[T]he weirder thing is what happens if I have two traps, separated from one another, and I put the electron in one trap. Yes, the center of either trap is a good stable location for the electron. That’s still true… in the sense that the electron can stay there and won’t run away if you jiggle the trap.
However, if I put the electron in trap number 1, and walk away, sealing the room etc., there’s a certain probability (Figure 4) that when I come back the electron will be in trap number 2.
Archive for April, 2014
Let’s break up into teams. Inertial frames on the right, non-inertial frames on the left…
[T]his weekend I enlisted SteelyKid’s help to make a video illustrating a different sort of physics with the merry-go-round, a camera, and a tennis ball
The science should be round and firm, not mushy. Thump it, and you should get a solid feeling. It should not ring hollow.
Slightly biased toward life sciences results, but a pretty good guide.
Why does the balloon move forward when the van accelerates [forward], while the plumb bob swings backward?
[I]t turns out that all objects are light emitters. It just happens that the light emitted from most objects is not visible to the human eye.
[O]ther things apart from gravitational waves, such as dust, can emit polarised photons.
To minimise the chances of this effect causing a false signal, the BICEP 2 team pointed their telescope at a patch of sky far away from the Milky Way’s dusty disc. Then they used models of the dust in that part of the sky to estimate its effect on the polarisation. They found that this could account for no more than about 20 per cent of the signal that they attributed to gravitational waves last month.
But Mertsch says the models they used didn’t account for dust shells produced as the expanding remnants of supernovae slam into surrounding gas and dust.
So the results may not hold up. This is bad, right? We get all worked up about a result, and it turns out it might not be correct.
Except it’s not. Procedurally, this is good. This is exactly the way science is supposed to work. You do your best attempt at the research and looking for confounding effects that might be giving you a false signal. You have it peer reviewed, and you publish. As I’ve talked about before, that’s just the first hurdle. After that comes feedback from other scientists, including attempts at replication. And that’s where we are now — some attempts at replication are already ongoing, and here we have someone who has new information that might affect the conclusion. This is how science moves to get things right.
The bad part is that the first results get hyped, because they’re new, and there’s no restraint for waiting for the weight of evidence to pile up. Sometimes the first results won’t stand up to scrutiny. I recognize that this might weaken the confidence some have in science, but in reality it should strengthen it: other scientists are willing (enthusiastic, even) to stand up and say, “Wait a minute!” when all the ducks don’t line up. There’s no conspiracy to conform. Scientists questioning loudly trumpeted results like this gives me confidence that all of science is subject to the same kind of feedback.
Magnetically actuated micro-robots for advanced manipulation applications.
In rod we trust.
I don’t spend much effort thinking about this sort of issue, since I’m much more interested in the experimental aspects of measuring time than the philosophical aspects of it, but I’ve run across some folks who think this problem of “Now” is so perplexing they can’t get past it. (again, because my interests lie elsewhere, this seems more of a dorm-room discussion, or possibly one involving a professor who looks like Donald Sutherland discussing whether atoms can be universes). My view of the utility of this is that while “It’s always now” may or may not be deep thinking, it doesn’t help GPS tell you where you are. (unless “You are here” is an acceptable answer)
[R]egardless of whether you use an external definition of time (some coordinate system) or an internal definition (such as the length of the curve), every single instant on that curve is just some point in space-time. Which one, then, is “now”?
Later on there’s also an interesting point about memory not needing consciousness.
Researchers put plastic backpacks on cows, then inserted tubes into their rumens (their biggest digestive tract). They extracted the methane–about 300 liters a day. That’s enough to run a car, or a fridge for 24 hours.
[T]his equating of “physics” with “particle physics” not only plays along with the media myth that the only thing worth noting in physics is what is going on at CERN, but also explains outbursts like this one I received from a (non-particle) physicist recently: “Perhaps the poster child for overselling science should be high-energy physics. They oversold the most expensive toys that physicists have ever produced: high-energy particle accelerators… their arrogance when they talk about ‘the god particle’ and ‘the most important problems’ is disappointing.”