The scientific instruments on uncrewed space probes have revealed many amazing things about the universe. But there is a possibility that simply monitoring their trajectories across the solar system may reveal something more fundamental than anything they have been actually intended to investigate.
Historically, tracking the motions of celestial objects has provoked several revolutions in physics and cosmology. Tycho Brahe’s observations of the planets led to Johannes Kepler’s “laws of planetary motion”, which soon after led to Isaac Newton’s theory of gravitation, which predicts the motion of the planets to enormously high accuracy. But as the accuracy of observations improved, there was another tiny discrepancy discovered - Mercury’s orbit didn’t quite match the predictions of Newton’s laws. When Einstein’s theory of general relativity was published in 1915, the fact that its theoretical predictions exactly matched the observed behaviour of Mercury was a convincing argument in its favour.
But a number of uncrewed spacecraft have, over the past few years, done some things that can’t easily be explained by conventional physics.
The first anomaly was observed in the track of the first outer solar system probes, Pioneer 10 and 11. As this article explains, these probes have wandered ever-so-slightly off course from where the laws of physics would suggest that they should go. The prosaic explanation is that there is something on the craft themselves - perhaps the heat from the spacecraft’s radioactive heaters - which is pushing the spacecraft off course. But there’s two other possibilities - either there is some other force acting on the craft that we don’t know about, or that Einstein’s general theory is, in some incredibly subtle way, “wrong” - that is, gravity actually works in some slightly different way to what GR says.
While scientists puzzle over the Pioneer anomalies, a second group of spacecraft motion anomalies have been discovered. Because of the vagaries of propelling things around our large solar system with our puny chemical rockets (don’t get me started on the better alternatives…) sometimes space probes do “Earth flyby” maneuvers to get where they are going efficiently. In an Earth flyby, the probe, after leaving earth and whizzing around in deep space, comes back past to travel towards its ultimate destination. Such gravity assists can speed up space missions substantially. However, something strange was being noticed during Earth flybys. They were actually speeding up the spacecraft ever-so-slightly more than what was expected. Again, the effect was small, but the standard explanations - something radiating from the spacecraft, such as escaping gas - couldn’t account for it.
However, some clever people have now developed a mathematical model that, while not explaining the phenomenon of the Earth flyby anomalies, quantifies it. According to this New Scientist article, the amount of anomaly relates to the angles of the spacecraft’s path compared to the Earth’s equator, indicating that the Earth’s rotation is somehow involved.
It’s interesting to compare the situation to that of Newtonian mechanics, so long ago. Observations, like Brahe, have now been used to develop a mathematical model that predicts the specific behaviour observed - like Kepler. Assuming that the model holds up to further observation, we now wait for our Newton to come along and turn the model into a more general theory about what’s actually going on.
Of course, the odds are that this anomaly - and the Pioneer anomaly - will eventually be explained in a way that doesn’t involve revising general relativity. But it’s just possible that the routine transits of space probes may teach us something far more profound than the scientific instruments that they were actually built to carry. And that’s the humbling, but profoundly fascinating, thing about science. You never know when you’re going to stumble onto something big.
Interesting Robert!
So we’d have to assume they’ve already taken into account the gentle zephyr breezes of the solar wind, unmapped until the 1960s, 1970s; or an anomalusly larger-than-supposed amount of orbiting dust out past Pluto?
If it’s a rotation-of-mass effect, then we’d see it at Jupiter (much larger mass than Earth), and more strongly at the Sun, wouldn’t we? The Sun’s mass is very large and its rotational period’s about 30 days isn’t it? Or are the radiation forces and solar wind forces too large and variable near the Sun to separate out this new anomaly?
Hey! Let’s do some theoretical physics on LP.
Can I start with some pointless abuse? “Einstein was a bloody smartarse, fled to the USA, supporter of Israel, bloody pacifist!” C’mon bloggers…
Robert, Endlessly fascinating stuff. I was also struck by your comment:
Of course, Newton himself insisted his own mathematical model quantifying the laws of gravity and motion did not explain the phenomena, either.
Hypotheses non fingo.
Read the other day somewhere of an exploding nova likely to hit or destroy Earth in several millenium. Wonder if the energy waves from that, 8 million light years ago, I gather, might be having some sort of subtle effect. My knowledge on these sort of things is the GP sort.
Ambigulous: I think it’s safe to assume they’ve taken the solar wind into consideration. Dust is a possibility, I suppose, but, again, that would have been one of the first things I’d check; in any case, I think they have some kind of dust sensor on the Pioneer probes.
I should make clear I’m not a physicist, just a lowly software engineering type whose physics ran out in first-year uni.
As far as the flyby anomaly goes, I would guess that it’s much easier to measure the flyby anomaly with Earth flybys than solar or Jupiter flybys - in any case, there’s a lot more of those. But it would be an obvious thing to check.
Paul: a supernova that distant is highly unlikely to be a risk to us; in any case, any radiation pressure from it would be directional, would vary over time, and would be estimable from Earth. None of these factors seem to apply to the Pioneer anomaly, nor the flyby anomalies.
Maybe the Big Fella’s playing dice.
There is Modified Newtonian Dynamics as an alternative.
nice topic Robert, i like these reminders that we haven’t wrapped up all the math, esp in areas that my schoolboy sf assurred me that it was all done and dusted.
my first thought re the pioneer anomolies was the kuiper belt and ort clouds, there is a large amount of mass there that has not been mapped and its graitational effect is at the moment unknowable. my other thought regarded sol’s bowshock and wake, i can never remember which pioneer is going where. my limited understanding of the bow shock, where sol’s ‘wind’ meets the galactic ‘calm’, is that it is probably an area of relatively high energy, again with uncharted effects.
of course neither of these options would explain the near earth flyby annomolies and appart from some musings re earths dynamic magnetic field and a general distrust of all those smooth curves which seem to populate graphic illustrations of gravity wells and the like, i got nothing.
i’d like to accept ambigulous’ challenge and i pointlessly abuse lord cherwell, churchill’s science advisor, as a small minded man more concerned with his reputation and pet projects than the protection of britain.
I wonder if:
* they’ll run future probes through gravity assists around other bodies in the solar system specifically looking for their behaviour to correspond with this new model’s predictions
* Gravity Probe B will pick up this effect
I’d like to pointedly abuse John Howard for his insult to the nation and planet, in his corrupt appointment of the coal industry lackey, Robin Batterham, as our supposed chief scientist, and then only in a part time capacity, as if real science and research mattered so little.
They self-servingly starved our renewable energy industries and researchers of funds, wasted crucial time and talent that could have been devoted to the challenge of sustainable living on the planet.
Thanks to them, Australia is now just a bigger part of the problem, when it could have been a big part of the solution.
A pox on both their houses.
Eliot: “explain” is of course a problematic term. At some level, there is no “why” - it just is - and going further is philosophy, not science.
“Generalize so that the concepts are universal, or widely appliable, rather than ad-hoc to the particular situation” is a more accurate description of the process.
This reminds me of a book I read about the state of science at the start of the twentieth century - it was believed that the science was largely settled with only a few troubling loose ends to wrap up. Those “loose ends” led to the Theory of Relativity and, more importantly, quantum physics which destroyed the relatively cosy world that existed prior to their discovery.
I get the feeling the same thing is in progress here.
Thanks Robert,
good one dylwah - yep, let’s see if we can divert this thread onto a severe and un-nuanced critique of Bad Lord Cherwell, shall we?
Nah, I’d rather talk about the physics. As you no doubt guessed, I was making fun of the bloggers who get stuck into a meaty topic, and then start hurling abuse (pointlessly?) - either at a pet hate or at a fellow blogperson.
Robert, aren’t there well-established models in General Relativity for the gravitational field surrounding a spinning mass? I would’ve thought so. If a black hole can be formed by a collapsing star, and many stars spin, you’d wanna model that case, si?
Anyway, it’s a good topic this one: something that keeps science interesting even in a field where things seem settled and fully understood - some clown comes along with anomalous data….
I believe so, but, again, this is not an area which I claim to understand at anything beyond a pop-science level.
Clearly, at some point I should get a GR textbook and have a look through it.
Andrew Reynolds, you are probably thinking of Lord Kelvin’s statement, “There is nothing new to be discovered in physics now; all that remains is more and more precise measurement.” Looks like our precise measurement is getting us somewhere, anyway.
I’m putting in a vote for a Dark Matter Effect. Or possibly the Cetagandans at work.
As I understand it there are actually several alternatives to General Relativity already out there. On all the tests we have been able to devise they produce identical results to GR, and GR is much more elegant, so we use it. However, there are cases where the alternatives would produce different results, its just that either to distinguish would require precision in measurements we have not yet been able to achieve, or experiments on a scale which is beyond us.
I don’t know if the results from these probes could be useful in testing the difference between these theories.
What about small black holes that appear and disappear at random? Stephen Hawking started to theorise about some of these things in the universe and what effect they might have on stuff.
Great post! Love it!
Could it be anything to do with metal spacecraft passing at great speed through the planet’s magnetic field? It talks about the angle of incidence and departure to the equator playing a large role, doesn’t that also imply there’s a correlation in the variance with the N-S field lines?
I’m trying to remember my year 12 physics and the thing with the right hand rule, but my teacher was an american vietnam vet / ex-aircraft technician who just liked to give the class electric shocks. This was pretty funny at the time but I don’t remember much of the material…
Great post Robert!
According to one of the articles Robert linked to the guys studying this did take this into account, apparently this effect doesn’t describe the anomalies.
There’s a tendency in most physical theories to assume that everything is “a sphere in the vacuum” till proven otherwise. Then it’s always question of working out how to make a sphere in a vacuum look, mathematically, like something real. It’s what most physicists spend most their time doing!
So, my personal biases tell me that the answer to this problem will turn out to be something simple that has been overlooked and not something that will revolutionize physics. Normally you have to do these calculations by crunching data on computers and the big debates are normally which simplifications are the right ones to make.
mick: “There’s a tendency… to assume that everything is “a sphere in the vacuumâ€? till proven otherwise. Then it’s always question of working out how to make a sphere in a vacuum look, mathematically, like something real…
So, my personal biases tell me that the answer to this problem will turn out to be something simple that has been overlooked and not something that will revolutionize physics.”
This sort of thing always makes me wonder if simple will might be a hidden factor. The spacecraft are not random inert objects like meteors, they were made by us and they have their own (presumably variable) propulsion. And they were willed into being, by us. Maybe that makes them slightly different somehow from a rock or a ’sphere in the vacuum’. After all, will is an actual factor in the physical world, (witness us, among many other examples) though it seems to have no detectable physical presence. I wonder, say, what the physics calculations look like for a dolphin or another huge marine animal leaping out of the water: maybe there’s a slight extra effect there, that can’t be accounted for by just the simple mass and gravity figures: maybe the creature’s will to leap has something to do with it. There’s the famous example of the bumblebee in flight. Could be the same here in an odd way.
This should make the people involved with quantium physics excited - something new they can apply their new theories involving multiple dimensions that are all interlinked and how gravity could originate from a dimension far from ours.
For example the earth being as large a mass as it is may have an effect on ‘time’. This may be causing some kind of momentum like a ball down a gentle slope. The observation would that craft are travelling faster when in fact they’re moving forward in time. We already know that satellites and shuttles in orbit go forward in time ever so slightly due to their speed so the possibility exists.
I’m not a scientist. I just like to read and watch such things while trying to understand.
j_p_z - I think maybe you are over-thinking this. What I meant was something more like our estimates of the effect of the mass of Pluto or something is different than we thought because we don’t know the mass of Pluto well enough (not that I’m suggesting that this is the case, it’s just an example).
But, you do strike an interesting point. Physics does tend to take a “bottom-up” approach to science. We try to understand the simple cases first and then build our models of what really happens out of the simple models. It may very well be the case that this approach isn’t always satisfactory.
A great example is the physical phenomena of Bose Einstein Condensation (BEC). BEC is a phase of matter and as such only occurs as a result of the collective behaviour of many particles at once. If you didn’t know something about the way particles behave en masse then a bottom-up approach to science wouldn’t let you predict this phenomena (without a lot of lucky guess work that is).
Actually, my first forays into numerical physics was studying some new BEC experiments that people were struggling to explain. I was actually thinking about this stuff when writing the above comment! I remember that the experiment that we were analyzing didn’t really fit the existing theory, so we were searching for physical effects that might give us the right numbers. Basically, we took the existing theory and started adding extra features (carefully that is, not just randomly throwing equations about) to it in order to try to make it match the number that the experimentalists were emailing us! I gather this is prety much what the team that Robert’s article is about were doing as well.
If I were a physics crackpot I’d say that this problem just shows that modern physics is a hoax and should be abandoned by any intelligent person. You’ll all need to let loose your allegiance to that huckster Einstein and become one with the electric universe.
But I’m not and will be content with a fascinating post Robert.
I cannot add much that is intelligent in the sense of the phenomena pointed out.Accept a rather blinding observation about points and pointedly.I think mathematics for the simple folk here will screw up badly,if we dared,not notice we aint out there when this stuff happens,we cannot even breathe on the phenomena.Or mathematical contrivances as a human product have noticed only recently the edges of things are not so cut and dried as the mind and eyes or the minds eye sees..thus chaos theory and even remapping of countries ocean and geological boundaries.This stuff is in the realm of the boundary layer phenomena again.Solar effusion radiation or a another proof in making,of Wal Thornhill s contentions.Back to biting my bum,cannot even solve my life s jigsaw at present!
It’s on threads like these that I begin to miss Birdy.
mister z,
your physics teacher would have wanted you to know that an electric charge moving across a magnetic field experiences a force, and yes: right hand rule is the go. But I think it’s unlikely that these spacecraft carry much charge. Especiaaly near Earth where the freely moving charged particles in the solar wind would soon neutralise the charge on the spacecraft.
Solar wind particles get so deflected by the magnetic field of Earth, many get trapped in the field. Then in a magnetic storm, some spill down into the upper atmosphere: auroras!
Ah, I love the smell of plasma physics in the morning! Great post, Robert.
Obviously at the equator the forces acting on the oceans are at a maximum, ie centripetal forces which causes a ripple in the gravity waves emanating from the earth.
This is being worked on as we speak, development of the Grand Unified Theory…
Of Wettness
Where’s Jack? Birdy can’t explain it.
mick: “I think maybe you are over-thinking this.”
Well that’s *far* too polite! I’m not really even ‘thinking’ here, just engaging in wacky non-scientific speculation. But why not? My underlying point is just an ongoing conviction that the universe, even the ’scientifically explicable’ part, is probably much, much weirder in ‘reality’ than even our most cutting-edge theoreticians imagine it to be. The sense in which any (or all) scientific theory is not actually literally “true” but simply a collection of our best, most convincing and most elegant guesses up to and including a moment ago, is a thing we ought to recall from time to time. Meanwhile though, whatever reality actually ‘is’ so to speak, remains that way independently of what we think we ‘know’ about it. Maybe.
“We like the world because we do.”
– Stevens
Ambigulous “I was making fun of the bloggers who get stuck into a meaty topic, and then start hurling abuse (pointlessly?) - either at a pet hate or at a fellow blogperson.”
Pet hates safely ensconsed at the boarding kennel.
Robert is the flyby anomolly apparent in the trajectory etc of near earth meteors, or is it only our objects that are affected?
Dylwah, that’s a good question. I don’t know.
However, I’d guess that the trajectories of your typical near-earth meteor may not be tracked to the precision necessary to detect the perturbation, and in any case are likely to be rather different than the space probes concerned.
Very good points dylwah & Robert
I think a major advantage we’d have in tracvking “our” objects is they’d be sending regular (continuous?) radio signals, so you could measure subtle Doeppler effects and get distance measurements MUCH more accurately than for the [larger] space rocks - largeness implying some extra uncertainty in defining position = location of centre of mass
j_p_z : you’re right, science is a set of our latest, best, most convincing, most elegant guesses: but what a magnificent set they are even now, in the infancy of science… maaaate !!
Robert,
Thank you for taking the time to blog on this subject. Spent a pleasant hour reading about this big science project.
Cannot comment on a reason that the pioneer’s have slowed, but I do love the understated understanding that we still do not know it all.
Makes you wonder if “She” has bequothed this to us for a purpose ?!?
mick,
If you want a dose of GMB on this topic, catallaxy has one going which started as a discussion on the Hayek Essay Competition and went to Einstein’s theory in the very first comment. Must be a new record of some description.