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Your 8 quirky energy questions answered

- Curiosity

From Star Wars to hot curry to Einstein – we’ve got you covered.

Energy and electricity | Curiosity 15: #Energy ©

1. Can Star Wars’ lightsaber actually work?

Sorry to burst your sci-fi monster-slaying fantasy bubble, but the science doesn’t add up. There are two fundamental issues with the fictional energy sword used in Star Wars:

The first is that light never stops; it’s always moving at the speed of light. A lightsaber suggests that the light leaves the source and then abruptly comes to a stop at the end of the lightsaber.

The second issue is that science-fiction imagines that the laser light is very powerful. In fact, lasers are highly inefficient, maybe converting 10% of electrical power into light. So, for a high-power laser, you need even more power at the source – a small power station, in fact (and we know we can’t rely on Eskom). Now imagine the lightsaber in your hand, but with a cable connecting it to a very big power supply – not terribly awe-inspiring.

There are some tricks to try and get around these issues, such as using more efficient sources of laser light and using interference to make the light seem to disappear at the desired end of the lightsaber, but, so far, no one has made a working lightsaber. Distinguished Professor Andrew Forbes, Structured Light Lab, answers questions 1 and 2.

2. Is levitation possible?

We can’t promise that you’ll rise and float in the air from your own sheer will without physical support, but levitation is possible using very mature technology. You need a force pushing upwards to balance gravity pulling downwards. In fun arcades this is done by strong fans pushing air upwards. Another way to do this is with magnetism, and in fact you can buy toys that levitate magnets over magnets. On an industrial scale, the Japanese were the first to levitate trains – this removes friction so that the trains can go faster. Sir Michael Berry won an Ig Nobel prize for levitating a frog, and famously concluded his fun paper by promising one day to levitate himself!

3. Why do you get hot if your body temperature is 36°C but the air temperature is 30°C?

The normal core body temperature range can vary between individuals and can also be influenced by age, activity, and time of day. It generally ranges from 36.1°C to 37.2 °C.

Your skin is much cooler than your core body temperature because your skin is continually exchanging heat with your surroundings. We are continuously generating metabolic heat and we need to dissipate that heat to ensure that our core body temperature does not increase above 37°C.

When the air temperature is 30°C, the temperature gradient between your core and your skin is smaller, so convection and radiation aren’t enough to dissipate heat as fast as it is generated. Your skin has specialised receptors which can detect changes in skin temperature.  

When the air temperature reaches 30°C these thermoreceptors in the skin send signals to the brain and give you a feeling of being hot. To compensate, you need to sweat (which removes heat through evaporation), fan yourself (forced convection), or have a cold drink. ‘Feeling hot’ is your body’s warning signal to tell you to do one of these things. This warning system is controlled by the hypothalamus in the brain, which measures the temperature of the blood in your core. If you are outdoors, then the air temperature is not the major factor influencing your heat gain – it is solar radiation. Associate Professor Lois Harden, School of Physiology, answers questions 3 to 6.

4. Where does the heat in hot drinks go?

The heat from a hot drink will go directly to your core, the central part of your body.

5. Why does drinking hot drinks cool you down?

We all know someone who swears by drinking a hot beverage on a hot day, claiming it will cool them down – and the science agrees. Drinking a hot drink when it’s warm outside can cool you down, as long as you are not already sweating. That's because drinking hot beverages triggers your body's sweat response, without raising your core temperature too much. The sweat then cools on the surface of your skin which in turn reduces the feeling that you're too warm.

If you drink a hot drink, it does result in a lower amount of heat stored inside your body, provided that the additional sweat that’s produced when you drink the hot drink can evaporate. However, on a very hot and humid day, if you’re wearing a lot of clothing, or if you’re perspiring so much that it starts to drip on the ground and doesn’t evaporate from the skin’s surface, then drinking a hot drink is not helpful. Drinking a hot drink also causes peripheral vasodilation (widening of the blood vessels), which leads to an increase in blood flow to the skin. So as long as you are in a cool environment, you will increase dry heat loss too, but only for a short time.

6. What causes our physical responses to eating hot curry?

Most of us know the excruciating pain and bodily reaction to eating a super-hot curry – the runny nose, fiery tongue, and tears down your cheeks. That is your body reacting to capsaicin, the active ingredient in chilli peppers, that triggers receptors in the epidermal tissue that normally respond to heat, tricking the nervous system into thinking you're overheating. In response you will experience both the sensations and the physical reactions of heat, including vasodilation, sweating, and reddening or flushing of the face or neck.

7. Is teleportation possible?

Keen to skip Joburg road-rage and traffic congestion and simply teleport to your next destination? Teleportation is possible! In fact, it’s already being done! But there are some nuances …

Teleportation makes use of a phenomenon called quantum entanglement, where you have a pair of particles – photons, electrons, or atoms – that are sitting at the two separate ends of your teleportation ‘journey’. Let’s say one is in Pretoria and the other is in Johannesburg. The particles are always interconnected in some sense, much like a pair of coins that land on the same side whenever they are flipped and observed. Einstein called this ‘spooky action at a distance’.

Surprisingly, if we mix one of the entangled particles, say the one in Pretoria, with another that is imprinted with a message (auxiliary particle), we can transfer the information to the other entangled twin, located in Johannesburg. But the restriction is that the particle that had the original message (auxiliary particle) must be destroyed in the process such as to violate the no-cloning theorem in quantum mechanics.  

Put simply, information is transferred between two locations by destroying the original messaging while it reappears (transferred in a quantum way) elsewhere. And this is driven by spooky action at a distance (entanglement). So, to teleport, you must do so within the rules of quantum mechanics, otherwise it doesn’t work! Dr Isaac Nape, School of Physics.

‘Beam me up, Scotty’? 

It was Star Trek that let us imagine that we could simply step into a machine, say “Beam me up, Scotty!” and we’d instantaneously be in another location. However, teleporting is exchanging information between different media. So, is it possible? Realistically, we would have to ‘interact’ you with a superposition of ‘building blocks’ entangled over a distance. Provided nothing disturbed any of these fragile channels, you would be ‘re-assembled’ from new building blocks. If anything disturbed any entanglement, some of you simply wouldn’t make it through and, thanks to the no-cloning rule, the ‘you’ that was there before would be a jumbled-up mess, so you couldn’t go back. On the up-side, if it was successful, there would be no moral quandary. – Dr Bereneice Sephton, Wits Structured Light Lab.

8. What is E=mc2 and what does it mean?

E=mc2 is the mathematical equation that describes Albert Einstein’s theory of special relativity. It is probably one of the most famous equations in the world. However, while most people know the equation itself, very few people actually know what it means. In the equation, “E” stands for energy, “m” stands for mass and “c” stands for the speed of light. So, the equation reads that energy is equal to mass times the square of the speed of light. In simple terms the equation means that energy can be transformed into mass and mass can be transformed into energy. This means that even the tiniest objects hold a massive amount of energy. For instance, if you can turn the mass of all the atoms in a paperclip into pure energy, that paperclip would yield 18 kilotons of TNT – about the same amount of energy in the atomic bomb that destroyed Hiroshima in WW11 Professor Bruce Mellado, School of Physics.

  • This article first appeared in Curiosity, a research magazine produced by Wits Communications and the Office of the Deputy Vice-Chancellor: Research and Innovation.
  • Read more in the 15th issue, themed: #Energy. We explore energy research into finding solutions for SA's energy crisis, illuminate energy needs of people with disabilities, address the energy and digital divide in an unequal society, and investigate the origins of fire control.