No-one knows how explosions work (yet) 

An update from Sam, the scientist in the video! He says: "It's been great reading through your comments and seeing people excited and intrigued by our research. I thought it'd be useful to answer some of the common questions that keep cropping up: 1. Yes, high speed video/photography of explosions is nothing new. They did this all the way back in the 40s and it's famously how GI Taylor estimated the yield of the Trinity test. Our high speed video is not what gives us the new scientific insight, but it does help give us a steer as to what is going on, and it's a fantastic way to demonstrate what an alien world it is so close to an explosion (in time and space!) 2. Our pressure measurements from the MaCE rig do give us the new scientific insight. If you want to see an example of our recorded data then please feel free to read our recent paper (link in description), Figure 5. We're measuring pressures higher than the strength of normal steel that are applied and removed in 50 microseconds. For comparison, a blink lasts >100 milliseconds, so over two thousand times longer! 3. Scientists know a lot about nuclear explosions, that's true. There, the energy is released effectively instantaneously and effectively as a point-source. With high explosives, the reaction rates are comparatively slower. That means we have an ongoing chemical reaction that changes if/when the blast wave and fireball come into contact with structures. The exact loading applied to said structure is a function of the pressure-volume-energy state of the fireball, so there's an intricate dance between the two (pressure and reaction rates). This is where current models break down. Yes, even the sophisticated physics-based ones. 4. We're only just discovering the extent of our ignorance, because until now we simply haven't had the experimental data to compare to. We do know that these secondary reactions are significant, which makes explosions (from high explosives) so difficult to simulate, because we've measured explosions in normal air and in an almost pure nitrogen environment. 5. Yes, the mottled/bumpy surface of the fireball as it expands outwards is a genuine physical feature, and seen at larger scales too (see photos of the "Minor Scale" test). When we're performing tests that we intend to publish we form our explosives into a 3D-printed mould, but even then we still see these features. 6. We filmed at 250 thousand frames per second for this video, but our camera can go all the way to 10 million frames per second. Thank you once again for showing an interest in our research. Cool, innit?"

It does make sense why it's difficult to observe what happens in an explosion up close

3:17 Tom: “What’s the use for this?” Researchers: “Uh, because *it’s rad?”*

You can always tell it's going to be a cool video when we see High Visibility Tom Scott appear.

I’m imagining the researchers pausing for moment when Tom asked what the purpose of this was and they had to fight the urge to say “because explosions are cool”

Tom is the only person that makes a saftey vest look like reasonable casual wear.

If you go to 5:06 and use the . button to go frame by frame, you can see that the ground lights up 1 frame before the explosion is visible. This is because the camera scans in "lines" of pixels top to bottom. When it was at the explosive material, it had not gone off yet, by the time it got to the ground, it had.

The best of these videos are when the chaperone is as giddy and excited about the tech as Tom is.

Always amazes me that a scientist 100 years ago can think up theories that we can only test today.

I love it when a sciency person says, "We don't know what we don't know", it's both so true, and so honest.

The actual data from this test didn't make it into the video (it's just a LOT of numbers), but there's a paper in the description for those so inclined! And this week's pinned-comment plug: the Technical Difficulties are back! A new season of four adventures from me, Chris, Gary and Matt over at ru-vid.com - one every Thursday.

Oh hey, this is something I actually do active research and development on! We’ve actually gotten pretty good at making computer simulations of these kind of explosions using multi-phase physics models. The Kingery-Bulmash model that Tom mentioned is still used in places, but it’s ridiculously simple compared to real simulations.

tom scott is THE cool guy that doesn't look at explosions

Sam was my lecturer in the blast protection module of my civil engineering degree. Fascinating subject and a great teacher.

5:51 interesting to see the shockwave resonates the dust under the table. Wonder what impact this has on the signals within the data cables which run out from here and if a deflector would be beneficial

It’s amazing how many things there are that people had theories about how they worked 100+ years ago, and yet we’re either no closer to actually knowing or we’re JUST getting into it, like this

Nothing a scientist loves more than someone who obviously appreciates their work, you could see how chuffed he was at Tom's genuine amazement.

I love how jealous Tom looked when he was told the camera recorded a quarter million FPS. Like, that was just as much a highlight for him as the explosion

The last two utterances in this video encapsulate why I watch Tom Scott videos: his genuine desire not only to allow people passionate about interesting things to explain them, but also to *get excited along with them*.

No-one knows how explosions work (yet), but Tom Scott will be there to tell us, for sure

That feeling when you're just graduating from Sheffield and you didn't even realise that your uni was doing thing.

I get that its built for different forces and that, but its quite funny seeing this box delicately lowered to the ground by the forklift before it's blown up by an explosive

"Remember kids, the only difference between screwing around and science is writing it down."

This video is pyrotechnically correct. The best kind of correct.

I can't be the only one who was kinda expecting to hear Slow mo guys music at 5:17

Tom, this has been a game changer video. I cannot understate how much this has solidified what I want to do as a career. I’m currently working on a forensic science degree and have been thinking of doing something like explosives and/or fires. Yes, I do definitely want to do this. This blew my mind up with it! Thank you!!

It's amazing how the black and white slow mo looks exactly like those still frames of the Trinity explosion, which was 186,000 times bigger.

The multiscale/multiphysics and tiny timesteps required to simulate this stuff is so complicated. Data like this is used during validation and uncertainty quantification for models.

Wish I had this video about 4 months ago, my dissertation was about simulating fires and part of the background was saying why we couldn't/ it's so difficult to simulate explosions! Nice video once again 👌

1:07 Really should be called the Senior Lecturer in Big Booms

Ooh! The HSE labs :) fascinating place. Built on top of RAF Harpur Hill, in its day it was the second largest munitions dump in the country - a honeycomb of concrete bunkers built in a disused quarry before being backfilled to look like a hill again. Also one of the locations where the MOD dismantled and studied the German vengeance weapons of WW2...

This looks like a job for the Slo Mo Guys 😁

The dust coming off the large concrete pad is really interesting - shows how much energy is in even that 100g of explosive

4:54 "We kinda don't know what we don't know" -Mr Pioneer the engineer, 2023

Last year I worked for a MACV-SOG/SEAL veteran, who works for the Department of Defense. He’s been mapping the surface areas of expanding blast waves as an engineer. I learned new applications of Brownian Motion from him.

Now do a video of you going through Heathrow security. I once visited an explosion test site and then had a very interesting discussion at the Airport…

We had this problem when designing our detonation rig at the University of Southampton. We needed a way to collect experimental data that wasn't just qualitative, and it was incredibly difficult to find a sensor that we could expose directly to the detonation on the inside of a detonation chamber that could read data fast enough, resist the 3,000 Kelvin instantaneous temperature, and sustain anywhere from vacuum to 60 atmospheres of pressure. Using strain gauges is a cool idea to look at detonation wave speeds, but I don't see how they can read static pressure and temperature with time

At 05:13 : Tom's got the face of someone who's going to spend the next 12 hours searching for the right frame 😅. Fortunately, it didn't take that long.

Interestingly enough this is a similar problem that we have in lightning research, in the sense that you cannot get close to the object you are studying. So maybe their research can also benefit lightning researchers in their efforts!

The "kick vs push" question is similar to the "what is a dot?" one. if you look far enough, everything is a dot (just like everything is a kick if you speed it fast enough). It becomes interesting if you zoom in the other direction. :)

Damn, filmed at about 250,000 fps, giving The Slow Mo Guys a run for their money. 5:10

Wow! Look at that HUGE lego at 4:35!

I feel like, as a result of so many encounters with so many different phenomena, Tom has begun to intuit some of the observations these scientists are making. A sort of "wait, wait, don't tell me! Let me see if I've got this right!" thing.

1:00 ah yes the Tom Scott red shirt flag has been raised to alert everyone of his presence

I could easily observe an explosion up close in detail. At least once.

It almost looks like a fractal pattern when it’s exploding, as if it’s pushing in a set path.

Yooooo....mixing in some "Slow Mo Guys"-like stuff into science stuff from Tom Scott...I'm loving it!

That’s what I’m working on currently for my masters. It’s a difficult line of research due to how much of it isn’t public knowledge.

It's amazing that we can understand so much about nature, yet be eluded by such basic things. Another example of this is the dynamics of a 2 wheeled vehicle such as a bicycle or motorcycle.

Tom trying out being one of the slow mo guys

Now *THIS* is the kind of science I can get behind!

2:15 Kinda cool to see 3D printed tooling used in an application like this! With heat set threaded inserts even

Great video Tom - but please for goodness sake get the slow mo guys there with a phantom camera! They did an amazing video with an explosion where you could clearly see the shockwave, initial blast wave and negative wave pressure.

Reminds me of the shock waves reflected by the ground during air bursts of nuclear weapons (albeit on a much larger scale), which then interfere constructively and largely increase the force of the blast.

I like that the guys setting up the tennis ball sized piece of c4 are wearing earmuffs and safety glasses.

Awesome work Tom! as always!!!

i genuinely feel like insights in this research can be changing the future of humanity, control over the force exerted at that precise a scale lets us make new engines, reactors, materials

That's true! I'm an FX artist and the start of the simulation is pretty weird, it looks cool because it's the magic of the cinema, it's based on real life but the actual application is very weird indeed lol

This is the most Slow Mo Guys video Tom Scott has ever done.

The access statistics of the paper show clearly when tom uploaded.

I turned the volume up and started paying more attention at "...could save lives" and it immediately made me feel like a big utilitarian nerd instead of a just a vague general nerd.

Have you ever covered how factories stitch books with thread? I'm trying to get my brain around it and just can't. I haven't found any videos that go into how it works, at least not as well or detailed or complete as some do for fabric sewing.

"We don't know what we don't know" - Sun Tzu, The Art of War

Congratulations on 6m subs Tom, still going strong after all this time ❤.

Cool guys look away from explosions, cooler guys look AT the explosions.

I used to work with a group of people who designed warheads, like HB 876 (I knew the guy who suggested the dimpled case) and BL 755. When I was paying attention they were modelling self forging fragments, which involved modelling the detonation of explosives and the forming of the metal plate that they were in contact with. Their experimental results corresponded very well with their model. So I'm surprised to hear, nearly 30 years later, that they didn't understand the explosion. It seemed like they understood it really well. This short range blast was actually far outside of their area of interest, by the time the plate started to move the explosion was discarded from calculations and the metal was just coasting to its final configuration (teardrop shape, pointy end first) and had already reached its maximum velocity.

"A whacking big steel plate..." love it!

That was absolutely fascinating and possibly the most interesting vid I’ve watched this year.

Dr Sam seems like a fun guy to chat to about explosions

It's interesting how a slow-mo real explosion looks a lot like a movie one :-) turns out they were really onto something, haha!

FASCINATING stuff, the possibilities are astounding of this kind of understanding

Another great Tom Scott video!

This is the kind of thing I thought people would have figured out by now. It’s crazy how much we still don’t know about the world

I absolutely love watching you. so informational. I just set you up on my second monitor and work on my primary.. Keeps me entertained all day! Thank you!

Thanks Tom, that was brilliant, my coffee nearly went cold. Cheers

Imagine meassuring blasts. That job must be a blast

Can we all appreciate how much a wonder nerd Tom is. He is all of us there

I thought this was an old episode replayed. Thank you and a have a great day.

That was fascinating. Thanks to the reasearch team for showing us

This team needs to hit up the slow mo guys

5:05 if you pause frame by frame you can see that the light from the explosion shows up on the ground faster than the camera can catch the light emitting from the actual explosive.

That is a VERY satisfying explosion noise

if I am not mistaken it's taught in the military to stay clear of walls during explosions exactly because of this double pressure from the blast and the bounce.

I bet this'll be a banger.

how awesome would it be to say you study explosions for a living

These dudes blow things up in slow motion for a living. That's definitely cool.

It does make sense why it would be so "difficult" to measure and understand a concept so important to nuclear weapons.

that's cool to see! thanks tom, nice slow motion explosion up close.

The slomo guys do this and have had some amazing results with reignited gasses from the pressure wave

did load of work on that site years ago where they were testing new gas pipeline systems. weeks wiring up strain gages and thousands of meters of cables back to the control building.

We haven't figured explosions out? I am blown away!

If you film yourself being very, very close to an explosion for TikTok, you’ll soon be everywhere.

Hi Tom big fan been watching since the young times. Never die please

tom i want you to know that i love your podcast lateral and will be absolutely crushed if it ever goes away, mentioning it here, because i didn't know it existed until recently.

Interesting stuff. I'll be sure to check out the paper you linked in the description.

I didn't know this was a mystery. I always assumed other people could sense the blast wave rebounds. Very interesting.

Surprised that areas like understanding nuclear explosions haven’t helped in knowing other means such as this.

This little thing looked way more powerful than what we got for the explosion in Oppenheimer.

Congratulations on the 6 million subscribers.. 5.99 .. almost there

To be honest if your 5cm away from a large explosion I would say you have no problems 😂