# Special theory of relativity

Explain this, as if to a ten year old child. What model would you use to demonstrate it?

## 22 comments for “Special theory of relativity”

1. December 11, 2017 at 18:51

Knew that one would stump you with the cold addling your brain etc.

2. Toodles McGhee
December 11, 2017 at 19:16

Uh, sure, that’s the ticket! The cold addled my brain today….as does the heat. Actually, weather is a major brain addler-er-er to me.

3. dearieme
December 11, 2017 at 20:53

Dunno. I didn’t follow the arguments until I was (I suppose) 15. At 10 I presumably had other interests.

4. December 11, 2017 at 22:28

Can’t find the excellent vid I had on this earlier in the day. This one’s OK but wish I could find the other:

https://youtu.be/TgH9KXEQ0YU

The model used was light going up and down between two mirrors whilst those mirrors are stationary, relative to an observer at a distance.

Imagine it takes light 1 second to go mirror to mirror.

However, when those mirrors together move perpendicular to that motion [in other words, horizontally], that bouncing light must move further in the given time [obliquely, relative to a stationary observer at a distance … or in a zigzag] in order to hit the mirror.

It’s covering more and more distance in the same 1 second, relative to the distant observer. But not to someone stationary relative to the mirrors [that is – someone travelling with the mirrors]. To him, light is still taking that 1 second mirror to mirror.

To the distant observer, an alternatively view is it’s taking less time for the light to go the same distance … or time dilation.

The faster the two mirrors go horizontally, the faster time passes.

All this presupposes no gravitational effect.

This accords with Higham’s maxim that the more abstruse the concept, the more likely it is to be presented at an inopportune [or disadvantageous] time, such as in minus 2 temperatures or in heat, as Toodles mentioned.

The remedy for this is to point an AK-47 at said Higham and let him observe the relative speed of a bullet when travelling in his direction.

• ivan
December 11, 2017 at 23:35

James, can you prove that bit about relativity bearing in mind the Michelson-Morley experiment (speed of light) did not give a null result, just one that was half of the calculated result if it followed the aether hypothesis. This experiment was redone later with the same results but unfortunately a loudmouth believer in everything Einstein said was gospel managed to shout the results down so that discrepancy was never investigated (there were quite a few heated arguments in the letters section of Wireless World in the 50s early 60s about that).

If the speed of light has even a slight question about it it makes special relativity even more questionable because of the fixed observer and completely ignores, as you say, gravity and other physical effects.

• December 12, 2017 at 00:07

Do you mean Fresnel’s dragging coefficient?

• FrankH
December 12, 2017 at 00:00

Re: said AK-47 and said bullet. James is likely to invoke Xeno’s paradox and emerge unscathed. 🙂

• December 12, 2017 at 00:08

Let us give thanks to Xeno.

5. Wolfie
December 11, 2017 at 23:56

I started her at eight.

• December 12, 2017 at 00:09

Cryptic.

6. The Blocked Dwarf
December 12, 2017 at 00:11

“I’m in bed from the cold – are you too?”

No I despair of ever feeling warm again…and have felt that way since we moved here to Norfolk when I was kid. Once that North Sea Wind (“from Putin with love”) gets into your bones…
So I’m sitting here , waiting for the Tamazepam to kick in and practicing my “Rational Stenography” (a rather fascinating German shorthand system) and trying to find a workable mnemonic for the symbol for ‘W’.

Yep, just when you thought *your* life was sad….

• December 12, 2017 at 08:31

It’s a way of life.

7. December 12, 2017 at 04:00

Yep, we all ‘believe’ in relativity cuz the fyzics priesthood have the runes to prove it. And they have runes for quarks and leptons and other wozznames wot we cannot see, smell, snap on a mobile phone camera too. And we get our money reefed from our wallets to build temples of enormity underground without a by your leave just so those white-coated ones can worship at the Holey Torus. And some of those High Priests on a fat salary whack even claim there are other dimensions and other Universes out there that ‘just happen’. They have runes for those too.

But believe in God? Hah ! That’s just superstition, innit.

• December 12, 2017 at 11:07

Yep, we all ‘believe’ in relativity cuz the fyzics priesthood have the runes to prove it.

Of course. It’s true because it’s Science! That’s all you need to know.

Just like global warming is true. It’s Science! Of course in the 70s global cooling was Science! and it was true too.

• dearieme
December 12, 2017 at 11:18

I like a rant against physics from someone who likes to take snaps on a mobile phone camera. Just think, if God had given Moses a mobile phone camera you wouldn’t get all these rationalists pointing out that the Exodus never happened.

• James Strong
December 13, 2017 at 06:25

Physicists, with their theories, can explain and predict things.

Belief in God can explain and predict things too.
The sun rises each morning because God commands it to do so. That’s an explanation.
The sun will rise tomorrow because of God’s commands. That’s a prediction.

I don’t think the explanatory and predictive power of science and religion are equal to each other.
What do you think?

• December 13, 2017 at 08:35

I think there is the physical and then the metaphysical. There is something there with both, there are also limitations.

8. December 12, 2017 at 04:01

At present relativity is sending out the family Xmas cards and just as unpredictable.

9. December 12, 2017 at 08:32

Amfortas – how does God get factored in? Indeed.

Demetrius – why bother?

• December 12, 2017 at 10:31

He wrote the speed limit laws.

10. opsimath
December 12, 2017 at 16:41

Blimey — can’t you think of something HARD to ask 0: ?

• December 12, 2017 at 17:20

We like to ask the easy ones.