I remember being an undergraduate.  And at about the time the image above was captured, I recall imagining being very tiny – smaller than an atom – and moving through the atoms of ‘my body’. I remember asking: How would I identify the edge of ‘me’?

On this tiny scale, the nuclei of atoms would be far apart, and so I would barely be able to tell whether I was inside an atom, or in-between atoms. The edge of ‘me’ would be very hard to detect: it would correspond to nothing more than a relative decrease in the frequency with which I came across a nucleus. And also to changes in the types of nucleus I encountered – with many fewer carbon nuclei in the bits that were not ‘me’.

The upshot of my imaginings was that I decided that the concept of an ‘individual’ was one that only made sense when viewed on a large scale. On a small scale, all one would see would be essentially chaotic variations. This was a pivotal moment for me,

From this journey of my imagination I understood (pace any high energy physicists out there) that in same way that a microscopic explorer would never deduce the existence of the phenomenon I called ‘me’, so looking at the components of matter would never – even in principle – result in a ‘theory of everything‘.

I was reminded of this insight today while reading an article in the Scientific American on bacteria. First I was shocked to find that: In the human body, bacterial cells outnumber human cells 10 to one. The article then explained that many dis-eases were not caused by ‘foreign’ bacteria, as had at first been imagined. Instead many dis-eases arose from a disturbance of the ”social’ balance between the vast populations of bacteria that live on (and within) our bodies.

For example, the microbe Heliobacter Pylori is associated with ‘causing’ stomach ulcers, but in normal life Heliobacter Pylori lives happily in our stomach. And it helps us by producing the hormone ‘ghrelin‘ which produces a sensation of ‘satiation’ after eating. Similarly, the bacterium Bacteriodes fragilis stops inflammatory T cells from damaging our bodies, and ts absence could be associated with auto-immune diseases.

And so biology brought me back to same question that physics had raised 30 years ago. What do I mean when I use the word ‘I’? Physics told me that ‘I’ was only blearily separated from the atoms around ‘me’. And now biology tells me that ‘I’ am a combination of my genetically unique cells, and a vast army of bacterial ‘hangers on’ that have come to live with ‘me’ essentially by chance.

The concept that dis-eases were not caused by individual poisonous foreigners, but instead resulted from an imbalance in a diverse social network resonated strongly with me. And so I thought I would share that with you. Goodnight.

Further reading. This entry was originally posted on Michael’s blog.

Through photosynthesis, do plants take light energy from the Sun, convert it into mass and actually add to the overall mass of the Earth?

The person who asked this question is probably referring to Einstein’s famous equation E=mc². However, plants are no particle physicists and cannot convert energy into mass. What they can do better than any human chemist though, is to capture the energy contained in sunlight and use this to combine two of the most abundant compounds on earth, carbon dioxide and water, into glucose.

Glucose, or fruit sugar as it is also known, is used by living creatures ranging from yeast to elephants as a carrier of readily available energy. The only ones that can actually make it from scratch (or rather CO2 and H2O) are plants, however.

To do this, they need energy and a catalyst, because these two compounds don’t spontaneously combine to form glucose, as everyone who has ever drunk a glass of sparkling water knows. The two partners need to be coaxed together, and get ‘excited enough’ before they will form a more permanent bond. The matchmaker in this case is called chlorophyl.

Chlorophyl is the substance that gives all leaves their green colour. It is a protein which is able to capture the energy contained in sunlight, and use this to ‘excite’ CO2 and H2O to such a level that they are willing to combine into a new substance called glucose. The actual equasion describing this chemical reaction is depicted on our homepage.

The important thing to note here is that glucose becomes a ‘carrier’ of the energy that was used in its creation. When you run up the stairs and ‘burn’ glucose in your muscles by combining it with oxygen, this is just a way to release this energy to power your muscle cells, and the glucose is reverted back to the CO2 and H2O it was made out of by a crafty plant. When you stand panting on top of the stairs, you are releasing them back into the world, where they will be ready for absorption by another plant to start the whole cycle again.

So, in conclusion, no mass is being created by plants, they just temporarily capture energy into mass.

Asked by Liam, from Fleetwood

Trigger: We believe that triggers for the ice ages and interglacial warming periods are small changes in the attitude of the Earth in its annual journey around the Sun. These ‘orbital wobbles’ are small and barely alter the average amount of energy reaching the Earth. But they do alter day length and summer length at high latitudes. Imagine what happens at the ‘snow line’ – the line of latitude at which snow just lies on the ground over summer. If summer lengthens or intensifies then this can cause snow to melt, which changes the albedo of the surface – making it darker and increases the rate of warming. Orbital changes trigger this kind of change.

Driver: When the Earth warms up microbes wake up and digest biological matter in the Earth and release methane (CH4) which reacts after about 10 years to make CO2 which stays in the atmosphere for hundreds of years – causing more warming and making the release of further CO2 more likely. So the ice core record shows changes in CO2 that correlate with ice ages. But these did not trigger the ice ages or interglacial periods. However, the changes in CO2 concentrations did drive the changes once they began.

Scientifically, ‘colourfulness’ scales how colourful something is. Zero colourfulness things include white, grey and black. Though the ‘neutrality’ of whites and greys is rather tricky – often the most neutral thing visible wil be judged as being neutral, so it’s a self calibrating relative white point thing rather than an absolute.

In as much as there are many ‘acceptable’ whites, there’s a volume (was colour is a 3D thing) of colours one could describe as black, with the blackest black being the one which emits or reflects no light at all, and a purist might say that’s the only black the original question was all about. Then we’re at the hub of this perceptual and philosophical territory.

Looking at analogues with other senses and logic, is total silence a sound? Is zero a number? Your answer lies somewhere between these two.

 About our guest scientist

Jonathan Bergmann is a teacher, educational coach and writer from Illinois, USA. You can find out more about Jon on his personal website, or on twitter. This video was created by Cognitive Media for Ted Education.

Oh, you might be thinking – not so serious then; a change from 8.2 to 8.1 isn’t much of a change. Sadly, it is serious: it corresponds to a 25% increase in the number of ‘acid molecules’. So let me explain the pH scale, one of the worst-designed and poorly-named scales in science.

The ‘H’ in pH stands for Hydrogen, and scale seeks to measure the concentration of hydrogen ions in a solution. A hydrogen ion is a hydrogen atom which has had its electron removed. Its symbol is H⁺ and it consists of a single fundamental particle – a proton. It is uniquely mobile and reactive and the entire chemistry of acids and bases is all about the behaviour of this ion.

I had always wondered what the ‘p’ stood for in pH andWikipedia tells me that I am not the only one to wonder – its actual meaning has been lost in the mists of time! Originally it may have stood for ‘power’ or ‘potential’.

However rather than just recording the number of ions per unit volume, the scale seeks to make things ‘simpler’. Don’t you just hate that!

• In nominally pure water, at around room temperature there are around 0.000 000 1 (or 10^-7) hydrogen ions for every water molecule – roughly 1 H⁺ ion for every 10 million water molecules. The pH scale calls the acidity of pure water 7.
• In seawater there used to be roughly one hydrogen ion for every 158 million water molecules, or equivalently 0.000 000 0063  (6.3 x 10^-9) hydrogen ions for every water molecule. Using fancy maths it turns out that 6.3 x 10^-9 = 10^-8.2 and so the pH scale says seawater had a pH of 8.2
• In seawater now there is roughly one hydrogen ion for every 126 million water molecules i.e. the concentration has increased by around 25% . Equivalently there are now 0.000 000 0079 (or 7.9  x 10^-9) hydrogen ions for every water molecule. Using fancy maths one can show that  7.9 x 10^-9 = 10^-8.1 a and so the pH scale says this seawater has a pH of 8.1

This 25% increase in ocean acidity is a direct results of the roughly 30% increase in atmospheric CO2. The way in which dissolved carbon dioxide causes water molecules to dissociate more than they otherwise would is complicated – so complicated that it is called Chemistry :-). But trust me: it does.

The acidification is what makes fizzy drinks taste interesting, but what is good news for sparkling water aficionados is bad news for the many kinds of organisms that live in the sea and which form the base of the food chain that sustains the ecosystems of the oceans. Animals that have shells will find it especially hard to cope if CO2 levels continue to increase. This BBC story describes research near underwater volcanos which shows how ecosystems are affected by increased acidity.

Please note: it is all much more complicated than I have made out! Ocean acidity varies from one part of the oceans to another and with depth and … well, there are many factors in play.  But very roughly the pH of mid-ocean sea water has decreased from around 8.2 to around 8.1  and the decrease will continue if atmospheric levels continue to rise.

Originally posted on Michael’s Protons for Breakfast website.

About our guest scientst

Mark is a journalist, author and medical historian. Specialising in the science and history of infectious disease who’s work appears in the Guardian, the Observer and the Lancet. You can find out more about Mark on his website, or contact him via twitter @honigsbaum.

This video was originally posted at Ted Education.

You might have thrown snow balls as a child. Thinking back to those days, when you collect some snow from the ground it’s nice and fluffy and soft. This is because snow is made up of lots and lots of tiny ice crystals that have a lot of space for air to get trapped inside.

Once you start rolling and compressing your snow ball, it will get progressively harder. Keep pressing long and hard enough and the snow ball will have turned into an ice ball (the ones that the nasty big kids throw at you). This is because you have pressed out all the air that was trapped inside the snow crystals, and the ice crystals have been compacted together into a block of ice!

Find out more at SnowCrystals.com

Asked by Aamir Hassan, Peterborough

First assume that the cereal is made up completely of carbon. 12 grams of carbon contains approximately 6.023 x 10²³ atoms of carbon (The Avogadro Number from earlier on).  So 200 grams of carbon contains (200/12) ~ 17 x 6.023 x 10²³ atoms. Each atom of carbon contains 6 electrons. So the final total is 6 x 17 x 6.023 x 10²³ which comes to 6.14 x 10²⁵ atoms.

Next assume that the milk is made up completely of water. 18 grams of water contains approximately 6.023 x 10²³ molecules of water (The Avogadro Number again). So 200 grams of water contains (200/18) ~ 11 x 6.023 x 10²³ atoms. Each molecule of water contains 2 atoms of hydrogen each with 1 electron and 1 atom of oxygen each with 8 electrons which makes 10 electrons per molecule. . So the final total is 10 x 11 x 6.023 x 10²³ which comes to 6.63 x 10²⁵

These two numbers are so similar that it barely makes any difference what we assume – so 400 g of cereal – made up of any mix of milk/cereal contains roughly 6.14 x 10²⁵ + 6.63 x 10²⁵ ~ 1.27 x 10²⁶ electrons.

And pretty much exactly the same number of protons.