Are we all really just an illusion?
And thanks for a very interesting thread.
Are you perchance thinking of this?
I wouldn’t say it is incorrect to claim that light travels through reality; I’m just not sure if such a statement is all that useful. Perhaps a bit more concrete would be to say that light travels through spacetime, but even then, spacetime is so fundamental to the concept of “traveling” that this claim doesn’t provide much insight. (That is: of course light moves through spacetime because traveling through spacetime is how we define “move”.) The important point is that we have no evidence that light is a ripple of (or is tied to) some medium. In constrast, a sound wave, say, is an almost abstract thing on top of some medium – the material (e.g., air) already exists, and if its constituent atoms move just right, you get phenomena that we describe as (sound) waves. Our description of light doesn’t have any such underlying material.
On the part about alternating between “light energy and magnetic field energy”… The classical decsription of electromagnetism relies heavily on the concept of electric and magnetic fields. If you have a charged particle sitting somewhere, the influence it has on other charged particles can be encapsulated in a mathematical construct called “electric field”. Same thing with magnetism: if you have a moving charged particle, the influence it has on other moving charged particles can be encapsulated by a mathematical construct called “magnetic field”.
The equations that describe these fields (Maxwell’s equations) naturally include “source” terms. That is, the fields at any given point are functions of the source charges that exist and how those charges are changing. It turns out, though, that if you set all the sources to zero, the equations still permit a certain type of electric and magnetic field. This special free-space (i.e., no charges) solution has the particular form, namely: an oscillating electric field alongside an oscillating magnetic field, with the resulting waveform traveling at some fixed speed c. A charged particle some far distance away can be influenced by this wave when it gets there, so energy and momentum are being transported. This moving bundle of energy/momentum/ability-to-influence-charges gets labeled an EM wave, or more casually, light.
I assume that the text you were reading was attempting to relate this concept? The quantum electrodynamics (QED) description of light doesn’t think of electric and magnetic fields in quite the same way, although the photon in QED is described mathematically as a field.
Not sure what to say about this, but I’m willing to give it a try if you could expand a bit. For now: light isn’t all that special in the universe. If you turned off light in the universe, the universe would still exist (at least given our current descriptions of things.)
Yes, I think so, and your magnetism example is a good one. Indeed, as long as two descriptive approaches give the same answers, there’s no way to say that one is “right” and one is “wrong”.
Haven’t heard that one. Sounds a bit like an urban legend to me, too.
You can take the red pill to find out. 
Since the LHC is probably the largest accelerator that will ever be affordable, further advances in beam energy will require new technologies. Are things like using synchonized lasers or plasma waves a viable possibility?
To achieve a theory that unfies/supercedes General Relativity and Quantum Physics, do you think GR will have to be modified to fit QM more closely, or vice-versa?
What’s your favorite maverick “wouldn’t this be cool if it were real” alternate theory?
Are magnetic monopoles a dead end in current research?
Is the weak force almost certainly a fundamental force, or could it be just a manifestation of a deeper force? I’m thinking of an analogy with how pions were once considered the boson of the Strong force which bound nucleons, until it became clear that quarks/gluons were the deeper explanation.
Pasta, thanks for doing this.
Quantum entanglement. Layman’s terms, if that is even possible.:dubious:
Since the LHC is probably the largest accelerator that will ever be affordable, further advances in beam energy will require new technologies. Are things like using synchonized lasers or plasma waves a viable possibility?
I think so. As background for others: the largest particle accelerators today boost their payload with oscillating electric fields in a resonating “radiofrequency cavity” (RF cavity pic #1, RF cavity pic #2). The RF part of the name just indicates that the field oscillates at, well, radio frequencies. In a circular accelerator like the LHC, the idea is to time the oscillations so that a particle making a complete loop around the ring and returning to a cavity gets there just in time to see:
(a) an electric field pushing it in its direction of travel (acceleration), or
(b) an electric field pushing it against its direction of travel (deceleration), or
(c) no significant electric field (storage).
The energy gain a particle receives in each “cavity crossing” is limited by the maximum electric field strength in the cavity. This, in turn, is limited by the breakdown voltage of the cavity materials. To get to higher energies, you can squeeze a little more out of RF cavity design or you can build bigger accelerators with more cavities around the ring (expensive).
A new technology being developed, called plasma wakefield acceleration, gets its electric fields a different way. You start with a plasma (hot gas of electrons and positive ions) and you disturb the spatial charge distribution of the plasma using a laser or electron pulse. The goal is to make one side heavy on the negative charges, and the other heavy on the positive. A packet of beam electrons passing through during this disturbed moment will feel the electric field set up by the spatial imbalance of charge. And, since this electric field is localized (and away from the walls of the plasma cavity), it can be quite large without running into materials limits.
Prototype wakefield accelerators have had good success. The next step is to apply these in the real world (small-size middle-energy setups). The hope would be that one could subsequently scale the technology up to the energy frontier, but there are quite a few baby steps to take between here and there.
Asides on RF cavities:
The above description of RF cavities leads to a corollary: RF-accelerated beams are not continuous beams; the payload is pulsed. Picture a stored particle making its way around the ring. This particle must encounter no electric fields in the RF cavities, and the oscillations in the cavities are phased up to make this so. Now picture a hypothetical particle in the ring trailing behind the first particle. Say it is far enough back that it reaches each cavity a quarter of an RF cycle later than the first. This particle will see a large electric field and will be accelerated. Again in the next cavity. And again. Soon, it will actually catch up with the first particle. It will then overtake it, but it will also then see opposing fields as it reaches the RF cavities too early. In the end, all stored particles settle stably* inside RF oscillation “buckets”. Thus, the delivered beam comes in pulses, in time with the RF oscillations. (An additional corollary you might notice is that the ring has a fixed number of buckets it holds in its circumference.)
*there are challenges, of course, in getting particle trajectories to dampen down into the desired, stable path.
To achieve a theory that unfies/supercedes General Relativity and Quantum Physics, do you think GR will have to be modified to fit QM more closely, or vice-versa?
Current efforts lean toward describing gravity in analogy with particles physics. I’m not sure I’ve ever heard of anyone attempting the other direction (describing particle physics in a framework analogous with GR). Even in the first case, though, I wouldn’t expect the unification to contain a sort of “modified GR”. My guess is that GR would stay put, and a wholly unrelated description of gravity would be invoked. But, developing unified theories is far from my realm of expertise!
What’s your favorite maverick “wouldn’t this be cool if it were real” alternate theory?
I’m not one for favorites. But, wouldn’t stable wormholes be pretty cool?
Are magnetic monopoles a dead end in current research?
I wouldn’t say that monopole searches (or any exotic searches) are a dead end. Grand unified theories often predict their existence, although usually at much higher energies than we can probe, but those theories don’t have to be right, so I say: if it excites you, keep looking for it. I’m not up on the latest in this small subfield, though.
Is the weak force almost certainly a fundamental force, or could it be just a manifestation of a deeper force?
It could be anything. True, we have no good evidence for any substructure at the moment. But, I think the words “certainly” and “fundamental” rarely make sense together in any sentence.
Quantum entanglement. Layman’s terms, if that is even possible.
Take some quantum characteristic of a particle, say its spin. For an electron, spin can have one of two values, which we’ll label plus and minus.
A central theme of quantum mechanics is that you can have an electron whose spin is not well-defined. Rather, this electron is half in the plus spin state and half in the minus spin state, and up until the point that you measure the spin, either answer is possible. You should not think of this scenario as “the electron has a specific spin, but I don’t know which one until I measure it.” It is experimentally demonstrable that the scenario is actually that “the electron doesn’t have a well-defined spin yet, and both answers are possible for this single electron, and when I measure it, that answer will become the electron’s spin.” (The process of measurement is an active one, so this shouldn’t sound magical. That is, to measure is to interact, so physics can happen during the measurement process.)
Entanglement makes things one step weirder. Instead of preparing a single electron to be in this so-called “superposition” of spin states, you can prepare two electrons. And, if you choose the right preparation process, you can also rely on a conservation law to ensure that the spins of the two electrons must be opposite. That is, if one is plus, the other must be minus. But now you’ve created two electrons that each have undetermined spin but when you determine the spin of one of them, the other (I’ve claimed) must be opposite. Picture the conundrum: you prepare these two electrons and send them far apart from each other, to different rooms even. It can be shown that electron A and electron B indeed both have unspecified spins – both answers are still possible at a fundamental level. However, if two lab techs in these two rooms measure the spins now, they will always get opposite answers, even if there isn’t time for a message to travel from one electron to the other. In other words, the system of electrons had two possible states: A=plus/B=minus or A=minus/B=plus. Measuring just electron A to be, say, plus removes the possibility of measuring B to be plus.
This is similar to the single electron case (where the electron was simultaneously in the plus and minus states), except now our two electrons are simultaneously in multiple states in a correlated way. The electrons are said to be “entangled”.
All helpful. I am torn between the special properties of light - its partcle/wave nature; its fundamental constant speed as you describe in the oscillating fields explanation above - and your closing statement “if you turn it off, stuff is still there.” it feels like it is a cornerstone to our universe, but it’s just a thing within it.
For now I’m gonna clam up unless I can find a better way to articulate my ignorance so you can fight it some more
The special properties of light are actually special properties of the universe. Electrons are also particle/wave things. And protons. And everything else. Also, the special speed that falls out of Maxwell’s equations isn’t there because those equations deal with light. Think of it the other way – c is fundamental to the universe, and light (being a massless thing in the universe) travels at that speed. Gravitational waves travel at c. Massive particles can travel at any speed up to c.
It is unfortunate that c is called “the speed of light” since it is not special to light at all. That is, the poor choice of name for c should not be taken to mean that light in fundamental to the fabric of the universe. It is a mere passenger in a universe that happens to have a speed limit.
(In fact, c is only a speed at all because space and time were originally treated on very different footing. When we learned that space and time were intimately related and, in fact, just separate dimensions in “spacetime”, we needed a unit conversion between human-imposed distances and times. That unit conversion is c. When doing particle physics (or a number of other fields), one in fact chooses a different system of units wherein distance and time are on equal footing, and c=1 (a unitless number). In these so-called “natural units”, distance and time have the same units, mass and energy have the same units, and speeds vary from 0 to 1 (no units).)
I have a hard time imagining how this could be done. Just how far apart could we send these two electrons anyway?
Any distance not to exceed the interval t times c. Entanglement has been experimentally verified at distances of thousands of kilometers, but there is no theoretical maximum.
Stranger
For anyone for whom this could be a whoosh, Stranger’s point is simply that while entanglement doesn’t care how far apart you send the electrons, there is an unrelated practical limit. Namely, if you want to send them really far apart, you have to wait for them to get there (which is limited by how fast they are going, which is limited by c.)
How much optimism do you have for economically-viable controlled fusion in the next few years? Do you consider it at all possible that using muons as nuclear catalysts would be the key factor? That is to say, can the obstacles to success by this route be overcome?
Have you seen Futurama? Do you like it?
Brian
Quantum Leap and The Twilight Zone have given us popular notions of the Many Worlds Theory, or, as Terry Pratchett would say, something with trousers. How does this theory hold up today? Do physicists still believe that particles split into two universes upon measuring (or have they ever?), and if so, how does this relate to the world at macro level? Is there really a clone of me in another dimension?
Years ago I read something about an analogue computer, where quantum states would be used for computer cycles, making these computers infinitely faster than regular ones. Do you know the latest development on this?
I often say there are no stupid questions; only stupid people. I am an excellent example of someone both profoundly stupid and possibly unteachable on the topic of physics. Yet I plod on:
I am much more interested in the nature of space than of particles and energy; until we clarify what space is, to me we’re just bumbling around trying to define particles and energy.
If we find evidence for the Higgs boson, will that lend real credence to the Higgs field as a way of understanding what space itself is, or will it simply fill in a gap for a model that needs to find a way to generate mass, but leave us with no better understanding of space itself?
And as a second question: are there models which suggest that space–whether it’s a Higgs condensate or some other non-nothingness–is not completely smooth at a macro level? Could gravity, as an example, be caused by a difference in the “density” of space, so to speak?
Would it be possible to transmit information this way, though? I assume that you can’t actually know that an electron is measured or not without measuring it, which means that simply knowing that the entangled electron must be plus or minus doesn’t actually enable me to transmit information.
This is helpful - thanks again. I am reading **"The Making of the Atomic Bomb" by Richard Rhodes ** (Amazon link) and really enjoying it, so this thread is particularly germane for me. I am just getting to Bohr’s model of the atom and the building of the first particle accelerators…cool stuff.
How much optimism do you have for economically-viable controlled fusion in the next few years? Do you consider it at all possible that using muons as nuclear catalysts would be the key factor? That is to say, can the obstacles to success by this route be overcome?
In the next few years? Impossible. This century? I’m optimistic, but it isn’t guaranteed.
The challenges are manifold. A few:
- The intense neutron flux makes most materials brittle after some time (and that time isn’t well known).
- Radioactivation of materials also presents an engineering challenge (e.g., you need to know which parts will require regular replacement, and you need to be able to replace them without getting anywhere near them.)
- Production of energy does not imply extraction of that energy in a usable form. Neutrons carry away most of the energy, so you need a workable design for stopping those neutrons, turning that energy into work (probably via a steam turbine), and dealing with any by-products.
- Tritium is produced abundantly, and a commercial design would likely need to capture and process all of this.
- Long-term plasma confinement (with a fusion reaction taking place) has never been achieved.
ITER is the next big engineering prototype. The plan is to maintain a better-than-break-even fusion reaction in a magnetically confined plasma for up to eight minutes. However, the numerous R&D goals are arguably more important (studying materials issues, vacuum vessel design, primary magnet design, confinement control/tuning, …). If all goes well, ITER will start running in 2018. The next step after ITER could be the DEMO project, which aims to produce electrical power continuously. It would run sometime around 2040.
However, it only takes one unsolved engineering challenge to push these times arbitrarily into the future. Based on the results of past fusion projects, I would anticipate at least one unexpected problem, but perhaps not many. So, my fairly uneducated guess would put widespread commercially available fusion power sometime around the end of the century.
Have you seen Futurama? Do you like it?
Yes and yes. I don’t watch TV much, but when I do, I’ve been known to stop my channel surfing at Futurama.
Quantum Leap and The Twilight Zone have given us popular notions of the Many Worlds Theory, or, as Terry Pratchett would say, something with trousers. How does this theory hold up today? Do physicists still believe that particles split into two universes upon measuring (or have they ever?), and if so, how does this relate to the world at macro level? Is there really a clone of me in another dimension?
Quantum mechanics has been interpreted in many ways, and the “many worlds” interpretation is but one of these. While the various interpretations offer different intuitive advantages or (subjective) elegance, they are all consistent with observation. Thus, no one can claim that one is more “right” than another. The “many worlds” interpretation gets a lot of airtime particularly because it is easy to think about.
The real advantage to exploring multiple QM interpretations is that these can guide searches for new physics. For example, if the universe does/ split into two, one can naturally ask if the two new universes have any connection to one another. It doesn’t appear that they do, but following up on ideas like this sometimes leads to breakthroughs.
Years ago I read something about an analogue computer, where quantum states would be used for computer cycles, making these computers infinitely faster than regular ones. Do you know the latest development on this?
I haven’t stayed up to date in the last few years, but the concept you are thinking of is quantum computing. At the heart of it all is that quantum systems evolve under different rules than classical systems and involve different mathematics. This means that a single quantum operation can induce changes to a collection of bits that would take many operations on a classical computer. (Example classical operations: addition, bitshifting. Quantum operation: rotation of N-vector.) If one can design algorithms that take advantage of quantum operations, one can solve certain problems more quickly. The usual example is integer factorization, for which a quantum algorithm has been designed (Shor’s algorithm) and implemented.
So far, quantum computers only consist of handfuls of bits in laboratories. It’ll be some time before you can buy a Dell Quantum XC5.
If we find evidence for the Higgs boson, will that lend real credence to the Higgs field as a way of understanding what space itself is, or will it simply fill in a gap for a model that needs to find a way to generate mass, but leave us with no better understanding of space itself?
Observing the Higgs will not clarify what space is. Space is a given in the Standard Model, and no attempt is made at describing any substructure for it. (The Higgs lives in space.) As you say, the Higgs mechanism offers us mass, and this mechanism requires that there is at least one Higgs particle, so we can look to see if it’s there.
And as a second question: are there models which suggest that space–whether it’s a Higgs condensate or some other non-nothingness–is not completely smooth at a macro level? Could gravity, as an example, be caused by a difference in the “density” of space, so to speak?
Theories with discrete space are popular. Nothing we’ve seen requires it, but nothing disallows it either, and it is an active area of theoretical research. I’m not up on the latest, unfortunately, so I don’t think I can comment usefully on the second part (whether a concept of “space density” can be invoked to yield something like gravity). But, I haven’t seen anything like that.
[Regarding entanglement] Would it be possible to transmit information this way, though? I assume that you can’t actually know that an electron is measured or not without measuring it, which means that simply knowing that the entangled electron must be plus or minus doesn’t actually enable me to transmit information.
Exactly right. You cannot transmit any information, as you deduced.
It should be noted that the “Multiverse” conception common in science fiction bares only a passing resemblance to the DeWitt “Many Worlds Interpretation”, and none at all to Hugh Everett’s “Relative State” hypothesis. In essence what this interpretation provides is a way to get around the seemingly artificial mathematical formalism of probability waveform collapse, and the attendant requirement for an observer-initiated event and the apparent paradoxes this entails, i.e. Schrödinger’s cat, Wigner’s Friend, the Einstein-Rosen-Podolsky paradox, et cetera. Instead of ascribing the action of the system to a collapse event as seen/caused by a classical observer (initially isolated from the quantum system), Relative State/Multiverse assumes that the observer and all connective linkages (any measurement and communication instrumentation) are embedded in the same quantum system as the part of the system which is under investigation, and so the quantum states of all parts of the system are entangled and exist in a unique correlation for any given condition. Instead of an initial collapse, the waveforms remain intact, and the observer sees the system in relative state, i.e. as it already relates to the quantum state of the observer and connection. It’s sort of like floating in the ocean and seeing a ball floating up and down as the waves crest; it may seem that the movement of the ball and the timing of when it can be observed is independent of the swimmer, but in fact the swimmer is embedded in the same waveform as the ball such that when he can observe the ball is predicated on the frequency and phase of the ocean waves.
However, in order to satisfy the necessity of an apparently stochastic (non-deterministic) system, it is necessary to superimpose an entire spectrum of waveforms such that the position at any given time of one measurement on a waveform is predicated on the position of all other waveforms in the system, ad nauseam, so in order to predict the state of the system you’d have to know the state and relationship of all other parts of the system, which is not possible because whatever you’re using to model the system is embedded within the system itself, and therefore is more complicated than the system. The only part of the system that can be observed is the local system (that with which you interact with and observe directly), and it is not uniquely correlated to any other isolated part of the system. That is, for any combination of finite parameters, there are an infinite number of potential states for the system.
So the overall system (i.e. the Universe) that we perceive is just one composite waveform, of which they are an infinite number. Whether these other universes actually exist and have some variation of ourselves running around inside them, making all manner of decisions that almost, but not quite, entirely unlike any choices we would make, or whether they’re just an abstract formulation of hypothetical probabilities that are not substantiated is itself subject to interpretation. In one particular casting of this interpretation, our own waveform is the only one endowed with energy; all others are a kind of external residue, sort of an imaginary remainder. In others, all possibilities have independent energy, or share from the same fund of energy in accordance with their probabilities, and only the states with high (i.e. internally consistent) probabilities have enough energy to instantiate. In no case is it possible to travel from one to another, or even communicate information between them any more than it is for the swimmer above to hop from crest to crest of the waves without swimming in the intervening troughs, nor does every choice result in a physical branching of the universes, as this would strongly violate conservation of energy (unless there is some external fund of infinite energy).
As Pasta notes, this is just one interpretation of QM among many, and none of them yield predictions that allow one to be experimentally distinguished (falsified) from another. The advantage of Relative State is that you get to have local realism and determinism i.e. things really exist even when an observer is not interacting with them, and the apparent randomness is actually just an artifact of the underlying complexity of the system. You also get to dispense with any initial conditions, propagating wavefronts, spontaneous collapse, non-local connectivity, anthropic interpretations, or any of the other seemingly mystical phenomena associated with decoherence/collapse interpretations. The disadvantage is that there is no way for the observer (who is innately embedded within the particular collection of waveforms that makes up his reality) to distinguish his uncollapsed instantiation from a collapsed state interpretation; for him, it is just the single reality that he can observe.
Which interpretation you choose is really dependent upon what appeals to your aesthetically and philosophically, not what can be literally tested.
Stranger