Science questions not worth a thread I: I'm a moron!

[Zkribbler]

I loved those helicopter-saucers in The Incredibles. I really wanted one until I realized that, while the hoverblade was rotating clockwise, Newton's 3rd Law would cause the cabin to rotate counter clockwise.

 

[Gigaz]

They might have two hoverblades, one rotating clockwise and one counter clockwise.

 

[Birdjaguar]

Have any of you read Life on the Edge by McFadden & Al-Khalili? It is about quantum biology and how/where classical and quantum physics interact.

 

[Arakhor]

Apparently, it just came out. Colour me interested.

 

[hobbsyoyo]

No I hadn't heard of it before this.

 

[Birdjaguar]

Well, I was impressed by the evidence of quantum processes showing up as part of chemical interactions and enabling those chemical processes to happen in an improved fashion. The authors also opened the door to wider work that should be done.

This is from a book review and talks about one of the examples in the book:

But life, it seems, is different. Indeed the internal compass that enables female robins to migrate in the winter relies on a curious capability that wouldn’t sound out of place in an X-Men line-up: magnetoreception. The theory goes that the eye of a robin contains a chemical that, when it absorbs light of the right energy, can shuffle its electrons around. This shuffling creates a system that exists, thanks to some quantum jiggery-pokery, in two forms at once – each of which leads to a different outcome in the reaction that follows. Which form predominates, and hence which outcome is more likely, is influenced by the angle of the Earth’s magnetic field, allowing the robin to detect if it is heading towards the equator or away from it.

http://www.theguardian.com/books/20...khalili-review-weird-world-of-quantum-biology

From another:

Quantum mechanics is one of science’s most successful theories, superseding Sir Isaac Newton’s “classical” physics, the workaday version taught at school. The theory’s weirder predictions—spooky connections, tunnelling and the like—are not part of people’s everyday experience. They happen at a microscopic level and, it was thought, only under precisely controlled conditions. Experiments were done by the steadiest hands in the darkest labs at the lowest achievable temperatures.

But life is nothing like that. Plants and animals are warmed and lit by the sun, mostly, and tend to be squidgy, moving and watery. It had long been assumed that a living being is a poor laboratory in which to carry out quantum experiments. But in 2007 scientists who were trying to understand how plants gather the sun’s energy so efficiently stumbled across something strange: that energy was sloshing around in what are called quantum coherences. In effect, the energy is in multiple places at the same time and “finds” the most efficient route from where it is collected to where it is put to use.

This first credible example inspired other scientists to follow similarly bold avenues of enquiry. To grasp these new threads in quantum biology is to grasp a quantity of quantum theory; the coherence is just one of the complex phenomena that Jim Al-Khalili and Johnjoe McFadden set out to teach the reader. They succeed by using delightfully revealing analogies and similes, some borrowed from their prior work, that make slippery concepts sit still for study.

http://www.economist.com/news/books...helping-explain-mysteries-life-science-nature

 

[uppi]

Well, I was impressed by the evidence of quantum processes showing up as part of chemical interactions and enabling those chemical processes to happen in an improved fashion. The authors also opened the door to wider work that should be done.

The evidence has been out there for a few years now. Good to see that there are people trying to make the public aware of it.

From another:
http://www.economist.com/news/books...helping-explain-mysteries-life-science-nature

But in 2007 scientists who were trying to understand how plants gather the sun’s energy so efficiently stumbled across something strange: that energy was sloshing around in what are called quantum coherences.

I doubt they "stumbled" over that. The experiment was designed to look for exactly that. You don't perform that kind of experiment if you do not at least hope to see something.

 

[Birdjaguar]

"Stumbled" just makes a better story.

 

[dutchfire]

What is the current consensus on that? Seminars I visited a couple of years (2013?) ago said that it was still very controversial if/how quantum coherence influences photosynthesis.

 

[uppi]

What is the current consensus on that? Seminars I visited a couple of years (2013?) ago said that it was still very controversial if/how quantum coherence influences photosynthesis.

It is a very young field, so I am not sure there is something I would call consensus yet. And I have mainly heard talks by people directly involved in this research, who are obviously convinced that they are on to something. I have not heard anybody being overly critical and I have insufficient overview over that topic to say how strong the arguments of the (inevitable) critics are.

That said, my impression is the following:
- The quantum coherences are definitely there, at least in the systems that have been investigated. That means, any theory describing the energy transport in photosynthesis needs to account for quantum effects (or at least find reasons why they do not matter).
- People have wondered how the energy transport can be as efficient as it is.
- There certainly is evolutionary pressure to improve photosynthesis. Even an unlikely way to improve it by quantum coherence might have evolved and spread.
- There are toy models that show a convincing mechanism how coherences and especially its interplay with decoherences in biological systems could be advantageous for photosynthesis.
- I do not think anybody knows how well these toy models fit the real biological systems

In conclusion I would be very surprised if these coherences did not matter at all, but I doubt anybody has a realistic estimate how important these are on the scale of "very, very minor" to "life as we know it would be impossible without it".

 

[Flying Pig]

EDIT: I've done a bit of digging and it was a simple question, so I'd rather not bother everyone about it.

 

[Birdjaguar]

One of the book's authors on youtube:


Link to video.

The talk starts with the story of how the European Robin uses quantum action to navigate.

 

[illram]

Why are there no quasars "near" us? I.e., not even in our local supercluster of galaxies? Are they relics of a more chaotic universe from billions of years ago?

 

[brennan]

Yes..

 

[Flying Pig]

Does anybody have a rough idea of how quickly things like river meanders form? Is it a matter of decades, or centuries, or millennia? I can find plenty about how it happens but nothing that will give me a time-scale.

 

[Arakhor]

I was under the impression that the process was observable by humans, but it's been 20 years since I had a Geography class at school.

 

[hobbsyoyo]

Does anybody have a rough idea of how quickly things like river meanders form? Is it a matter of decades, or centuries, or millennia? I can find plenty about how it happens but nothing that will give me a time-scale.

All of the above.

They can happen extremely fast given the right circumstances (earthquakes for one) and can form oxbows and meanders in just a few days.*** Rivers are also continually eroding the ground around them and they can do this in ways that aren't at all apparent from the surface until they break through quite suddenly and shift course. So the change appears to happen overnight but had been in the works for years.

On longer time scales some rivers are practically in perpetual motion, constantly moving about (other than strictly downhill of course!).

But I think decades or at least years are a fair 'average' type estimate but it's so wildly variable that it's really hard to say what a definitive average is.


***Several US states (Illinois and Kentucky at the very least) have exclaves entirely within other states that happened when the Mississippi shifted course after major earthquakes over the course of a couple of days - far faster than legislatures could react to change the boundaries. Not that they would have changed the boundaries anyways - few legislatures voluntarily gives up territory!

 

[Cutlass]

Does anybody have a rough idea of how quickly things like river meanders form? Is it a matter of decades, or centuries, or millennia? I can find plenty about how it happens but nothing that will give me a time-scale.

It really depends on the terrain. Take the Grand Canyon. You can see places where the river course changed. But it took millions of years to make the whole canyon, and now it's so deep it doesn't really happen any more. That's through primarily sedimentary rock. Sandstones.

But if you take a strong but shallow river, the Mississippi is a good example, but it doesn't at all have to be that large, and the terrain is flatter and the ground is dirt and clay, then any given flood can result in a change in the active bed of the river. You ever hear of court cases where there was a land dispute because the boundary between properties was defined by a river, and the river moved? An earthquake could cause that, like Hobbs said, but the most likely cause was a flood. The river went over its banks and cut a new channel in the soft ground.

 

[Lohrenswald]

So this is probably stupid, but:
Does like the entire universe (or maybe rather the things in it) have a not-moving centre of mass?

 

[uppi]

So this is probably stupid, but:
Does like the entire universe (or maybe rather the things in it) have a not-moving centre of mass?

Probably not, but currently we do not know one way or the other.

If the universe is infinite, it obviously cannot have a center of mass. If it is finite, it could, but if this is because of space being curved and repeating itself, the center would lie outside of the universe (like the center of mass of a spherical surface, which is not on that surface). That means to define a center of mass you would need to define some kind of hyperspace in which space is embedded. But at that point you are already stretching the concept of a center of mass quite far.