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Hey everyone. Thanks so much for all the awesome tweets, Facebook messages and blog comments you've been posting about The Secrets Of Everything. It was lots of fun making a series that tried to answer those brain-tickling FAQs we've always wondered about, and I had an absolutely blast filming it – even getting buried alive and being shot in the butt with an air rifle! It's ace that you guys have been enjoying it. Cheers for the #AskGreg questions you've sent in too – there were some absolute crackers, so I've picked out a couple to have a go at answering...

cusker87 asked... Is it possible to travel back/forth through time?ÌýAnd if it is possible, how far can we actually travel?

Oh man, that's a big one. And a major head screw!

Ok, here goes: The reason some people think time travel could be possible is down to Einstein's Theory of Relativity. Over 100 years ago Einstein was sat pondering one of his famous thought experiments when he hit on the idea that you shouldn't see space and time as separate things, but actually as an interlinked 4-dimensional thing called "space-time".

Basically you need to take your 3 dimensions of space (left/right, up/down, forwards/backwards) and add in another for time… Kinda tricky to imagine! Then, what you need is a wormhole – kind of like a tunnel through that 4d space-time - that would theoretically allow someone to move from one time and place to another time and place in the blink of an eye…

So, yes, time travel *is* theoretically possible. Whether it's actually do-able is another matter! Physicists reckon travelling *forwards* in time is all good. After all, Einstein's Theory of Relativity says that if you travel around the universe at close to the speed of light, when you come back to Earth you will have aged less than those who stayed on our planet. So technically you'll have travelled into the future where they're older than you.

What physicists aren't so keen on is travelling *backwards* in time. That's because of the time-travel paradox – what's to stop someone going back in time and killing their grandfather before their father is conceived?? There is a work-around that involves multiple universes but then it gets even more complicated. I think.

So, that's briefly the theory. But in practise? Who knows. One thing though, if time travel is possible, why haven't we met someone from the future yet? Or maybe we have…

Charlie asked... Is there a sound frequency that can make you loose control of your bowels?

Ah ha, the famous "brown noise"! I love this idea.

Think of someone trying to smash a wine glass with their dulcet tones. Sound travels in a wave and is just a series of compressions and decompressions. When that sound wave hits the glass it sets it compressing and decompressing too. If the frequency of the singing matches the glass’s particular "resonant frequency" those compressions and decompressions get amplified big time. Hit a glass with a sound of that particular frequency at a high enough intensity and you can smash it.

The same principal works with your bowels! In Episode 3 we had a look at whether sound could kill you. Using a whole bunch of huge festival speakers I showed that high intensity, low frequency sound could set your organs vibrating and rippling. That’s because that particular note – I think we were down in the 128Hz rang – is very close to the resonant frequency of those organs. So if you can get a note at the resonant frequency of your bowels you could, in theory, set them vibrating a LOT, and that could mean you lose control of them…

However, in practise, the music you get at gigs and festivals isn't actually loud enough to cause you an underpants issue. Plus it’s constantly changing frequencies so you don’t get that sustained impact that could lead to a messy situation…

If you’ve got any other FAQs drop them in the comments below, or send them my way on twitter - . Hope you enjoy the final ep on Sunday – I'll be trying to dig to Australia, seeing why fast food can make you fat, and looking at whether you can die of a broken heart...

The last episode of Secrets of Everything is on Sunday at 7pm.