Engagement Talks

Here you will find three engagement talks (videos of approx. 10 mins) that cover very different areas of maths and physics.

If you would like to ask any of the speakers a question or even just comment on their talk then please type this in to the box below their talk and we will send it directly to them. Their responses will be uploaded here in early August and we will email you to let you know.

Click the talk titles below to start watching.

The Skeleton of Our Universe

Your questions answered by Cora in 2020.

Thank you for your interest and the great questions. Asking questions is really what science is all about! Many of your questions have only been answered recently or are still an active area of research."

"Do you think we will we ever be able to develop telescopes powerful enough to record videos that are practically in real-time?“ (anonymous)

We already have very powerful telescopes that can track individual objects and events with a good time resolution. Many of the telescopes used to map the large-scale structure are simultaneously being used to study rare and variable objects. Observing the cosmic web as a whole in real time wouldn’t look all that interesting, because it takes quite a while for large structures to form. When observing the cosmic web with telescopes, we actually do something extraordinary, we simultaneously record different times at once. But then scanning a large area of the sky is the part that really takes time. The challenge for large galaxy surveys is to find the right balance between finding many distant and dim galaxies (a deep survey) and covering a large area (a wide survey) to get a good idea of the large-scale structure.

"If the galaxy continued to expand, would it ever expand so extensively that it collided with another galaxy? If so, what happens then?“ (anonymous)

The galaxies themselves actually do not expand, just the distance between them. This is because galaxies, like our Milky Way, are bound objects, so the gravitational forces hold them together and effectively shield them from the expansion. So a very extensive expansion of the universe would mean that most galaxies get further and further apart from each other. But the gravitational pull in bound systems can cause galaxies to collide with each other. This is a common process in galaxy evolution and can lead to a merger of two galaxies into one. We actually expect one of those mergers to occur in our our local group of galaxies. (see the answer below)

"Thank you for giving up your time to do that talk - it was so interesting! I was curious to ask about the cosmic web. I'd like to know a bit more about what it is that causes some galaxies to move away from us and some to move towards us." (Cora A)

This is question connects very well to the previous one. Broadly speaking, most distant galaxies move away from each other as the universe expands. But galaxies that are gravitationally bound within a larger system do not behave like this, instead they are being pulled by gravitational forces that are much stronger than the overall expansion. Our Milky Way and Andromeda are part of the local group of galaxies, which is part of the even larger Virgo supercluster of galaxies. Within the local group, the Andromeda galaxy is slowly approaching the Milky Way and a collision is expected to happen in about 4 billion years. (See this nice NASA article with a video: https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html) And our whole local group is being pulled towards the centre of the Virgo supercluster.

"Also, do we have records of other planets experiencing this kind of shift with other stars.etc and if not, do we aspire to investigate this deeper in the future?" (Cora A)

Stars can also collide and merge, and those events can be of great interest for cosmology. One example is a certain kind of supernova that occurs when a white dwarf and another star orbit each other closely, which can set off a large stellar explosion. Those so-called Type Ia supernovae are extremely bright and have a very characteristic profile of light, such that we can use them as „standard candles“ to measure distances. In 1998, scientists analysed observations of distant Type Ia supernovae and found that the universe was expanding at an accelerated rate. This observation caused a real paradigm shift and multiple upcoming large galaxy surveys are aimed at finding out what drives this accelerated expansion.

The Reality of Imaginary Numbers

Your questions answered by Matina in 2020.

”Please could you explain in more detail how complex numbers are used in circuits?” (anonymous)

An AC circuit can be described by the voltage \(V\) (Volts), the current \(I\) (Amps) and the impedance \(Z\) (Ohms). Voltage measures the energy that a charge gets when it moves between two points, an electric current is the rate of flow of charge past a point and impedance measures the opposition of an electrical circuit to the flow of electricity when voltage is applied. We represent the impedance as a complex number and Ohm’s Law becomes \[V = IZ.\]

For example, if the circuit has a current \(I = 4 + 2i\) and an impedance \(Z = 1 - i\), then \[\begin{align}V & = (4 + 2i)(1 - i) \\ & = 4 - 4i + 2i - 2i^2 \\ & = 4 - 4i + 2i + 2 \\ & = 6 − 2i.\end{align}\]

Further notes: In a series circuit, the impedance is the sum of the impedances for the individual circuit components. In a parallel circuit, there are several paths through which the current can flow. If we have two impedances \(Z_1\) and \(Z_2\) connected in parallel, then the total impedance is given by \[Z_t = \frac{Z_1Z_2}{Z_1 + Z_2}.\]

We also note that complex numbers are used to analyse DC circuits.