“A thing may be of deeper impossibility than another, in the sense that you can be more deeply underwater–but whether you are five feet or five fathoms from the surface you are still all wet.” -Brian McGreevy
It’s been a spectacular week of investigating the Universe and our knowledge about it here at Starts With A Bang! There were a great many of you wondering about parallel Universes over the past month, and that’s exactly — in the context of quantum physics and cosmic inflation — what this past month’s Starts With A Bang podcast was on. Check it out!
- Why must time be a dimension? (for Ask Ethan),
- How the first false alien signal opened up a new world in astronomy (for Mostly Mute Monday),
- Cosmic rays may reveal new particles just out of LHC’s reach (a great contribution from Sabine Hossenfelder),
- Could dark matter be powering the EMdrive?,
- What to watch for when science becomes politicized, and
- LHC’s newest data: victory for the Standard Model, defeat for new physics.
The video ads are gone from Forbes, but if you still prefer your Starts With A Bang ad-free, you can catch everything on a one-week delay over on Medium for free, thanks to our Patreon supporters. With all that said, let’s take a look at what you’ve had to say in our comments of the week!
From MobiusKlein on Pluto’s subsurface ocean: “Regarding the 250K limit on H2O as a liquid – does that apply to impure water as well? Or do we suspect the impurities in icy dwarf planets to be slight enough to not matter?”
It’s well-known that increasing the pressure on solid ice can transform it into liquid water, but there are limits to this. No matter how much pressure you apply, if your temperature is below about 250 K (about -23º C or about -10º F), it will only transition into different ice states, not into a liquid state. But the reason for this is that for pure water molecules, arrangement into a particular lattice is more energetically favorable at these pressures and temperatures. In fact, at high enough pressures, it’s always solid.
But this is only for pure H2O. Add in impurities of any variety — create a mixture or a solution — and lower-temperature liquids are possible. This is what happens on Mars, where the solid/liquid/vapor triple point is lowered in pressure space, enabling the existence of liquid brine where only solid or gaseous pure water is otherwise possible. Whether that ocean is briny or not has not yet been determined, but the evidence strongly suggests a liquid subsurface ocean on Pluto. This hasn’t been studied particularly well at high pressures, but low-pressure behavior indicates that the freezing point should be lowered at higher pressures, too. Quantitatively, I’m not sure by how much.
From Tristram on the location of Starts With A Bang: “Nay, a link to forbes, still.”
Alas, ’tis true. But the autoplaying videos are gone, plus the newly released Chrome 55 allows you to block/disable autoplaying content not only through flash but through html5 as well. What a world we live in. Give it a try; it might not disappoint you.
From Wes on a tongue-in-cheek interpretation of dimensions: “I still think we observe π dimensions.”
The marginal evidence for variation in the fine-structure constant is still observed by looking at very distant absorption features. Although there are systematic and astrophysical explanations for the shift in the deuterium features, and hence inferred for that constant, it is also conceivable that some fundamental value is changing. Maybe it’s e, the electron charge; maybe it’s c, the speed of light, or maybe it’s h, Planck’s constant. Some people (jokingly) argue that it’s either 4 or π that change, but those are (thankfully) jokes. I am betting that this was, too, although I’ll point out that in sufficiently curved space, the ratio of a circle’s diameter to its circumference is no longer π at all!
From Frank on relativity and time’s dimensionality: “Bending of space-time is well established fact in astronomy. Which I think is the biggest proof that time is a dimension, just like dimensions of space.”
There’s actually a bigger proof from relativity: the Shapiro time-delay. One of the coolest things that relativity predicts is not simply that spatial paths get bent due to the curvature of space, but that the amount of time they take to traverse them — including climbing out of or falling into a gravitational well — is intricately affected by spacetime’s curvature. This is known, sometimes, as the “fourth classical test” of relativity, even though it was only performed after Einstein’s death. Many of his greatest theory’s greatest victories have continue to come nearly two full generations after the man himself has passed on.
From Omega Centauri on spinning neutron stars: “Thinking about the orientation of the magnetic field, one would guess that based upon symmetry alone,that the favored orientation of the dipole field would be along the spin axis. Presumably if we were able to measure a large unbiased sample of NS, and measure the angle between the spin axis, and the magnetic pole we would get a distribution. I’m guessing it is fairly strongly peaked around zero degrees.”
We can’t really measure anything other than the magnetic axis of the neutron star (as Michael alluded to), since it’s the magnetic field of the neutron star that causes particles to accelerate and hence, for the “pulsing” behavior to occur. What we see is that the magnetic axis spins around, and when the “beam” from the poles passes Earth, we see that pulse. But if all we had were the axis pointing at us, we’d see it all the time, like a mini-blazar. Instead, it pulses, and that tells us this is what’s going on:
From Michael Kelsey on a fun calculation of the axion/DM possibility: “It seems like this speculation hinges on quantitative questions: What is the local axion DM density? What is the axion-photon scattering cross-section (as opposed to photon-axion mixing)? What is the photon density in the EMDrive cavity?
I can very roughly estimate the latter. The average density of dark matter is about 5 GeV/cm^3 (don’t you love mixing units!), based on the very approximate ISM density of 1 hydrogen atom per cm^3, and DM being five times normal matter. The axion mass is estimated at a fraction of an meV (“milli” not “mega”). So the number density in the EM drive (and everywhere else) is something times 10^12/cm^3.
That’s surprisingly non-negligible, actually. If those were regular atoms, they would be at a pressure of microbars or less, which is typical of high vacuum systems, but not super extreme.
The cross-section is more problematic. A 2014 paper (https://arxiv.org/abs/1402.4937) calculates cross-sections around 10^-29 cm^2 (10^-2 mb) for typical interactions, but enhanced up to 10^-17 cm^2 (10 Mb !!) in a resonant cavity. I don’t do axion physics, so I don’t have a really good sense for how realistic this might be, but let’s proceed…
If the EM drive is the perfect magical cavity for axion-photon interaction, then we can combine the density and cross-section to say that photons would have a mean free path around 10^5 cm (1 km), so we might expect 1 in 1000 photons in a 1 m cavity to interact with an axion.
The figure above says they put 100 W of power into the cavity. A conversion rate of 1e-3 would mean something like 0.1 W of “disappearing” power, which would be immediately noticeable, I think.”
But this actually, lines up perfectly with what we need! What they observed was approximately one micronewton of thrust (Force) for every one Watt (energy) of input power. See for yourself:
Now, if we want to convert energy into momentum, the key is to kick back a massive thing; momentum is related to energy, and a change in momentum over time is what gives you a force. So if you can kick axions out — preferentially in one direction, which is conceivable with a strong, directional electromagnetic field inside — in the backwards direction, you can create thrust in the forwards direction.
It’s a very, very speculative (but fun) possibility. Of course, by far the more likely explanation is that conventional physics holds, this isn’t dark matter, and rather this is a clever setup with no net force produced. More than three data points would be helpful, and reproducible results with much smaller measurement errors (look at that 60W point and how the individual measurements range by a factor of three in their results!) would be much more compelling.
From Julian Frost on politicized science: “Two of the things you mentioned (AIDS and vaccines) have a place in my heart.
As an autistic self advocate and blogger, the persistence of the lie about vaccines causing autism is both infuriating and frustrating. Andrew Wakefield, the struck off gastroenterologist who kicked things off has been exposed as having taken money from lawyers to investigate the link to see if lawsuits could be brought. In addition, even though he loaded the deck as hard as he could, the results didn’t fit the claim, so he cooked the subject’s data. Huge epidemiological studies have failed to find a link, yet there are still those who are convinced that vaccines cause autism.
I’m a South African. Thabo Mbeki, our President from 1999-2008, when he was forced to resign, had views on AIDS that could politely be called eccentric, and accurately called absurd. His beliefs meant that ARV’s were denied to patients. One estimate puts the death toll from his actions at 365,000. It’s a shocking example of how ignoring the science for a belief in conspiracies leads to disaster.”
There are people in my life who had AIDS in the 1990s… and many of them are either dead now or destitute and in poor but stable health. There is a common “logical fallacy” out there called appeal to authority, but most people misinterpret it and use it in an indefensible manner.
They will point to a climate expert and say, “don’t take this person’s word for it; that’s an appeal to authority.” Or a series of dental health experts on fluoride, or the CDC on vaccines. Or an astrophysicist on astrophysics, or a particle physicist on particle physics. “Figure it out for yourself, like a good rugged individualist.”
Shame on you for your twisting of what the “appeal to authority” fallacy was all about. It’s not about decrying looking to a qualified expert for an expert opinion. It’s why your surgeon knows better than you about your surgery; your car mechanic knows better than you about your car; your electrician knows better than you about how your home is wired; your friendly neighborhood astrophysicist knows more about astrophysics. But they also know more than your church, your legislator or congressperson, your president or your spouse or parent. Or even than “Age Of Autism,” “Erin Brockovich” or the “Fluoride Action Network.”
It’s because that logical fallacy is telling you don’t listen to an appeal to a false authority. A bona fide expert with expert training, expert knowledge and expert judgment isn’t hard to find, but you have to look. And you have to demand expertise. If you listen to the Food Babe or Mike Adams or Joe Mercola or Doctor Oz, you deserve it. If you let them make policy for your nation or your world and you don’t fight it, you deserve it.
I’m not going anywhere, and I’m not going to be one of the silent ones who lets our world slip into ignorance. I cannot promise we’ll win this war, but we’re not going down without a fight.
From CFT on demonstrating this problem exactly: “Ethan, You are a coward. […] Want to prove me wrong? Prove you know their arguments, then be able to show why they are wrong, like any half assed science teacher worth their diploma would do.”
This is not what I choose to blog about. Either learn the real science from real scientists and real experts, or draw your own false conclusions from your own false sources and false information. But I feel no compulsion to do your bidding. Dig your own grave if you like, but I refuse to be dragged into it.
From Eric Habegger on the same topic: “I have similar concerns as you. A lot of knowledge that used to be passed by authority figures from generation to generation has very recently been bypassed by the hive mind of the internet, and global instant communication. It has been very disruptive in a way that is both surprising and counterintuitive. A lot of it has to do with the anonymity of authors in messaging. In real life we can identify unreliable memes in culture just by the image and reputation of the speaker. Now that isn’t possible and the “feelings” of the individual reading it bypasses the logical responses because those individuals do not realize they are getting incomplete, or false information. Let’s face it, many people just do not have the critical thinking ability to weigh the probability of something being true or false in the presence of many diverging opinions coming at them AND not having the additional information on the character of the person saying those things that we used to have.”
And many people don’t care what the facts are; they care about justifying the original position they staked out. They will tell whatever lies or untruths are necessary to justify the actions they want to execute. And they don’t care if they need to cherry pick or even fabricate facts to sell their overall conclusion; they have an agenda. It is everyone’s job — scientists, the press, and ordinary citizens (and non-citizens) — to make the truth matter. Right and wrong shouldn’t always be up for debate. We don’t vote on the sky color, and voting on it doesn’t change it. Perhaps we have a right to be free from misinformation masquerading as truths, too.
From bert hubert on the ‘science is over’ quote from Kelvin: “While a great quote, it is not from Kelvin but from Albert A. Michelson. See https://en.wikiquote.org/wiki/William_Thomson#Misattributed“
Perhaps it’s time to retire that misquote forever, since neither Kelvin nor Michelson ever intended it to be used with the meaning it’s often attributed. Thanks for the education.
From Anonymous Coward on the LHC’s failure to turn up anything new: “So we’ve reached the Desert. No new physics from 10^12 eV to 10^25 eV (the grand unification scale), and that’s a long, long way away. No way we’re bridging that gap even if we could build an accelerator that circles the planet.”
It means that colliders aren’t the answer. It means the LHC won’t reveal new physics, and that particle creation, decays and branching ratios won’t shed the light we need them to at reachable energies. But there are always indirect methods to probe new physics. We will have to rely more heavily on those. Indeed, that’s what’s given us our beyond-the-standard-model hints: B and S-factories for CP-violation; neutrino measurements for masses and oscillations; cosmic ray experiments for beyond-collider energies. There is hope, but it doesn’t look like building a giant collider.
And finally, from Eboy on our knowledge: “Until you solve the mystery of gravity particles or ?, you really have figured out anything.”
Nonsense. Our theory of gravitation works just fine for every regime we’ve been able to test it in, and we have a long way to go before trans-GR physics shows up. The idea that “you don’t know everything and therefore you don’t know anything” is the perhaps worst solipsistic argument I’ve ever encountered. We have a long way to go and always will, but that doesn’t mean the Sun won’t rise in the east tomorrow.
Have a great week ahead, everyone, and looking forward to all the science we’ll continue to share!