated. It's not like the concept of a rock where you can pick one up and actually confirm its existence. [...] However an electron is surely more "real" than a string. Strings exist in the same physical sense that electrons, atoms, or rocks do. Electrons are not "surely more `real' than a string"; they are described from mathematical formulas as well (just different ones). In fact, in string theory, electrons are strings, or rather vibrational modes of strings. A string is no more nor less "physical" than a rock, and being able to pick up a rock does not enable you to philosophically confirm its existence.
I believe that research in the field would have sped up if Einstein hadn't so been so public in his denouncing it.
As far as I can tell, Einstein's arguments did nothing to slow research in the field. Most people were on Bohr's side by that time.
Slowly Bohr managed to win and lets face it the EPR paper was an embarresment, then whoom as you said everyonewas on the qm band wagon.
The EPR paper wasn't an "embarrassment", it remains one of the most important papers on foundational QM, and the QM bandwagon started as soon as Heisenberg published his paper.
I remember that the current BB model had to be revisited to account for new theories in QCD/QED.
The main influence that quantum field theory has had on Big Bang cosmology is that the Higgs boson inspired the invention of inflationary cosmology. Far from modifying the BB picture, inflation solved a number of its long-standing problems.
QFT has also had influences in other areas of now-accepted cosmology, such as dark matter, but that doesn't affect the Big Bang much.
I tried to locate the article and found this one. It's interesting what he has to say, especially about the shift in ideas. I don't know much about the physics (nor, sadly the time to get into again) to say one way or the other. Maybe you've heard of it. If so what do you think? http://www.rense.com/general53/bbng.htm
Lerner is a pretty well known crackpot. (See Ned Wright's discussion here. He and Lerner had a back-and-forth and Wright eventually gave up arguing with him.) On the list of signatories are other people like the founders of Steady State cosmology, a theory which failed decades ago.
As for the scientific criticisms, yes Big Bang cosmology needs inflation and dark matter. One man's "fudge factor" is another's new theory. It's absurd to claim that BB cosmology has not made any predictions; it predicts an expanding universe, the existence and blackbody spectrum of the CMBR, light-element nucleosynthesis rate ratios, it accounts for measurements of luminosity-redshift curves, it predicts hotter temperatures in the past which have been observed, and so on. Inflation makes specific predictions about the statistical power distribution of the CMBR spectrum which have been confirmed. Dark matter has a wide range of evidence in its favor from galactic rotation to clusters to large-scale structure formation to cosmology. Furthermore, it is now known that candidate particles for the inflaton and dark matter appear naturally in almost every extension to the Standard Model that people have thought up — and not because they were added in explicitly to serve as inflatons or dark matter — including some in the Standard Model itself; inflation and dark matter could be predicted on the basis of particle physics alone.
During my four years at Uni I was told the models for neutron stars, planetary creation etc were constantly under debate to match observations with newer technology. Fair enough, I'm the first to say we can't know everything about a system and that we need to rethink when new data is found, but my point is if so many of our models are under doubt then why are our climate models so trustworthy?
Well, for one, they don't depend on unknown physics like the behavior of quantum chromodynamics at high densities. They also are based on far more data than we have about stellar interiors.
That being said, our current climate models aren't terribly accurate, by most physics standards. But climatologists have found that they get decent results when they average the predictions of an ensemble of climate models. In short, it's not the case that we can't use models accurately. Their predictions vary (I showed you graphs of that), but model calibration studies give reason to believe that the true values fall somewher
Well there was Newton and his optics. Something more 20th century would be nice.
The Einstein and his suggestion based on his model, that cold fusion was impossible. Einstein never said anything about cold fusion, and he didn't shut down research in the field.
And then the one that made it: QM fathered (ironically by Einstein) opposed to by everyone except a select few and look at it now... thankfully. QM was not "opposed by everyone". In fact, it was very obvious from the outset that it was an important advance, and in very short order everyone who was anyone was working on it; people just hated its philosophical implications.
I read recently that advents in QCD / QED have brought the Big Bang and the current mathematical models for Black Holes under doubt. I've not heard anything like that, and I came out of the gravitational physics field. But if you can point me towards a source, I can tell you what I think.
But with physics we knew the variables and the equations of state etc. Do our current enviromental models have that same level of detail? We know variables and equations of state in climate models. I'm not sure what you're getting at. Certainly we don't know everything perfectly, not even in physics. (See the research on the equations of state involved in quantum chromodynamics or neutron star interiors, or the problems with computer models of supernovae.)
Fair enough they can't handle the whole truth, but watered down versions, and at the very least the knowledge that what you see on the news isn't everything, is all they need. Also fair enough, but I'm still leery of talking to them about climate physics without having decent expertise in the field. I've seen too many garbled presentations of science at a lay level.
It's like I said before. An Legend dismisses an area of scientific research and all the others follow. Could you give an example of "a legend" (meaning, one person) dismissing an area of research and everyone else deciding to dismiss it as well because of what this one person said?
However now that Some Pillars of physics (Einstein's field equations, black holes, and the big bang) are being revisited and Scrutinised in the light of the overwhelming success of quantum mechanics, qed and qcd, I hope other areas will be opened up and investigated without bias. Those areas of physics always have been scrutinized. There was no groupthink suppressing investigation into alternatives. Actually, though, the evidence for black holes and the Big Bang is stronger than ever.
I can't remember exactly the details but the Antigrav this was a group in South America (Peru) I think who claimed they had built an antigrav device using magnets (some field device anyway). I've never heard of that, could you be thinking of the Podkletnov controversy?
From what I remember their theory was resonable and they had some (cooked) evidence. Some institution gave them some money and well that was the last anyone saw of them. Now Anti grave research has that stigma attatched to it. Antigravity devices don't have a stigma because of some particular research group faking data. They have a stigma because they nobody has ever produced credible evidence for antigravity nor a credible physical theory responsible for it.
I know what you mean, being an ex-theoretical physicist myself, but I should note that climatology really is primarily physics (plus chemistry, and some economics mixed in for emissions forecasts), even if it is usually done in department that doesn't have "physics" in its name. It's a bit more comparable to astronomy than traditional "physics", since they often have only sparse observational data with large error bars.
Honestly, it's very hard for students at that level to usefully evaluate the evidence in such a field; it would probably take a year of dedicated study to get a handle on the real issues. Sadly, it's hard to get away from "the experts said so" without further scientific background.
Well that's what this rumour I heard said. That this guy made up global warming, going against the then staus quo to secure a grant. James Hansen did not "make up" global warming. He got famous by testifying about it in Congress, but many scientists over many years have been publishing on the subject.
God knows we've had this in the world of physics: Antigravity devices, extreme low temp plasma - fusion. And all of these by then reputable scientists. I am not aware of any reputable scientists who have proposed antigravity devices. As for low-temperature fusion (I guess you are not talking about Pons-Fleischman cold fusion), what are you saying here? That this phenomenon was lied about in order to secure grant money?
ust out of interest what do you think the final outcome would be? Could the Earth stabalise or are "we all going to die":-) The worst case scenarios are if the Greenland ice sheet (GIS) melts or the West Antarctic ice sheet (WAIS) disintegrates. If either of those happens, we're in for tens of feet of sea level rise over perhaps decadal time scales, which would require major evacuation efforts from coastal cities. However, both of them are unlikely, with the latter more unlikely than the former. More likely we will see less effect — a few feet of sea level rise, more extreme and different patterns of weather, disruption of various agriculture and various ecological systems, things like that. Different regions will be hit worse than others, but we can't yet predict which regions will get which effects. That said, the "doom" scenarios are significant enough that they need to be taken into consideration; they are not so unlikely that they can be ignored, given their potential impact. They might not happen for centuries, but if they do happen, we have to think about it now, since it takes many decades to really change the course of the climate (given, e.g., the longevity of CO2 in the atmosphere).
You can find decent if sketchy summaries of some of these issues on the Wikipedia pages on global warming, GIS and WAIS, etc.
Especially as many of pupils are asking and I want to give them solid answers based on fact and scientific accuracy, not just unsupported claims by a media that we know not only lies to us, but instils fears. I should mention that you will probably find this hard to do. It will take you a while to just learn what the facts and accepted theories are, and much longer to understand why they are believed. Answers that you can't back up might be worse for your students than no answers at all.
By the way, what subject do you teach, and at what level?
You will note that the global warming on Pluto is attributed to it recently having been at its closest approach to the Sun, which has nothing to do with global warming on Earth. (But maybe you were just joking, I'm not sure.)
I know (first hand) what research scientists will do for grant money, but you're right it would be a little hard to conceive of it on this scale.
You can get grant money for results which challenge the status quo. In fact, you can get a lot of grant money this way, as long as you can back up your claims. On a more mundane level, you can certainly get grant money for work that reevaluates the reliability of climate models, temperature reconstructions, etc.
It has happened in the past with Newton's theories of light, for over a hundred years the Royal Society refused to accept anything that went against Newtonian optics, even in the face of overwhelming scientific evidence (and there wasn't huge sums of money involved).
To be fair, science along the traditional European model in previous centuries was much more hierarchical than it is today. Today there is such a broad range of funding sources, journals to publish in, and a vastly larger number of scientists, that it is hard for any one small group to dominate the discourse.
Yet their only evidence they present are fancy diagrams and graphs produced by experts who are never mentioned or sourced. So I tasked myself to find information and answers. Instead of anything solid all I find insinuation
Well, why don't you try reading some of the actual scientific papers? Go journals like Journal of Climate, Climate Dynamics, Journal of Geophysical Research, as well as the prestige journals like Science and Nature. Read the articles they have on the subject. Hunt for review articles for an overview. Or look at the latest IPCC report and the references therein.
Now, if there is so much debate over the models people are using (and are best weather model programs can't predict the weather a week in advance) how can they predict anything?
Climate models can predict over much longer timescales than weather models, because climate models only need to predict annual global averages, instead of specific temperatures over specific cities. Global averages over annual time scales are less sensitive to error.
And are these predictions accurate?
That depends on what you mean by "accurate". See, for instance, the variation in predictions for various models regarding global temperatures during this century (here). As you can see, there is a wide range of variation, but you can make general conclusions, such as "Warming is likely to continue, with a rate of 3.5 degrees C/century being the most likely".
I was told at Uni that we simply didn't know the effect of CO2 concentration on global temperatures (this by an "expert" University lecturer) now six years later we all of sudden have a solid indisputable understanding with rock solid models indicating we are all going to die.
We don't have "solid indistputable understanding" and our models are not "rock solid" and certainly do not indicate "we are all going to die". However, we do know a lot about the effect of CO2 concentration on global temperatures, and have for some time. Your lecturer was mistaken.
So my first thought was how can something so publicly accepted be contested so strongly and me not hear about this?
It's not contested as strongly as climate change skeptics and politicians would have you believe. For every paper contesting global warming there are literally hundreds of other papers that find evidence for it. It's true, however, that you can't rely on the media to give you a balanced presentation. Just read the scientific literature. It takes more work but it's the best source. You can get good information aimed at the layman on the RealClimate blog, written by a group of climatologists. It's not totally biased as skeptics would have you believe, either; they are quite frank in discussing what you can and
The function of the satellites is not to "prove" global warming. As you say, we already know the Earth is warming. If that's how the satellites are being represented, that is a real problem. Their most important actual role is to give us the data necessary to predict what the climate will do in the future, which is even more important than knowing what has happened to the climate in the past.
Why are Mars, Jupiter and Saturn experiencing global warming simultaneously with the Earth? They aren't. As far as can be determined, Mars has experienced regional warming near its south pole; there is no evidence for global warming. Furthermore, the warming trend was only over a 10 year period (or maybe even less, I don't remember); the Earth's climate itself fluctuates on those time scales. (For instance, it recently dropped 5 or 6 years in a row, despite the overall warming.) If that extends to a multi-decadal trend, and extends to the entire planet, then we might be able to say it's "global warming". Jupiter has the same issue; the temperature increase has only been regional, and only for a relatively short period of time. I haven't read anything about Saturn.
Then there is the issue of common causes, which is what you're claiming. The only climate factor that the planets share in common is solar output. Solar output does vary, but it its variations are known not to be large enough to be responsible for most of the global warming on Earth. They're also known not to be responsible for the warming on Mars, since solar output was undergoing a slight decrease during most of the duration of the observed polar warming. I don't know about Jupiter or Saturn.
In other words, quantum mechanics appears to almost always give right answers but it might as well be by elves smoke and mirrors. In other words, you think it's weird, and therefore untrustworthy. That's a nice opinion, but has nothing to do with the theory's actual validity.
When a photon is emitted, according to quantum, it sends out an instantaneous pilot wave in all directions and receies the information back as to deciding which way to go. You're speaking of Bohmian quantum mechanics, not any conventional interpretation of quantum theory. So it is not correct to say this is true "according to quantum [theory]".
Sorry to be like this, but can you provide a link to the results of an experiment that shows "everyone who measures its [light's] speed relative to themselves measures the same speed (c)." is true? The famous Michelson-Morley experiment did this; the Earth itself is moving at some speed, and they measured the speed of light in various directions relative to the Earth's motion, at different parts of the Earth's orbit as the Earth changed its direction (and speed), and found always the same value. There are also all the experiments which measure the speed of light emitted from a moving source, and find that it is independent of how fast the source is moving (see my experimental tests link above). There are also all of the indirect measurements which when combined with other indirect measurements, yield a direct estimate of the speed of light according to a moving observer (e.g., combining source independence with light-speed isotropy), not to mention all of other tested predictions of special relativity.
Of course it could be the result of a 'mere mechanical effect' if the only evidence is the atomic clocks slowing down when being flown round the world. That is not the only evidence. Steve Carlip (a quantum gravity theorist) has a good summary in response to someone on Usenet who made the same argument: If only one kind of clock — say, a particular type of atomic clock — slowed down, you would have a point. But as far as we can tell, every type clock, and everything else that changes with time, slows down, and all by exactly the same amount. We observe this for "clocks" based on weak interactions (e.g., particle decays), those based on electromagnetic interactions (e.g., atomic clocks), those based on strong interactions (e.g., other types of decays — though this is not really well tested for gravitational effects), those based on gravitational interactions (e.g., orbits in binary systems), as well as for "mechanical" clocks (e.g., rotating neutron stars). We believe that chemical reactions — and with them, human perceptions of time — will slow down by the same amount.
Now, you are free to invent some abstract concept of "time" that does not slow down. But if all physical processes slow down by the same amount in a gravitational field, that makes your "time" inherently unobservable. It's no longer what physicists mean by the word. Worse, it seems to be a useless concept: it can't be observed, it can't be affected, it has no effect on anything that can be observed.
To a physicist, if everything that changes with time slows down by the same amount under some condition, that means that time slows down.
Light doesn't travel faster than c, so anything you observe where it appears to move faster than c, has to be explained some other way, unless you decide to say that c is not the speed limit. What are you talking about? Light isn't observed to move faster than c.
I guess I just noticed what you meant by 'relativity' now, but I don't believe it would be measured at c relatively, only absolutely, Maybe you don't know what I meant by "relativity". The only thing you can ever measure in relativity is something's speed relative to you. There is no such thing as measuring a speed "absolutely". Light happens to be unique, in that everyone who measures its speed relative to themselves measures the same speed (c).
because if you could see light from any angle, and if you could move at the speed of light, then you'd be moving alongside the light beside you. You can't move at the speed of light. Nothing capable of measuring a speed can. A "light particle" can't measure the speed of another light particle, because no time passes for it. Einstein originally thought as you did — the original idea that led him to relativity was, "What would I see if I were riding a light beam?" — but eventually realized that the answer was more subtle.
What can be said is what I said earlier: pick any speed arbitrarily close to the speed of light, and an observer traveling at that speed will never come close to "moving along side the light", no matter how fast it goes: the observer will always observe the light receding from it at c.
Anyway I do tend to think people talking about space and 'time' warping, when I don't even believe in time, is silly. You may think it's silly, but its effects too have been measured. Whether you "believe in" time is irrelevant. You can fail to believe in time all you want, but clocks will still run slow, geodesics in spacetime will still curve in space, and so on. Those physical phenomena are what physicists mean by "curved spacetime", regardless of how you personally define "time" or its existence.
I believe that you can age at different rates depending on your velocity (possibly due to the fact that the electrons in the atoms which make up your body can't go faster than c, so if you're moving in one direction quickly then the orbit of the atom is slower at some points than it would be at rest) Our measurements of time dilation do not depend on the orbits of electrons changing speed, and anyway, without time dilation the period of the atom's orbit will not change no matter what speed it is moving. Time dilation is not a mere mechanical effect; it is fundamental to the nature of time.
Well he said that "strings" are not fundamental to the theory but emergent phenomena. Yes, but they emerge necessarily; they have to be part of the theory.
And as far as observing strings how do you independently observe the smallest thing in the universe? As others have noted somewhere else in the comments, you could say the same thing about quarks, which are the current "smallest thing in the universe". And in fact, no one has directly observed an isolated quark. But their presence can be revealed indirectly by scattering experiments. It's much harder with strings, since they are usually thought to be so much smaller than the scales we have probed. There are some scenarios in which the effective string scale is lowered, rendering stringy physics directly accessible. There are other scenarios in which high-energy string physics may be indirectly probed (e.g., cosmological observations of events that occurred near the Big Bang).
Both of those sites give a correct description of Hawking radiation (although the first one considers the case of the antiparticle falling in without explicitly mentioning that the particle can also fall in with equal probability). The latter paraphrase of Hawking agrees with what I said: the negative energy particle falls in (by definition). It's just that the negative energy particle can be the matter particle or the antimatter particle with equal probability — which one happens to fall in becomes the negative energy particle by virtue of falling in.
Does anything validate that particular point of the theory? The large number of experimental confirmations of relativity.
Inertiality isn't actually a word, and I would presume it means a state of staying still, so in fact your state of motion would be staying still. It means motion subject to no external forces, i.e., constant velocity. The speed of light is not well-defined in a non-inertial frame of reference; it can have any value between 0 and infinity.
The speed of light is different depending on the medium of its transit, and it does seem 'obvious' that if you had a proper measuring device and were travelling at near c yourself, then you would measure only a low speed for the speed of light that is moving in the same direction as you. It may seem "obvious", but it's wrong. That, again, is the point.
light doesn't have infinite speed, therefore if you are moving at the speed of light, the light next to you will appear immobile. That was Einstein's original thought experiment, but he found that the answer was not "light is at rest with respect to you", but "nothing capable of measuring the speed of light can travel at the speed of light". He also found that if you're traveling arbitrarily close to the speed of light, say 99.9999999% of c, that the light next to you will travel at c.
If it were possible to measure the speed of light with a radar gun, then it should be going slower if you are travelling in the same direction, and 'faster' if you were moving in the opposite direction. Except that doesn't actually happen. It's only "obvious" and logical if you make Newtonian assumptions about the nature of space and time. In relativity, the dual phenomena of time dilation and length contraction "conspire" to render the speed of light always c, no matter how fast you are moving.
I think A Brief History of Time did say that, because I always hear that claim from people who have read the book, but it's not actually true. Hawking was being too sloppy. It's true that one particle of the pair is always antimatter, but that's not always the one that falls in.
I'm not sure what you mean about 'the point'. By "the point" of relativity, I mean that its fundamental assumption is that light travels at the same speed with respect to all observers. It is the theory's main postulate. So the answer to the question is, no matter how you choose to measure the speed of light, and no matter what your state of motion is (assuming inertiality), you always get c, not half c or anything else.
What the hell are the strings made of? They're not "made of anything"; they are the fundamental objects that other things are made of. (This is analogous to the role of elementary particles in existing particle physics theories — they are not "made of" anything more fundamental, either.)
1) A string is defined on a background space. But gravity is supposed to be described by the string. So what's the background space???? i.e. what is the space that the string is floating in? (Related question: what's between strings?) The background space is a mathematical artifact which is physically unobservable. Physical measurements yield a dynamical spacetime just like in general relativity.
How about second quantization of string theory? In QFT, you can have an operator which creates new particles. What is the equivalent operator for creating new strings? First quantized string theory can create new strings in the sense that one string can break in two. There is second quantized string field theory, but it is unknown whether it is necessary to have such a theory.
The string landscape is huge, but so is the space of possible quantum field theories. People got false hopes when they believed that string theory would single out from first principles which particular solution to string theory is right. Now it appears that there may be no practical way of doing that within string theory, which leaves physicists in the situation of just having to pick out models that they hope will work, and test them against experiment the same old-fashioned way that particle physics theories have always been constructed.
Or is there any possible observation where one would say, if that observation is made, string theory is dead, period? There are some observations that you can't appear to get out of string theory; see the discussion of the string "swampland". But in general, string theory is as hard to falsify as is "quantum field theory". Nobody expects QFT to be falsified since it's a general consequence of broad assumptions about quantum theory and relativity, but it's possible to be falsified. String theory is slightly more falsifiable than the QFT framework, because string theories reduces to QFT at low energies but (via the swampland results) can't reduce to every possible QFT.
The main issue that is confused in the "string theory is unfalsifiable" debate is that people compare string theory to some specific QFT model like the Standard Model, where it should instead be considered as a generic framework in which to write down specific models, like QFT itself. You can construct easily falsifiable models within string theory, just like you can in QFT. But falsifying all of string theory is about as hard as falsifying the QFT framework itself.
Another major objection Smolin has to String theory is that it is "background dependent" like quantum theory: that is, it depends on the perspective of the observer, which flies in the face of Einstein's revolution. The mathematical formulation of perturbative string theory is background dependent, but its actual physical predictions give results that are observationally indistinguishable from Einstein's dynamical spacetime. In other words, no physical experiment can reveal this background; all observable physics in string theory behaves in a background independent way.
Furthermore, various sectors of string theory have fully background independent descriptions, although it is not known how to describe all of string theory in this way. Arguably, string theory is less background dependent than Einstein's general relativity, since Einstein assumes a spacetime of fixed dimensionality (and, under certain classical causality assumptions, topology) whereas string theory does not.
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I believe that research in the field would have sped up if Einstein hadn't so been so public in his denouncing it.
As far as I can tell, Einstein's arguments did nothing to slow research in the field. Most people were on Bohr's side by that time.
Slowly Bohr managed to win and lets face it the EPR paper was an embarresment, then whoom as you said everyonewas on the qm band wagon.
The EPR paper wasn't an "embarrassment", it remains one of the most important papers on foundational QM, and the QM bandwagon started as soon as Heisenberg published his paper.
I remember that the current BB model had to be revisited to account for new theories in QCD/QED.
The main influence that quantum field theory has had on Big Bang cosmology is that the Higgs boson inspired the invention of inflationary cosmology. Far from modifying the BB picture, inflation solved a number of its long-standing problems.
QFT has also had influences in other areas of now-accepted cosmology, such as dark matter, but that doesn't affect the Big Bang much.
I tried to locate the article and found this one. It's interesting what he has to say, especially about the shift in ideas. I don't know much about the physics (nor, sadly the time to get into again) to say one way or the other. Maybe you've heard of it. If so what do you think? http://www.rense.com/general53/bbng.htm
Lerner is a pretty well known crackpot. (See Ned Wright's discussion here. He and Lerner had a back-and-forth and Wright eventually gave up arguing with him.) On the list of signatories are other people like the founders of Steady State cosmology, a theory which failed decades ago.
As for the scientific criticisms, yes Big Bang cosmology needs inflation and dark matter. One man's "fudge factor" is another's new theory. It's absurd to claim that BB cosmology has not made any predictions; it predicts an expanding universe, the existence and blackbody spectrum of the CMBR, light-element nucleosynthesis rate ratios, it accounts for measurements of luminosity-redshift curves, it predicts hotter temperatures in the past which have been observed, and so on. Inflation makes specific predictions about the statistical power distribution of the CMBR spectrum which have been confirmed. Dark matter has a wide range of evidence in its favor from galactic rotation to clusters to large-scale structure formation to cosmology. Furthermore, it is now known that candidate particles for the inflaton and dark matter appear naturally in almost every extension to the Standard Model that people have thought up — and not because they were added in explicitly to serve as inflatons or dark matter — including some in the Standard Model itself; inflation and dark matter could be predicted on the basis of particle physics alone.
During my four years at Uni I was told the models for neutron stars, planetary creation etc were constantly under debate to match observations with newer technology. Fair enough, I'm the first to say we can't know everything about a system and that we need to rethink when new data is found, but my point is if so many of our models are under doubt then why are our climate models so trustworthy?
Well, for one, they don't depend on unknown physics like the behavior of quantum chromodynamics at high densities. They also are based on far more data than we have about stellar interiors.
That being said, our current climate models aren't terribly accurate, by most physics standards. But climatologists have found that they get decent results when they average the predictions of an ensemble of climate models. In short, it's not the case that we can't use models accurately. Their predictions vary (I showed you graphs of that), but model calibration studies give reason to believe that the true values fall somewher
I read recently that advents in QCD / QED have brought the Big Bang and the current mathematical models for Black Holes under doubt. I've not heard anything like that, and I came out of the gravitational physics field. But if you can point me towards a source, I can tell you what I think.
I know what you mean, being an ex-theoretical physicist myself, but I should note that climatology really is primarily physics (plus chemistry, and some economics mixed in for emissions forecasts), even if it is usually done in department that doesn't have "physics" in its name. It's a bit more comparable to astronomy than traditional "physics", since they often have only sparse observational data with large error bars.
Honestly, it's very hard for students at that level to usefully evaluate the evidence in such a field; it would probably take a year of dedicated study to get a handle on the real issues. Sadly, it's hard to get away from "the experts said so" without further scientific background.
You can find decent if sketchy summaries of some of these issues on the Wikipedia pages on global warming, GIS and WAIS, etc.
By the way, what subject do you teach, and at what level?
You will note that the global warming on Pluto is attributed to it recently having been at its closest approach to the Sun, which has nothing to do with global warming on Earth. (But maybe you were just joking, I'm not sure.)
I know (first hand) what research scientists will do for grant money, but you're right it would be a little hard to conceive of it on this scale.
You can get grant money for results which challenge the status quo. In fact, you can get a lot of grant money this way, as long as you can back up your claims. On a more mundane level, you can certainly get grant money for work that reevaluates the reliability of climate models, temperature reconstructions, etc.
It has happened in the past with Newton's theories of light, for over a hundred years the Royal Society refused to accept anything that went against Newtonian optics, even in the face of overwhelming scientific evidence (and there wasn't huge sums of money involved).
To be fair, science along the traditional European model in previous centuries was much more hierarchical than it is today. Today there is such a broad range of funding sources, journals to publish in, and a vastly larger number of scientists, that it is hard for any one small group to dominate the discourse.
Yet their only evidence they present are fancy diagrams and graphs produced by experts who are never mentioned or sourced. So I tasked myself to find information and answers. Instead of anything solid all I find insinuation
Well, why don't you try reading some of the actual scientific papers? Go journals like Journal of Climate, Climate Dynamics, Journal of Geophysical Research, as well as the prestige journals like Science and Nature. Read the articles they have on the subject. Hunt for review articles for an overview. Or look at the latest IPCC report and the references therein.
Now, if there is so much debate over the models people are using (and are best weather model programs can't predict the weather a week in advance) how can they predict anything?
Climate models can predict over much longer timescales than weather models, because climate models only need to predict annual global averages, instead of specific temperatures over specific cities. Global averages over annual time scales are less sensitive to error.
And are these predictions accurate?
That depends on what you mean by "accurate". See, for instance, the variation in predictions for various models regarding global temperatures during this century (here). As you can see, there is a wide range of variation, but you can make general conclusions, such as "Warming is likely to continue, with a rate of 3.5 degrees C/century being the most likely".
I was told at Uni that we simply didn't know the effect of CO2 concentration on global temperatures (this by an "expert" University lecturer) now six years later we all of sudden have a solid indisputable understanding with rock solid models indicating we are all going to die.
We don't have "solid indistputable understanding" and our models are not "rock solid" and certainly do not indicate "we are all going to die". However, we do know a lot about the effect of CO2 concentration on global temperatures, and have for some time. Your lecturer was mistaken.
So my first thought was how can something so publicly accepted be contested so strongly and me not hear about this?
It's not contested as strongly as climate change skeptics and politicians would have you believe. For every paper contesting global warming there are literally hundreds of other papers that find evidence for it. It's true, however, that you can't rely on the media to give you a balanced presentation. Just read the scientific literature. It takes more work but it's the best source. You can get good information aimed at the layman on the RealClimate blog, written by a group of climatologists. It's not totally biased as skeptics would have you believe, either; they are quite frank in discussing what you can and
The function of the satellites is not to "prove" global warming. As you say, we already know the Earth is warming. If that's how the satellites are being represented, that is a real problem. Their most important actual role is to give us the data necessary to predict what the climate will do in the future, which is even more important than knowing what has happened to the climate in the past.
Then there is the issue of common causes, which is what you're claiming. The only climate factor that the planets share in common is solar output. Solar output does vary, but it its variations are known not to be large enough to be responsible for most of the global warming on Earth. They're also known not to be responsible for the warming on Mars, since solar output was undergoing a slight decrease during most of the duration of the observed polar warming. I don't know about Jupiter or Saturn.
If only one kind of clock — say, a particular type of atomic clock — slowed down, you would have a point. But as far as we can tell, every type clock, and everything else that changes with time, slows down, and all by exactly the same amount. We observe this for "clocks" based on weak interactions (e.g., particle decays), those based on electromagnetic interactions (e.g., atomic clocks), those based on strong interactions (e.g., other types of decays — though this is not really well tested for gravitational effects), those based on gravitational interactions (e.g., orbits in binary systems), as well as for "mechanical" clocks (e.g., rotating neutron stars). We believe that chemical reactions — and with them, human perceptions of time — will slow down by the same amount.
Now, you are free to invent some abstract concept of "time" that does not slow down. But if all physical processes slow down by the same amount in a gravitational field, that makes your "time" inherently unobservable. It's no longer what physicists mean by the word. Worse, it seems to be a useless concept: it can't be observed, it can't be affected, it has no effect on anything that can be observed.
To a physicist, if everything that changes with time slows down by the same amount under some condition, that means that time slows down. Light doesn't travel faster than c, so anything you observe where it appears to move faster than c, has to be explained some other way, unless you decide to say that c is not the speed limit. What are you talking about? Light isn't observed to move faster than c.
What can be said is what I said earlier: pick any speed arbitrarily close to the speed of light, and an observer traveling at that speed will never come close to "moving along side the light", no matter how fast it goes: the observer will always observe the light receding from it at c. Anyway I do tend to think people talking about space and 'time' warping, when I don't even believe in time, is silly. You may think it's silly, but its effects too have been measured. Whether you "believe in" time is irrelevant. You can fail to believe in time all you want, but clocks will still run slow, geodesics in spacetime will still curve in space, and so on. Those physical phenomena are what physicists mean by "curved spacetime", regardless of how you personally define "time" or its existence. I believe that you can age at different rates depending on your velocity (possibly due to the fact that the electrons in the atoms which make up your body can't go faster than c, so if you're moving in one direction quickly then the orbit of the atom is slower at some points than it would be at rest) Our measurements of time dilation do not depend on the orbits of electrons changing speed, and anyway, without time dilation the period of the atom's orbit will not change no matter what speed it is moving. Time dilation is not a mere mechanical effect; it is fundamental to the nature of time.
Both of those sites give a correct description of Hawking radiation (although the first one considers the case of the antiparticle falling in without explicitly mentioning that the particle can also fall in with equal probability). The latter paraphrase of Hawking agrees with what I said: the negative energy particle falls in (by definition). It's just that the negative energy particle can be the matter particle or the antimatter particle with equal probability — which one happens to fall in becomes the negative energy particle by virtue of falling in.
I think A Brief History of Time did say that, because I always hear that claim from people who have read the book, but it's not actually true. Hawking was being too sloppy. It's true that one particle of the pair is always antimatter, but that's not always the one that falls in.
The string landscape is huge, but so is the space of possible quantum field theories. People got false hopes when they believed that string theory would single out from first principles which particular solution to string theory is right. Now it appears that there may be no practical way of doing that within string theory, which leaves physicists in the situation of just having to pick out models that they hope will work, and test them against experiment the same old-fashioned way that particle physics theories have always been constructed.
The main issue that is confused in the "string theory is unfalsifiable" debate is that people compare string theory to some specific QFT model like the Standard Model, where it should instead be considered as a generic framework in which to write down specific models, like QFT itself. You can construct easily falsifiable models within string theory, just like you can in QFT. But falsifying all of string theory is about as hard as falsifying the QFT framework itself.
Furthermore, various sectors of string theory have fully background independent descriptions, although it is not known how to describe all of string theory in this way. Arguably, string theory is less background dependent than Einstein's general relativity, since Einstein assumes a spacetime of fixed dimensionality (and, under certain classical causality assumptions, topology) whereas string theory does not.