A bit ago, the news streams were once again abuzz with claims that NASA was investigating amazing space drives that violate the laws of physics. And it’s true! If we grant that “NASA” includes “any person employed by NASA,” and “investigating” is defined as “wasting time and money thinking about.”
I say “again” because it was only a few years ago that news spread about a NASA effort aimed at a warp drive, a way to truly break the speed-of-light limit. Of course there are no realistic scenarios along those lines, so the investigators didn’t have any tangible results to present. Instead, they did the next best thing, releasing an artist’s conception of what a space ship powered by their (wholly imaginary) warp drive would look like. (What remains unclear is how the warpiness of the drive affected the design of their fantasy vessel.)
The more recent “news” is not actually about warp drive at all. It’s about propellantless space drives — which are, if anything, even less believable than the warp drives. (There is a whole zoo of nomenclature devoted to categorizing all of the non-existent technologies of this general ilk, which I won’t bother to keep straight.) Warp drives at least inspired by some respectable science — Miguel Alcubierre’s energy-condition-violating spacetime. The “propellantless” stuff, on the other hand, just says “Laws of physics? Screw em.”
You may have heard of a little thing called Newton’s Third Law of Motion — for every action there is an equal and opposite reaction. If you want to go forward, you have to push on something or propel something backwards. The plucky NASA engineers in question aren’t hampered by such musty old ideas. As others have pointed out, what they’re proposing is very much like saying that you can sit in your car and start it moving by pushing on the steering wheel.
I’m not going to go through the various claims and attempt to sort out why they’re wrong. I’m not even an engineer! My point is a higher-level one: there is no reason whatsoever why these claims should be given the slightest bit of credence, even by complete non-experts. The fact that so many media outlets (with some happy exceptions) have credulously reported on it is extraordinarily depressing.
Now, this might sound like a shockingly anti-scientific attitude. After all, I certainly haven’t gone through the experimental results carefully. And it’s a bedrock principle of science that all of our theories are fundamentally up for grabs if we collect reliable evidence against them — even one so well-established as conservation of momentum. So isn’t the proper scientific attitude to take a careful look at the data, and wait until more conclusive experiments have been done before passing judgment? (And in the meantime make some artist’s impressions of what our eventual spaceships might look like?)
No. That is not the proper scientific attitude. For a very scientific reason: life is too short.
There is a more important lesson here than any fever dreams about warp drives: how we evaluate scientific claims, especially ones we encounter in the popular media. Not all claims are created equal. This is elementary Bayesian reasoning about beliefs. The probability you should ascribe to a claim is not determined only by the chance that certain evidence would be gathered if that claim were true; it depends also on your prior, the probability you would have attached to the claim before you got the evidence. (I don’t think I’ve ever written a specific explanation of Bayesian reasoning, but it’s being discussed quite a bit in the comments to Don Page’s guest post.)
Think of it this way. A friend says, “I saw a woman riding a bicycle earlier today.” No reason to disbelieve them — probably they did see that. Now imagine the same friend instead had said, “I saw a real live Tyrannosaurus Rex riding a bicycle today.” Are you equally likely to believe them? After all, the evidence you’ve been given in either case is pretty equivalent. But in reality, you’re much more skeptical in the second case, and for good reason — the prior probability you would attach to a T-Rex riding a bicycle in your town is much lower than that for an ordinary human woman riding a bicycle.
The same thing is true for claims about new technology. If someone says, “NASA scientists are planning on sending a mission to Jupiter’s moon Europa,” you would have no reason to disbelieve them — that’s just the kind of thing NASA does. If, on the other hand, someone says “NASA scientists are building a space drive that violates Newton’s laws of motion” — you should be rather more skeptical.
Which is not to say you should be absolutely skeptical. It’s worth spending five seconds asking about what kind of evidence for this outlandish claim we have actually been given. I could certainly imagine getting enough evidence to think that momentum wasn’t conserved after all. The kind of thing I would like to see is highly respected scientists, working under exquisitely controlled conditions, doing everything they can to be hard on their own work, subjecting their experiments to intensive peer review, published in refereed journals, and ideally replicated by competing groups that would love to prove them wrong. That’s the kind of thing we got, for example, when the Higgs boson was discovered.
And what do we have for our propellantless space drive? Hmm — not quite that. No refereed publications — indeed, no publications at all. What started the hoopla was an article on a web forum called NASAspaceflight.com. Which sounds kind of respectable, until you notice it isn’t affiliated with NASA in any way. And the evidence that the article points to is — wait for it — a comment on a post on a forum on that very same web site. Admittedly, the comment was written by someone who actually does work for NASA. But, not to put too fine a point on it, lots of people work for NASA. The folks in this particular “Eagleworks” group at Johnson Spaceflight Center are a group of enthusiasts who feel that gumption and a bit of elbow grease might possibly enable them to build spaceships that do things beyond what the laws of physics might naively let you do.
And good for them! Enthusiasm is a virtue. Less virtuous is taking people’s enthusiasm at face value, rather than evaluating claims soberly. The Eagleworks group has succeeded in producing, essentially, nothing at all. Their primary mode of communication seems to be on Facebook. NASA officials, when asked by journalists for comment on the claims they leave on websites, remain silent — they don’t want to have anything to do with the whole mess.
So what we have is a situation where there’s a claim being made that is as extraordinary as it gets — conservation of momentum is being violated. And the evidenced adduced for that claim is, how shall we put it, non-extraordinary. Utterly unconvincing. Not worth a minute’s thought. Let’s get on with our lives.
Daniel Kerr: “You supplied the calculation yourself and made an error.”
You know I have made an error but you wouldn’t tell me what the error is? Becoming more and more correct?
Pentcho, Daniel does not know the details of your calculation per his last comment, so he can not tell you which of many possible errors you made. Perhaps if you give the details and ask nicely he will explain where the error is. However, it would be better for your development to read the article he cited (again, if necessary) and see if you can find the error yourself. It has been many years since I had Special Relativity in an E&M class so I will not volunteer myself, but I have the utmost confidence in Mr. Kerr based on previous comments of his on other threads.
JimV: “Pentcho, Daniel does not know the details of your calculation per his last comment, so he can not tell you which of many possible errors you made.”
I shall return to the details of my calculation if necessary, but for the moment let us try something even simpler. Consider a light source emitting a series of pulses the distance between which is d. A stationary observer (receiver) measures the frequency of the pulses to be f = c/d:
http://www.einstein-online.info/images/spotlights/doppler/doppler_static.gif
The observer starts moving with speed v towards the light source – the measured frequency shifts from f = c/d to f’ = (c+v)/d (a shift confirmed experimentally and acceptable to both relativists and antirelativists):
http://www.einstein-online.info/images/spotlights/doppler/doppler_detector_blue.gif
Question: Why does the frequency shift from f = c/d to f’ = (c+v)/d ?
Answer 1 (fatal for Einstein’s relativity): Because the speed of the pulses relative to the observer shifts from c to c’ = c+v.
Answer 2 (possibly saving Einstein’s relativity): Because…
There is no reasonable statement that could become Answer 2.
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As I dimly understand it, c+v always comes out as c in Special Relativity, and the red-shift due to the universe’s expansion is caused by stretching of of the light-wave as the space it occupies expands, without changing its velocity. That’s without reading the article Daniel Kerr referenced, because it is probably too late for me to become well-versed in General Relativity if I wanted to, and I don’t particularly want to. I know that if I thought I had found a problem with Relativity which had eluded Einstein and all the good physicists since him, I would delve into GR long and hard before saying so publicly. Good luck with that.
Sorry, while I think that answer might be vaguely correct, it was not responsive to the scenario you proposed, and I think Dr. Volner, who taught my E&M course at Michigan State 50 years ago, would be disappointed in me, so I will try again.
Suppose there is a light source which you are moving toward at velocity v, which is timed to emit a light when you have reached a distance x0 from it, at time t0. The light reaches you at time t1, when you have traveled a distance v*(t1-t0), so you are then at distance x1=x0 -v*(t1-t0) from the light source. You will find, to within the limit of your experimental accuracy, that x1/(t1-t0) is equal to c (assuming the experiment takes place in a vacuum). This experiment has been replicated many times.
However, the frequency is determined by the rate of e-m fluctuation transverse to the direction of travel, so if you are counting peaks of that fluctuation versus time, they will come at you faster than they did in the reference frame of the source, so you will observe a higher frequency.
A notable difference between sound waves and light waves is that the pressure waves of sound move in the direction of travel, whereas the e-m waves of light move transverse to the direction of travel.
Your characterization of the evidence is subject to your own heavy bias. After investigating what has been done so far, the idea that it can all be accounted for by “error” and “coincidence” is very difficult to believe. Your “prior” probability is unjustifiable because you ignore the possibility of momentum conservation through novel phenomenon (such as quantum vacuum interaction, warping of space-time, or something else.) The theory in these areas is NOT sufficiently developed to justify your prior probability of zero. Not even close.
Prepare to be on the wrong side of history, sir.
@Daniel Kerr:
It’s not at all surprising that drunken individual particles take longer to get from A to B. 🙂
phayes,
Yes, that’s the role of geometry playing here. Even though the envelope has a straight path, it’s comprised of photons which are taking off axis paths. There should be a distribution of photons measured, some of which achieve c because they’re straight on path, and others which aren’t because they’re at an angle. This is entailed in the group velocity reduction, along each photon’s axis of propagation the photon must be moving at c. I really think this is a case of semantics since highlighting the group velocity, as they did in the paper, entails everything in that response, but it’s a good response for those who might be confused.
JimV,
Your explanation is perfectly adequate. The mistake Pentcho made was he assumed velocities add classically. Using the relativistic velocity transformation laws leads to the correct Doppler shift equations, which are provided in the wikipedia article I linked.
Daniel Kerr: “The mistake Pentcho made was he assumed velocities add classically. Using the relativistic velocity transformation laws leads to the correct Doppler shift equations”
1. I have made no such assumption.
2. If we argue over whether the speed of light is constant or variable, you cannot use “the relativistic velocity transformation laws”, for the simple reason that they are derived from the assumption that the speed of light is constant.
Pentcho,
Your answer 1 is “Because the speed of the pulses relative to the observer shifts from c to c’ = c+v.” This is the classical velocity addition. You can compare it to the relativistic velocity transformation, perform experiments and see which equation predicts the correct wavelength shifts. This has been done and it is the relativistic one. It doesn’t matter if c is constant or not, simply allow c to be a variable in the relativistic equations and it can handle a non-constant speed of light. As I said before, you have all of the means at your fingertips to understand this either through the wikipedia link or reading the appropriate physics textbook. Interacting with me will not lead you to accept the answer as you have presupposed that Einstein’s relativity should fail. I encourage you to approach this empirically but have realized for a number of comments now that my arguments cannot appeal to you since you continue to resist this approach.
Daniel Kerr: “Your answer 1 is “Because the speed of the pulses relative to the observer shifts from c to c’ = c+v.” This is the classical velocity addition.”
No. This is the variation of the speed of light (predicted by Newton’s emission theory of light) that explains why the frequency shifts from f = c/d to f’ = (c+v)/d.
This was an interesting paper that describes the theory behind it.
http://www.emdrive.com/theorypaper9-4.pdf
I had thought that drastically different frames of references could have direct implications on the other reference frame for a long time trying to resolve hidden variable issues, but I never thought it could have implications such as this. I would have a hard time getting my head around it. If it was an open system in one frame of reference, then the effects of that frame would have to carry over to the other frame of reference. Still not sure exactly how it could be considered an open frame of reference in another frame though, but if it was, it should carry over to being some kind of “weirdness” in each other frame.
Hello, this is for Dr. Carroll… Loved the lecture with wife on the black hole fire wall, she has sold some more books (me and family) … anyway… since this article is about fact v. fantasy, I want to run this by everyone…I ran across this. yourube of Professor Louis Gates who has appeared in numerous documentaries, and has always seemed to be a credible source of information, as has Neil DeGrasse-Tyson, but I ran across this and am unsure what to make of it… https://www.youtube.com/watch?v=GLvXaclRlHs Is the universe programmed by strings ? … and I always thought the Holographic principle was more of a metaphor not an actuality …how about some discussion on this?
@Pentcho Valev:
“Question: Why does the frequency shift from f = c/d to f’ = (c+v)/d ?
Answer 1 (fatal for Einstein’s relativity): Because the speed of the pulses relative to the observer shifts from c to c’ = c+v.
Answer 2 (possibly saving Einstein’s relativity): Because…”
Answer 2 is that the frequency, which is just the time between receiving successive peaks of the wave, changes because the source is at a different distance from you each time it emits a successive wave peak, so each successive peak has either a greater distance to travel to reach you than the previous peak (if the source is moving away from you) or a shorter distance to reach you than the previous peak (if the source is moving towards you). There is also a time dilation effect where the time between emission of peaks is slowed down in your frame, and this is why the relativistic Doppler shift equation is a bit different than the classical equation f’=(c+v)/d which you posted (see http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html for the correct relativistic equation). See my comment at http://physics.stackexchange.com/a/167871/59406 for a numerical example.
As stated by physicists such as the popular Brian Greene, all objects travel at the speed of light within the 4 dimensional environment known as Space-Time. This determines the limits. So much for warp speed. All that can be done is change the direction of that ongoing “c” motion. Thus if you were at rest in space, then you would be moving across the dimension of time with the same magnitude of motion of which light moves across space. If you then start moving across space, and do so via changing your direction of travel within Space-Time, time, for you, slows down.
Further analysis of this phenomena leads you to fully and independently understanding Special Relativity, and it also allows you to independently derive all of the SR equations, including the Lorentz transformation equations. No previous knowledge of physics is required to accomplish this. If you have say a grade 9 education, then you can achieve such an accomplishment. Go to 9 mini Youtube videos at http://goo.gl/fz4R0I to see this in action.
Yeah all this FTL and warp business is senseless media hype and click bait which muddied the waters. The fact still remains that multiple groups have reported thrust from conical resonant cavities, which should not happen…but it is. Folks should probably stop petting their sacred cows and hand waving about this, and go do some science instead. It isn’t like quantum anomalies are anything new. There’s also plenty of research published about Casimir momentum too.
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Jere…Miah,
These are your comments so far:
“”Wow this blog post really bombed hard. You might as well have pasted “dadgummit!” five hundred times.
Read the reaction…
https://www.reddit.com/r/EmDrive/comments/37j42n/sean_carol_critique_warp_drives_and_scientific/“”
“”Sure would be nice if some of you smart people would come over to the EmDrive developments thread where all this hoopla began and help out. Lots of math and science happening there. We’re trying to figure this thing out!
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1382971#msg1382971“”
“”Yeah all this FTL and warp business is senseless media hype and click bait which muddied the waters. The fact still remains that multiple groups have reported thrust from conical resonant cavities, which should not happen…but it is. Folks should probably stop petting their sacred cows and hand waving about this, and go do some science instead. It isn’t like quantum anomalies are anything new. There’s also plenty of research published about Casimir momentum too.””
What do you think that we think about you when you talk like that? Why is this a personal crusade for you and people like you? I don’t understand your hostility. The evidence that you think you have isn’t evidence, it’s hearsay and rumors amongst people who don’t produce science or technology or viable theoretical work. When we say evidence, we mean proof that another person can read. When we say published; Arxiv is a free site that almost anyone can publish to. viXra is another free one for the less reasonable claims. So if there isn’t anything published, then it means that they really have nothing or that they just don’t care. Joe Rogan (comedian and UFC announcer) has a series of videos; they start out with him 100% denying the moon landing stating hard scientific evidence which proves beyond a shadow of a doubt that the moon landing was faked. Then 3 videos later he’s doing an interview about it with Neil Degrasse Tyson admitting that he was a complete moron(he actually calls himself a “stupid asshole”), not because he thought that the moon landing was fake, but because he bought all the lies based on false science, basically claiming that science doesn’t support a moon landing; when it actually does! Never mind the people who went there and building sized spaceships. There comes a point when we take things too personally and we make fools of ourselves for doing it. I know a guy who spends his retirement hunting for “sasquatches” in Alaska. He was a mechanical engineer. Most knowledgeable people are intelligent too, but a hefty chunk aren’t. There are plenty of stupid, yet knowledgeable people. What’s frightening is how many people don’t know that and end up attacking the intelligent and knowledgeable people who know beyond doubt what they’re talking about. Just like the moon landings (plural).
Eppur si muove.
It’s like the science version of ISIS.
Dear sean to your answer about stardrive engineering saucer project that we done for bid for Nasa.gov contract was 10 warp dimensional drive saucers ! the first saucer of 10 built in oct 20,1989 to march 1992 finish and tested !the saucer is 100 feet around in diameter or 33 yard in diameter and height 7 feet high and propulsion systems is Electromagnetic with 4 warp dimensional coils with Electron ring that spin up to 100K R.P.M. to create a Electromagnetic fields around the outside of the saucer to hover to go forward and backward and upward and downward by using computer servos connected to second computer that made warp dimensional drive adjustments for speed ! the first computer made all the navigational mathematical calculation from the star charts that nasa give stardrive engineer! first we are talking about (warp dimensional drive systems)in Quantum mechanics physics ( this based on scientific factual data from science physicists from Faraday and Maxwell and Nickola Tesla in Electromagnetic fields ! mark tomion is Master Electrical Engineer in Quantum Mechanics and Author of stardrive engineering manual book from stardrive saucer technical builter manual book for nasa ! mark tomion published in American Electrical
assoication and Advanced scientific Research in year 2000! please understand their not be rude but their whole bIg Differant world when it
come to advanced Engineering in reality in every day life and than to theoretical physics on a chalk board ! i ve been advanced machinery Designer and builder for robotics systems and computer programmer for 20 years in advanced engineering dept with mark tomion master Electrical Engineer in Quantum physics in the early 1970s and 1980s at kodak than we left their ! sean iam given the scientific information for the stardrive engineering mark tomion ! iam professional Designer and Advanced machinery Builter and computer programmer and well respected in my field for 20 year plus ! if have and question or you dont know something on scientific research on stardrive engineer in science questions contact me ! alexander swage quote by winston churchhill (everything is possible and possiblity are endless)
alexander swage a.swage@gmail.com
Pentcho: I think the problem in your reasoning is that you are using velocity=distance/time… the formula for velocity in a relativistic scenario is different
@Pepe – That’s not true, for an object moving at constant velocity in a single inertial frame, its coordinate velocity in that frame is still equal to coordinate distance divided by coordinate time. It’s only when you want to compare readings in multiple different frames, as with the velocity addition formula, that you can no longer rely on Newtonian assumptions about velocity. See my comment of June 6 2015 at 11:30 am for what I think Pentcho is confused about.