The Microbiome Fleur Masters

The first postulate is one that seems quite intuitive. The only interesting idea it challenges is that if the rules of physics are the same for all inertial observers, then all inertial frames are as relevant as each other. However, the second postulate is a bizarre claim. If we were to pretend that this result was the same for all particles, then if a stationary observer measured the velocity of a car to be 50mph, an observer travelling at 20mph would also measure the exact same car to be travelling at 50mph. Of course, in reality, this moving observer would measure the car’s velocity as 30mph. Yet this second postulate has been experimentally proven countless times. Perhaps unsurprisingly this causes some bizarre phenomena.

LENGTH CONTRACTION & TIME DILATION

These two effects arise because of the constancy of c, the speed of light. Einstein carried out a series of thought experiments when composing his theory. One of which described a photon clock being seen by two observers moving relative to one another. The clock consisted of a photon being reflected off two mirrors. Each time the photon hit a mirror the clock ticked.

Now suppose the clock begins to move at a constant velocity. To a stationary observer, we may see that the photon appears to take a path like:

We can see that the stationary observer sees the clock tick slower than an observer who would be travelling with the clock or relative to a local clock. If we wanted to calculate the exact difference in time, we can say that for one tick: The primed values are used to show measurements taken from the stationary observer. For example, d’ is the distance travelled by the photon measured by the stationary observer. v is the relative velocity of the photon clock and t’ is the time taken for the photon to hit the photon clock. Using Pythagoras:

is known as the Lorentz gamma and is the main tool in special relativity that shows how to convert time and distances between observers. Not only is time dilated by this factor, but lengths are also contracted by this factor in the direction of motion to maintain the spacetime interval.

THE TWIN PARADOX

The most famous paradox of Special Relativity is the twin paradox. In this paradox there are two twins, one travels to a star 3 light-years away at near lightspeeds whilst the other remains at the earth. Both twins see each other’s clocks run slowly compared to their local clocks, so when they reunite, who is older? The answer can be seen clearly using a spacetime diagram. On this diagram, the twin on earth has coordinate axes x’ and t’ and because the x’ axis is in light-years, a photon beam will always sit at 45° to the horizontal. To represent the twin moving away from us we can draw a line at an angle to the vertical. Here, the twin reaches the planet after 3 earth years and heads back to earth. Due to the twin on earth being stationary their worldline is straight up. The stationary twin’s worldline is just the same as its time axis and we can say the same for the moving twin. The twin’s position axis is hence at the same angle to the horizontal because the photon worldline must run at the same angle to both t and x axes.

Much like how the x’ axis represents the stationary twin’s present time, the x axis shows the moving twin’s present. However, after reaching the star and turning back towards earth, the frame of reference of the twin changes and so does his x axis. If we were to see how many of the stationary twin’s birthdays the moving twin experiences we see that he doesn’t experience some birthdays as he returns home.

The twin that travels to the star experiences less time than the stationary twin. Or in more conventional terms, accelerating frames of reference age less than stationary frames of reference.

THE LADDER PARADOX

This paradox states that there is a barn that is just too small to fit a ladder into it. The ladder is then sent through the barn at a fraction of the speed of light so that it is length contracted just enough to close the barn doors with the ladder inside. From a stationary observer, the ladder is completely locked in the barn, yet from the perspective of the ladder, the ladder is still unable to fit into the barn. How can the ladder be both in and out of the barn at the same time? The answer can once again be found in the form of a spacetime diagram. Firstly, a spacetime diagram from the stationary perspective. The gaps in the barn worldline represent the times the doors of the barn are open.

Yet we can add present time lines from the perspective of the ladder or the ladder’s x axis. We see the ladder views itself as far longer than the stationary person does as we would excpect and we also see that the ladder doesn’t even view the gates shutting as simultaneous events.

So does the ladder fit in the barn? Well, yes and no. Its all a matter of perspective. This also shows how simultaneity, and even sometimes orders of events, is relative.

Lower Sixth Talks

The Catecholamines

The Invisible Forces - Aerodynamics

Isabel Singleton

I first came across the catecholamines when researching the body’s response to threats. Here, I discovered this group of monoamine neurotransmitters’ role in the fight-or-flight response. It has always amazed me how something so seemingly small accounts for such urgent responses, and I found myself instantly drawn to their biosynthesis and functions. Further reading brought me to pheochromocytoma, a fascinating catecholamine-secreting tumour, which, in turn, led me to metanephrine and catecholamine degradation.

Before the stride of the Wright Brothers in the early 1900s, flying had seemed to be an impossible task, only coming true in fairy tales. Who could have anticipated thousands of airliners, each carrying hundreds of passengers across the globe daily only a century later? Like many others, I have been fascinated by the science of flight and to put it in academic terms, aerodynamics, which explains not only the theory of flight but is also applied to wind turbines, race cars, sailboats, buildings (and the list goes on!)

O-Teen Kwok

Brain-Computer Interface

Chelsea Chen

I have always been fascinated by neuroscience and its application in medicine. Inspired by one of the MIT neuroscience open courses which discusses brain-computer interface (BCI), I gained interest in what connecting the brain and computer can achieve. For paralysed patients with an interrupted brain-spinal cord-muscle pathway, BCI can act as an external conductor of their brain signals, thereby enabling movement and communication just by the thought of it. My journey of research was eye-opening as it is incredibly exciting to see the bright future of neurotechnology through BCI..

Quantum Computing

Alex Mylet

I chose to talk about quantum computing because I had seen articles announcing new milestones and developments in quantum computers, both advances in qubit numbers and error correction techniques. However, I found that many of these articles required a deep understanding of quantum mechanics and quantum computing to properly understand, so I decided to gain a basic understanding of quantum computing and then continue to read deeper.

Tumour Dynamics

Ryan Li

Cancer is complicated, making it that much more challenging to cure, despite advances in medical technology. Science’s persistent attempt to shut off what is otherwise arguably the most successful DNA reproducing machinery in evolutionary history is ongoing. The reasons for cancer recurrence are numerous, which led me down a surprising route in investigating one of the most likely and intriguing aspects of cancer tumours - heterogeneity.

The Catecholamines

Isabel Singleton

As the name suggests, the catecholamines are made up of a catechol (C6H4(OH)2) and an amine group (-NH2), making them monamine neurotransmitters. They include dopamine, norepinephrine and epinephrine. Dopamine is produced by neurones in the midbrain. Both norepinephrine and epinephrine are produced by chromaffin cells in the adrenal glands and in the sympathetic nervous system.

DOPAMINE

Dopamine’s role in the body changes depending on the dopaminergic pathway. In the nigrostriatal pathway, dopamine affects the basal ganglia’s regulation of movement. Too little dopamine in this pathway establishes the link to Parkinson’s disease. The mesocorticolimbic pathway joins the mesocortical pathway (VMA in the midbrain to the prefrontal cortex) and the mesolimbic pathway (prefrontal cortex to nucleus accumbens). It is this pathway that has been nicknamed ‘the reward pathway’ as it has an effect on mood, with an increase in dopamine leading to a sense of euphoria or even hallucinations. The final pathway is tuberoinfundibular, which is dopamine’s endocrine pathway. When there is less dopamine here, the periventricular nucleus in the hypothalamus signals the pituitary gland to secrete prolactin. This is why dopamine is sometimes referred to as the prolactin inhibiting factor.

NOREPINEPHRINE & EPINEPHRINE

Norepinephrine and epinephrine work together to carry out the fight or flight response. Their main difference is that epinephrine works on both alpha- and beta-receptors, whereas norepinephrine only works on alpha-receptors. Alpha-receptors are only found in the arteries and have a particular affinity for norepinephrine, which accounts for the vasoconstriction that occurs during the stress response. Epinephrine increases blood sugar levels (by stimulating glycogenolysis in the liver) and heart rate. It also relaxes the smooth muscles of the bronchiole, making it easier to breathe (this is why epinephrine is the preferred treatment for anaphylaxis).

BIOSYNTHESIS

The catecholamines are derived from the amino acid tyrosine. The initial step of catecholamine biosynthesis is when tyrosine is hydroxylated to dihydroxyphenylalanine (DOPA) via an aromatic amino acid hydroxylase (AAAH) called tyrosine hydroxylase. In turn, DOPA is decarboxylated (via aromatic amino acid decarboxylase) to form dopamine. In neurones that use dopamine as a neurotransmitter, this is the final stage of enzymatic modifications.

For neurones that use norepinephrine, dopamine is hydroxylated by dopamine-beta-hydroxylase (DBH). Norepinephrine is then methylated by phenylethanolamine-N-methyltransferase (PNMT) in neurones that use epinephrine as a neurotransmitter. This uses the cofactor s-adenosyl methionine (SAM), which donates a methyl group.