Answers to last issue's Do You Know?

1. Since the earth rotates, can we not design a lift that transports people up, and waits until the destination comes, then brings them down?
Ans: That's not a bad idea, but see what will happen when you try some thing like that. You, the Earth and the atmosphere are constantly moving very fast as the Earth rotates. How fast is the Earth moving due its rotation? Well, it's moving at about 1,670 km an hour which means that if you did sort of hover at rest above the spinning Earth, the wind speed you feel would be 1,670 km an hour. There is another problem: how would you stop at all after jumping up? But we will take it up later.
So what can you do against such a wind? That would be impossible to deal with unless you had an aerodynamic object like an aircraft with engines to hold yourself against the wind and that's exactly what an aircraft is. Concorde for instance could fly the equator at about 1,670 km an hour and could stay still essentially. It would hover above the Earth. The Earth would be spinning around underneath it and it would then land somewhere else. If there were no atmosphere, it does not solve the problem because we then do not have aerodynamic lift to hold the plane up. 
So, we have to go into orbit and going to orbit, the speeds there are even bigger, roughly 35,000 km an hour and that requires a lot of fuel and a spacecraft. Thus, get out of the wind and up into orbit and the fuel you would have to consume to get there would far exceed the fuel used by a plane which uses the wind currents to their advantage. 
Another point is that as Newton worked out, objects keep moving at the same velocity unless a force is applied. So, stopping from speed is just as tricky as starting to get to speed in the first place. Thus even in an airless world, lift style travel across the Earth using its spin would still use up energy and would not be that different to other modes of transport. 

2. Do plants die of old age?
Ans: Well, think about this. How old do you think the oldest plant is on Earth? Thousands of years, right? Think of giant sequoia and redwood trees. So, would it surprise you then that actually, the oldest plant on Earth is at least 43,000 years old! It may actually be 135,000 years old. It is a Lomatia, Kings Lomatia and it was found in south western Tasmania in the 1930s and the person King who found it sent it off to the Botanical Society and they called it King's Lomatia in his honour. It has subsequently been examined in more detail.
This plant clearly cannot reproduce because it's got three copies of its genetic material in its cells which means that it's genetically incapable of producing any seeds. So, the plant can only grow by effectively cloning itself. In other words, a bit of the plant digs into the ground and puts down some roots and makes another side spinoff plant. So, the tissue is slowly growing and growing from the same stock that has been there for all that time. 
How do they know how old it is? Because they have found in the same
region, as the plants that are growing now in just one tiny part of
Tasmania in south western Tasmania in Australia. They have found
remnants in the fossil record going back at least 35,000. If not,
135,000 years of plant tissue resembling very precisely this existing
plant. They have carbon dated it to those ages. So, it looks so similar
that they are happy to conclude that it must be the same plant and
therefore, it must have been growing there for at least 135,000 years,
possibly longer. And there are some pine trees which are of the order of 4,500 years old. So, there's certainly a lot of old stuff in the plant world. 
The trick here is that it has got to be able to replicate its DNA, but without introducing errors along the way.
When plants are that old, they have been replicating their genetic material for that long. But then a plant has a much lower metabolic rate than us. That being the case, when you copy your DNA and you grow your cells very, very rapidly, they are less likely to get damaged if they don't have this highly damaging environment that a fast metabolism like ours tends to breed. This is probably why the trees are able to be more resilient and live for these extended periods of time.

3. How strong are gorillas?
Ans: An adult gorilla is about 6 times stronger if you are talking about upper body strength than an adult human. If you think about it, that makes sense because although gorillas mainly walk on the ground now, much more recently than us, they were swinging in the trees and they needed strong arms. Even now, they walk sometimes on all fours. So, their arms are much more used to support themselves than ours are and that's probably one of the reasons that they're so strong. They are actually remarkably gentle in the wild so although they could do a lot of damage, they don't tend to. 
People can get close to gorillas and they are very mild. They are curious about us. The most intelligent animals which are the primates, the dolphins and whales and also birds like crows are all very curious, very interested in us and very intelligent.

4. How old is the Milky Way?
The way we start looking at how old our galaxy is, is by looking at the contents of it, so we look at the age of the stars that it contains. We do know the age of the Sun and the Earth. It's about 4.5 billion years old. If we look at the stars in our Milky Way, we find that some of them are actually about 13 billion years old. We can say they really date back to the very, very early beginning of the universe.
Then we can wonder whether what we see are younger stars. It is possible that there is even an older generation of stars which have already died out, but to settle this, we can look at the abundance of heavier elements within our galaxy. These are only formed in supernova explosions, that is, by the death of stars or through so-called cosmic ray interactions. This gives us an idea of how old our galaxy must be, some thing like carbon dating. Some estimates put it at about 13.2 billion years old.
That gives you a rough answer, but if you are thinking about the actual shape of the spiral galaxy itself, that is probably much younger. That may be 10 billion years or so, for it to actually have built up into the structure that we recognise today as our Milky Way.
Still it is pretty old, when you think that the universe as a whole is only about 13.8 billions years old. Does that mean that pretty much all the galaxies came fully formed very quickly after the big bang? The answer is yes -- quick in the timescale of the whole universe, but they did build up from the big bang. Initially, they were just small perturbations. The local areas in the universe that were denser then others started to form stars. The stars gravitationally bound together into globular clusters. We believe that there was a hierarchy building up into the galaxies that we recognise as spirals and elliptical galaxies.

5. Does time stop for photons travelling at the speed of light?
Ans: Yes, that is right, though it seems a very strange thing indeed.
If a particle is approaching the speed of light and had a clock on it, we as observers of that particle going extremely fast would see that time slows down and approaches this sort of eventual stopping. It is impossible to imagine the frame of reference at the speed of light - special relativity does not really deal with that. It takes the speed of light as a constant and that is regardless of what speed you are going at. So, even if you are travelling at 99% of the speed of light, you are still measuring c as c. In that sense, it is difficult to answer what kind of time the photon is experiencing. But we are just saying that if you were a particle, perhaps travelling at 99% at the speed of light, in your own frame of reference, then time is moving normally. You have a much faster ticking clock compared to the observer that sees that time has nearly slowed down.
Actually, you have probably heard of this, but we have experimentally confirmed such `time dilation' here on Earth. There was an experiment back in the 1970s that put atomic clocks on commercial aircraft and had them fly around the Earth, both in the eastward direction and the westward direction, and we were able to compare, once they got back on Earth with some naval observatory clocks. There was an actual difference because they were moving faster than the Earth's rotation at some point. 
You have probably heard of this too, the great pyramids also distort time because they are very massive and so, they bend space time. So, time travels at a different rate. Any time you go near something very massive, time changes. If you go to Egypt, sit next to a pyramid, time is distorted for you, actually. To extend this even further, if you go to a black hole and start falling into a black hole, your observer (outside) is seeing that time has nearly stopped for you as you fall towards it because you have warped that time so much.
Lots of interesting things going on, isn't it? Thinking about travelling at the speed of light or sitting near some thing very massive can get your mind going.

6. How do we know the Earth's core is solid?
Ans: It was discovered that the inner core of the earth was solid because 
shear waves had passed through it and they cannot pass through a liquid. Since the inner core is solid and the outer core is liquid, how did the shear waves pass through the outer liquid core in order to get to the detectors?
Mainly, there are two different kinds of waves. One is Earth's Corea pressure wave. It is like a sound wave whereby the movement, the wobble, is in the same direction as the wave is travelling and the shear wave is like a wave on a string, it is at a right angle to the way the wave is travelling. In a liquid, you cannot get any shear waves except on the surface. So, in the bulk of a liquid, in the body of a liquid, all the waves must be pressure waves. This is so for a fluid of any kind, in gases as well. But at the surface of a liquid, you can get shear waves and you can get shear waves created when a pressure wave hits a surface.
Thus, basically, the way they found out that the centre of the earth is solid is this: 
* When waves created by earthquakes on the surface go down, they hit the liquid outer core.
* Then when they go from a liquid outer core into the solid inner core, you get an extra wave going off at right angles in a strange direction.
This could only be because of a shear wave. You see the results of that coming out through the liquid outer core and bouncing off to an earthquake station on the wrong side of the planet where it should not be. The only way you can explain those waves getting to the earthquake station there is if the centre of the earth is solid and there is a shear wave going through it. 

Sources:
Univesity of Cambridge, The Naked Scientists, Scientific American.