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### Author Topic: How do I explain general relativity to a six year old?  (Read 4334 times)

#### chris

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##### How do I explain general relativity to a six year old?
« on: 25/11/2015 10:24:57 »
I have been set the challenge, by the BBC Radio 4 World Tonight programme, to explain Einstein's theory of general relativity to a six year old, which Einstein claimed you could do if you'd understood it.

So, how do you think I should approach this, and what, would you say, is the bare minimum we should aim to include to give adequate coverage?

#### chiralSPO

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##### Re: How do I explain general relativity to a six year old?
« Reply #1 on: 25/11/2015 12:10:21 »
I think the main point to get across is that no frame of reference is special. You can start with something familiar like a car or train (probably best), and talk about how it doesn't matter how fast the train is going, everybody and everything within the train behave the same relative to oneanother as people outside the train behave relative to oneanother (special relativity).

Once this point can be made, then you can talk about falling/constant acceleration (probably best addressed in an example of an elevator). They should be aware of the extra weight they feel when an elevator starts.

I don't think it would be easy to talk about dilation of time and space, and I don't know how easy it would be for them to wrap their heads around non-additive speeds, but I think they could understand the concept of an ultimate speed limit.

#### puppypower

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##### Re: How do I explain general relativity to a six year old?
« Reply #2 on: 25/11/2015 13:37:01 »
The way I would do it is by beginning with the concept of energy. I would ask the question, which can build a bigger fire, one piece of wood or two pieces of wood? The child would answer, 2 because this has more wood to burn.

Say, I have the one piece of wood in this pile, and two pieces of wood in the that pile. Next,  I move the both piles so far away, so you can't see either one clearly. Now which pile can build a bigger fire the left or the right pile. The child will say, since I can't see well enough to tell which is which, I don't know, so either could be correct; relative.

But on the other hand, since I know one pile has one piece and the other pile has two pieces, the two piece pile, no matter which side it is on, will build the bigger fire. But since i can't tell the difference, left or right could be the right answer.

Relativity is based on not being able to tell which pile is which, in terms of energy. When we look out into space, we can't know for sure the absolute energy of each and every star. Therefore we can't make use of the conservation of energy, which is a law of science. With this loophole in the law, we can pretend both are the same, since nobody can prove otherwise. Einstein was telling us since we can't apply energy conservation, we will have to assume there is no preferred reference. because we have limits in terms of knowing energy.

In the twin paradox, the twin in motion comes back younger. If there was no preferred reference, each time we ran this experiment the opposite twin would be younger, like flipping a coin. This is not the case, since only the twin with the energy of motion; rocket fuel, is younger due to energy based relativity that sticks. The stationary twin may assume the same for himself, up the point the two meet so they can compare. If this occurs the loophole is made void and the answer is clear.

A good work of art that shows this is by the artist Escher and a work called relativity. In this art work all references look fine; no energy balance. But if we use any reference as the standard; energy balance, then we notice some of the reference are not real. It is like a magic trick.

#### puppypower

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##### Re: How do I explain general relativity to a six year old?
« Reply #3 on: 25/11/2015 17:42:57 »
The philosophy of science requires experimental verification and reproducible results. If we try to do an energy balance out in an expansing universe, we cannot always verify an energy balance. What that means is the inaccurate energy balance can run contrary to the spirit of the scientific method. We can only guess, but we can't verify. If had we had two rockets, both on empty space, without any landmarks to gauge, it is hard to tell exact energy or even who has the energy.

On the other hand, things like Doppler shift and red shift are things we can measure experimentally, and which can be verified by another lab. These observations, better fits the spirit of the scientific method. In the case of the two rockets in empty space, without any landmark, we can tell a relative velocity with both rocket references able to verify the same measured velocity.

What appears to have happened is since relative reference better fits the spirit of the scientific method, over a wider range of observation, than the harder to do energy balance, relative reference is considered more scientific in the sense of satisfying the spirit of the method better. But in cases where you can do an energy balance, relative reference does always work out. The twin paradox does an energy balance.

The original question was general relativity. In this case mass and energy have an equivalence, with the mass allowing us to do the energy balance for general relativity. If this case we don't default to relative mass based on which reference is looking. Mass/energy is absolute; conservation.

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #4 on: 25/11/2015 18:54:37 »
You need to begin with an experimental fact. Unfortunately I can't think of any that would be within the experience of a six-year-old, and the only one I can actually demonstrate is E = mc2 which is a conseqence of special, not general relativity.

#### jeffreyH

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##### Re: How do I explain general relativity to a six year old?
« Reply #5 on: 25/11/2015 19:45:07 »
I have been set the challenge, by the BBC Radio 4 World Tonight programme, to explain Einstein's theory of general relativity to a six year old, which Einstein claimed you could do if you'd understood it.

So, how do you think I should approach this, and what, would you say, is the bare minimum we should aim to include to give adequate coverage?

Start with: If you throw a ball up in the air will it take the same amount of time to go up as to come back down? Then if you roll a heavy ball and a light one down a slope which one will get to the bottom first? These are then simple experiments a child could carry out. Making measurements and recording times to show that these are facts. Then ask them how fast they think light takes to get from the light bulb to their eyes. When they answer ask them why they think this. Then give them the correct answer to see if they accept it. You can then compare this to the fact that they may have thought the heavier ball would roll down the slope faster. Once you have established that these events do not happen as you would intuitively expect then you can attempt to explain that time is not a constant everywhere. Good luck.

#### evan_au

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##### Re: How do I explain general relativity to a six year old?
« Reply #6 on: 25/11/2015 21:11:03 »
For General Relativity:
I would show them an Orerry or planetarium, to show the motion of planets & comets around the Sun, as discovered by Copernicus/Kepler/Newton.

I would then use one of those funnel models in the Science museum, and show how a coin takes on a circular or elliptical orbit as the attraction of a mass (like the Sun) distorts spacetime. This explains why the orbits are as Newton predicted.

For mass affecting light, I would point to Eddington's experiment, conducted a few years after the General theory of Relativity. So light behaves like other particles, in that it is attracted to the Sun, and its path is bent.

For gravitational time dilation, I would show a GPS receiver in a car, then the GPS satellites in orbit. The clocks on the satellites are further out of Earth's gravitational field, so they run faster than when they were being built on Earth. (I know this is slightly muddied by velocity time dilation.)

If you want to end this section with a bang, show a model of two pulsars spinning around each other, and spiraling inwards until they collide with a massive bang. You could conclude with the LIGO experimenters, closely monitoring their detectors, and hopefully looking for signs that this has happened somewhere in the nearby universe.

For Special Relativity:
I would start by explaining "Frame of Reference" with the Mythbusters episode with a soccer ball shot from a truck.
Something that seems to be moving to one person (on the truck) is not moving to another person (on the ground). No person's viewpoint is special.

I would move onto the speed of light as the absolute speed limit by looking at the LHC. Despite the huge amounts of power going into this machine, they can't get protons going faster than the speed of light.
Quote from: Wikipedia
move at about 0.999999991 c, or about 2.7 metres per second (6 mph) slower than the speed of light (c)
http://en.wikipedia.org/wiki/Large_Hadron_Collider#Design

Then I would introduce addition of velocities. Two beams of protons approach each other at almost the speed of light, in opposite directions. But if you measure the speed of the oncoming proton from the viewpoint of a proton coming the other way, it still doesn't exceed the speed of light (but it does exceed the number of digits in my spreadsheet, if you calculate it the obvious way!) That is mind-bending to an adult, but it probably wouldn't concern a 6-year old!
http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity

For time dilation at high speeds, I would point to the extended lifetimes of high-speed subatomic particles produced in the LHC.

And if you want to end this section with a bang, show a hydrogen bomb, and say that this is converting just 0.1% of the matter to energy (approximately). Introduce the iconic E=mc2, the best-known equation in Physics.

#### Thebox

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##### Re: How do I explain general relativity to a six year old?
« Reply #7 on: 25/11/2015 21:36:07 »
I have been set the challenge, by the BBC Radio 4 World Tonight programme, to explain Einstein's theory of general relativity to a six year old, which Einstein claimed you could do if you'd understood it.

So, how do you think I should approach this, and what, would you say, is the bare minimum we should aim to include to give adequate coverage?

A spiders web bends in the wind........a dripping tap can speed up or slow down,

#### evan_au

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##### Re: How do I explain general relativity to a six year old?
« Reply #8 on: 25/11/2015 21:47:48 »
Addition of velocities in the LHC: My back-of-the-envelope estimate suggests about 2mm/day slower than the speed of light, for the oncoming proton.

Method: The straightforward way does not work, so you have to represent the velocity of a proton in the LHC as v=c(1-x), where x≈0.000000009.

When adding the speed of two protons, where v1=v2=c(1-x):
Total speed = (v1+v2)/(1+v1v2/c2)
=c((1-x)+(1-x))/(1+(1-x)(1-x))
=c(2-2x)/(2-2x+x2)
≈c-2c/x2
≈ c - 2 mm/day

Another Illustration?
If you wanted to link Einstein's General Relativity to post-relativity discoveries, you could show the highly distorted images of distant galaxies whose light is magnified and bent through gravitational lensing around (we think) the Dark Matter halo which surrounds galaxies - you could even point to the one called the Einstein cross (although there are some that are more visually dramatic).
http://en.wikipedia.org/wiki/Einstein_Cross
« Last Edit: 25/11/2015 21:50:50 by evan_au »

#### Colin2B

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##### Re: How do I explain general relativity to a six year old?
« Reply #9 on: 26/11/2015 09:06:32 »
I think the main point to get across is that no frame of reference is special. ........
I think ChiralSPO's suggestion is closest to the brief. If you use the train eg you can point out that you appear still and the countryside is moving, and when you overtake the overtaken can seem to go backwards. Eg inside a tunnel it can be hard to decide who is moving. You could use the eg of 2 children cycling side by side, relative speed, and as seen by a pedestrian. Then get them to imagine space rockets, how do you know who is moving? From one POV they are moving, from another the 'pedestrian' is moving. You could explain that at first people thought you could use the speed of light to determine who is moving, but that doesn't work and shows us that when things move very fast, near light speed, time and length aren't the same as we think they are when they are not moving relative to us.
Good luck, I'm not sure Einstein was right.

Edit: sorry, missed out the GR bit. Yes, use elevator and car accelerating to show equivalence or the feeling of weightlessness at the top of a swing's arc.. Could you use analogy of a big sand pit, flat and a ball rolls straight across, but put a hollow in the middle the ball will be deflected.
I never really like this type of analogy because a smart 6 yr old will say it is only deflected because we have gravity under the sandpit/rubber sheet. But it's probably the best we can do.
« Last Edit: 26/11/2015 11:29:56 by Colin2B »

#### evan_au

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##### Re: How do I explain general relativity to a six year old?
« Reply #10 on: 26/11/2015 10:34:59 »
There is also the discovery by Hubble (the man, not the orbiting telescope) that the universe is expanding.

This is one of the solutions of Einstein's general theory of relativity (if you set the cosmological constant =0).

Some people try to picture this expanding universe with galaxies as dots on an expanding balloon.

PS: You can also picture the path of photons passing the Sun on one of those funnels in the science museum; you just need to roll your coin with a high speed, so it goes flinging off the other side - but its path has been slightly bent. The speed of the photons doesn't really change in a gravitational well, but their energy/frequency does. The  bending of spacetime near a mass causes the path of light to bend.

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #11 on: 26/11/2015 14:59:26 »
Once you have established that these events do not happen as you would intuitively expect then you can attempt to explain that time is not a constant everywhere.

But it is! That is the essence of relativity: the atomic clock runs at the same rate as seen by an observer who is stationary with respect to the clock, regardless of their position in space or constant velocity. It just looks different to a moving observer.

#### timey

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##### Re: How do I explain general relativity to a six year old?
« Reply #12 on: 26/11/2015 17:42:41 »
Alan, of course that is true regarding the moving clock, but what about the NIST ground level experiments?

2 identical atomic clocks, 1 placed at ground level and the other at 1 metre elevation.  Both clocks are stationary with respect to each other, and the experiment observer is also stationary with respect to the stationary clocks.

The elevated clock is recorded as ticking at a very slight faster rate than the ground level clock.

Chris, you could ask the six year old if he/she lives on the ground floor, or in a high rise flat.  You can explain that a person living at elevation is experiencing time at a slightly faster rate when they are at home, and will age faster than a person living at ground level.  But not to worry, because the difference is so small that it will amount up to only around a minute over a period of about 79 years.

You could then say that if one of these elevated clocks were flown away from the planet earth up to radius = 1.497, that while the increasing elevation that the clock experiences will increase this clocks rate of time, that the velocity that the rocket must travel at to escape gravitational pull will slow the rate of this clock down.  At radius = 1.497 these effects cancel each other out.  You could show the child a visual graph of these effects and explain using more simple language. (I really wouldn't mind having a look at a graph like that myself tbh... chuckle)

The train scenario is a great one for kids.  I remember it well how the sensation of experiencing the visual information that I was moving in relation to the physical information telling me I was stationary, making me feel quite odd as a child.

Good luck with it!

#### evan_au

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##### Re: How do I explain general relativity to a six year old?
« Reply #13 on: 26/11/2015 18:17:04 »
Quote
explain Einstein's theory of general relativity to a six year old, which Einstein claimed you could do if you'd understood it
This is quite a challenge!
Firstly, to narrow down the scope so that you just explain General Relativity, without first having to explain its basis, Special Relativity.

We can come up with illustrations that show some of the effects of GR (eg in 2 dimensions, rather than 3, or using GPS as an example), but it is another to show the reason for GR to have these effects.

Some of the illustrations that are understandable by adults (eg paper graphs) won't be meaningful to 6 year old children.

Perhaps we could conclude that Einstein had very bright children, or that he was better at Theoretical Physics than he was at Child Psychology?

Anyway, Chris, please point us to your result - it would be interesting to hear it!

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #14 on: 26/11/2015 19:30:58 »
2 identical atomic clocks, 1 placed at ground level and the other at 1 metre elevation.  Both clocks are stationary with respect to each other, and the experiment observer is also stationary with respect to the stationary clocks.
But an observer at the higher level would be at the same gravitational potential as the higher clock. Eeven so, this doesn't answer the question: whilst you might state this fact to a six year old, you'd be hard pushed to demonstrate it and several lightyears away from explaining it.

The difference between science and religion is that science is demonstrable and explainable. Please don't present it as religion!

There's no shame in not being able to explain GR to a kid "from cold". A good friend invited me to a party to celebrate his PhD in history. I congratulated him and he said "It's just a question of hard work. You could pick a day in the past and start researching it tomorrow, explaining what events led up to the headlines, or whatever, and get a PhD for it. If I wanted to write a thesis on the color of charmed quarks, it would take me five years just to understand the question."

So I'd be inclined to have two bites at the cherry. Start with SR, and if the kid is interested, generalise it, just as Einstein did.

#### timey

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##### Re: How do I explain general relativity to a six year old?
« Reply #15 on: 26/11/2015 20:26:05 »
Alan, I would not dream of presenting anything as a religion.  I'm not sure where you are coming from with that!

The facts I have stated have been presented as science by NIST in 2010 as per experiment, and reported as proof of GR, inclusive of the ratio if 1 minute difference over 79 year period (or thereabouts) for high rise flat, in 2010 by national newspaper such as the Independent, or perhaps it was the Guardian. My memory fails me as to which, perhaps it was both.

Also I believe that any self respecting six year old would understand a short graphics animation that depicted a velocity trajectory in mph, and a velocity time dilated clock in relation to an elevation related clock showing time dilation in relation to the rockets elevation.  The rocket dash board clock could show the difference of the elevated time dilation in relation to the clock on earth, minus the difference between the velocity related time dilation in relation to the clock on earth, this then 'being' the time that the clock on the rocket 'is' experiencing.  At radius = 1.497, the difference between the time of the elevation time dilation related clock in relation the the clock on earth, minus the difference between the velocity related time dilation in relation to the clock on earth, you will find that the rockets dashboard clock will register the same time in relation to the clock on earth.

Please excuse me if I am wrong, but I don't think I am.
« Last Edit: 26/11/2015 20:56:46 by timey »

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #16 on: 26/11/2015 23:58:05 »
Also I believe that any self respecting six year old would understand a short graphics animation that depicted a velocity trajectory in mph, and a velocity time dilated clock in relation to an elevation related clock showing time dilation in relation to the rockets elevation.
Buit why would he believe it, except that you have told him it is true? He will have seen animations of cats being crushed by falling anvils, Homer Simpson strangling Bart, and a whole lot of other nonsense. He will have heard fairy stories from Grimm to Revelations via Genesis and with any luck will have retained suficient skepticism to reject them all as nonsense.

You have to begin with an actual observation that he can make, or preferably already has made, that can be entirely and only explained by GR. Otherwise you will at best get him to parrot a few equations, which is not the same as understanding or even believing in what you have told him. And there's the underlying problem: GR effects are way too subtle for 99.999% of humans ever to have observed the difference between GR and classical mechanics.

I've long advocated teaching quantum mechanics rather than the shell atomic model or wave-particle duality, because you can observe quantum effects quite easily (why are street lights yellow? why can I run a red LED from a lower voltage than a blue one? why does a geiger counter go "ping" at random intervals?) so you might as well teach the truth from Day 1 and show how you can use a continuum approximation for very large systems, rather than have to confess every day that yesterday's lesson was bullshit. But without a simple demonstration of a mesoscopic effect, you don't have a starting point for general relativity.

#### timey

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##### Re: How do I explain general relativity to a six year old?
« Reply #17 on: 27/11/2015 00:16:29 »
Ok Alan, I get where you are coming from now, but surely these quantum observations are in as much as in the same league as explaining how these time considerations are why the voice in mummy's car always knows where the car is?

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #18 on: 27/11/2015 10:10:41 »
It's pretty easy to explain satnav using classical mechanics. Essentially it is the same as radar ranging with the signal coming from several places, and you can demonstrate that with a thunderstorm or even distant fireworks:

"You see the flash before you hear the bang, and the further away it is, the bigger the gap, so sound and light travel at different speeds. It happens that light and radio waves travel at the same speed,(though much faster than sound). Now suppose we have two radios that transmit at the same time, but they are at different distances from us. If we measure the time between the signals arriving, we can work out how far apart they are. If we have lots of transmitters scattered around the world, we can work out where we are by measuring the time diference between all the signals".....and so on, with any degree of detail you want. GR is not first-order essential to explaining satnav - it is a correction factor, comparable with the non-sphericity of the planet.

Anyway, the voice in my car tells me where I would have been 5 years ago, and politely suggests that I should update the database occasionally instead of swearing at the machine.

#### jeffreyH

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##### Re: How do I explain general relativity to a six year old?
« Reply #19 on: 27/11/2015 12:19:25 »
Once you have established that these events do not happen as you would intuitively expect then you can attempt to explain that time is not a constant everywhere.

But it is! That is the essence of relativity: the atomic clock runs at the same rate as seen by an observer who is stationary with respect to the clock, regardless of their position in space or constant velocity. It just looks different to a moving observer.

In inertial frames that are equivalent I will grant you.

#### lightarrow

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##### Re: How do I explain general relativity to a six year old?
« Reply #20 on: 27/11/2015 16:07:09 »
"How do I explain General Relativity to a 6 year old?"
This way:
"Grow, study physics at university, theoretical physics specialization, and then you will know something of General Relativity".

--
lightarrow

#### timey

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##### Re: How do I explain general relativity to a six year old?
« Reply #21 on: 27/11/2015 20:20:03 »
I dunno lightarrow, this is pretty definitive.

http://m.huffpost.com/uk/entry/8638750

#### alancalverd

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##### Re: How do I explain general relativity to a six year old?
« Reply #22 on: 28/11/2015 00:34:15 »
Stretchy fabric spacetime demonstrations look good to people who already understand the subject. But as far as a six-year-old knows, everything falls in a straight line, downwards, and the moon is just another light in the sky, that tyakes as long as the sun to go round the earth.

I think you might be right about satnav: it's an everyday phenomenon, as is the radio. So we can talk about radio waves and navigation by time differential because our audience will at least be familiar with the phenomenon. So we need to have very accurate clocks in the satellites because the time differences are very small. But it turns out that although the clocks keep exactly the same time as each other, they actually run a bit faster than the same clocks on the ground. The difference is predicted by somethign known as the theory of general relativity.

OK, now we have attached the name to a phenomenon that is demonstrable by analogy (you can vary the speed of a metronome to emphasise the point) but that's still a hell of a long way from an explanation!

#### timey

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##### Re: How do I explain general relativity to a six year old?
« Reply #23 on: 28/11/2015 01:33:52 »
But Alan, I think you may be stretching the remit of the challenge a little here.  Explaining general relativity is a far cry from giving an explanation of general relativity.

An explanation of general relativity suggests that one is aware of why general relativity is as it is.  One might attempt to explain general relativity to a six year old, but the inevitable 'why' question will surely have to be answered as: "we don't actually know why, we just know that it fits observation".

I agree.  I also think the sat-nav is the way to go.  I think the high rise flat difference in time would be an excellent lead in, and could get a laugh if presented in comparison to a friend who lived either higher or lower than the six year old in question:
"...but your friend will not end up going to big school before you, because if you and your friend were to live in the same homes until you are both 79 years old, your friend will only be 1 minute older than you"

I'm presuming that it is a prerequisite that it wouldn't really quite be cricket if the six year old wasn't already proficient in telling the time?

#### rebeccaspears

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##### Re: How do I explain general relativity to a six year old?
« Reply #24 on: 28/11/2015 03:53:38 »
Rub a balloon with a cloth to induce a charge which will demonstrate "static cling", then attract small pieces of paper with the balloon. Once they see that static electricity attracts the small pieces of paper to the bottom of the balloon, then you can start explaining to them about 'the force'.

Take a magnet and hold it vertically, sprinkle iron fillings on either side of the pole. Iron fillings on the bottom side will be hanging. Then the child will get a feel that, it is possible for things to stay without falling down. You need not explain the concept of gravity for the child now. The child will create the explanation for itself (might also become next newton by creating a new concept).

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##### Re: How do I explain general relativity to a six year old?
« Reply #24 on: 28/11/2015 03:53:38 »

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