I didn't expect you to! 🙄
I simply thought that attempting to compress an entire physics curriculum into an 8 minute video was a bold feat.
To help understand emergent spacetime, here is an analogy:
If we dissected a fish into all its constituent parts such as muscles and bones we could understand the dynamics of how a fish swims, but we would not be able to explain all of fish behaviour, e.g., the way that fish swim in schools.
To explain this behaviour it would be best to view a school of fish as a new organism because it behaves differently from the dynamics of any individual fish.
The school can then be described as a macroscopic property that emerges in some, not so obvious, way from the microscopic theory of fish dynamics.
Similarly with spacetime:
Some theorists believe that spacetime (and the notion of particles and fields within it) is a property that emerges from the dynamics of some other underlying microscopic theory, and that this underlying theory must be quantum mechanical in nature.
This means that at some scale the notion of a smooth spacetime has to break down. This is thought to happen at smaller scales and higher energies than are currently being probed by particle accelerators.
I have adapted and expanded information from this 10 page pdf : https://guava.physics.uiuc.edu/~nigel/courses/569/Essays_Spring2018/Files/gupta.pdf
Last edited:
If time was quantized, space time would surely also be quantized?
You can only resolve a particles position or velocity down to a certain level and you always have to trade position or velocity accuracy the finer the required accuracy. That seems to tell me time must be quantized. Further, EMR does not extend to infinite frequency, so resolution will always be limited by that fact anyway.
You can only resolve a particles position or velocity down to a certain level and you always have to trade position or velocity accuracy the finer the required accuracy. That seems to tell me time must be quantized. Further, EMR does not extend to infinite frequency, so resolution will always be limited by that fact anyway.
Gamma rays get a mention of sub atomic wavelengths, I wondered if there was record for how short, This popped up
https://www.eurekalert.org/news-releases/1003672
Scientists using the H.E.S.S. observatory in Namibia have detected the highest energy gamma rays ever from a dead star called a pulsar. The energy of these gamma rays clocked in at 20 tera-electronvolts, or about ten trillion times the energy of visible light. This observation is hard to reconcile with the theory of the production of such pulsed gamma rays, as the international team reports in the journal Nature Astronomy.
Also this one
In a 18 May 2021 press release, China's Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a dozen ultra-high-energy gamma rays with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV), including one at 1.4 PeV, the highest energy photon ever observed.
There are a number of Planck units
https://en.wikipedia.org/wiki/Planck_units#Derived_units
These are exceptional energies, but they are still quantized. I'm thinking about the ultraviolet catastrophe that kicked this whole QM thing off!
Although time is not quantised in the general theory of relativity and in quantum mechanics, some physicists think it may be when these are combined to produce a theory of quantum gravity.
Here is what some prominent theorists have to say about the quantisation of time: https://www.scientificamerican.com/article/is-time-quantized-in-othe/
One contributor even suggests that time, like space, is three dimensional!
I read that Planck time may not be a quantisation of time itself since there is no requirement that the time between two events be separated by a discrete number of Planck times. https://en.wikipedia.org/wiki/Chronon
I do wonder sometimes if, in formulating the concept of space-time, Minkowski and later Einstein, saw a path to describing GR with the field equations that explained a simultaneous effect on both dimensions. So Einstein saw that spacetime was curved, and then developed the field equations to describe that very accurately. Could you separate space and time out, and invoking c as the cosmic ruler so space and time are one and the same, just focus on time as the thing that makes space appear to curve and, where time is slowed down due to the energy contained within local matter, make it appear to have mass in conjunction with the Higgs field?
This is not questioning GR's predictions for both dimensions, which we know are exceedingly accurate, but is asking something about the underlying mechanism.
Yes, the idea that space and time could be quantised goes way back to Heisenberg's Uncertainty Principle.
However, Ethan Seigel says, "Sure, everything is quantum, but not everything is discrete".
https://www.forbes.com/sites/starts...ce-and-time-quantized-maybe-not-says-science/
Ethan says that Heisenberg realised that certain quantities went to infinity, when you tried to calculate them in quantum field theory.
This led Heisenberg to postulate that if there was a minimum distance scale to space then these infinities would go away.
Other than being a convenience how do we know time is real? Yes, I realize we can measure it but we invented the clock. hours, minutes, seconds, pico seconds, they are all arbitrary, no?
Not in general relativity where time and space are inextricably combined to form an entity that is distorted by matter and energy.
However, space and time could be separated at very high energies, such as those found in the early universe when quantum gravity ruled.
Perhaps general relativity emerges from quantum gravity at low energies?
Our measurement units are arbitrary, but they can be used to explain accurately the rate at which things happen and we can make predictions. There are a few universal constants that aliens no doubt also know about, but probably express them in ways we would not understand, and vice-versa.
Galu, if you teased time and space apart and looked at them separately, I guess you'd have to call it something else, but I'm certainly not going to challenge Einstein!
I think the quantities ballooning to infinity was probably a mathematical result that, as Heisenberg must have realized, could and did not reflect reality. GR field equations break down at infinitesimal distances, so there is a clear disconnect there as well and that is why I wondered if space and time were teased apart, you could deal with time as a quantized dimension, and then recombine them. While they are inextricably treated as one, there is no opportunity to do this.
You have to ask if it is not possible to measure position and velocity simultaneously below a certain resolution, then is time, like energy, quantized? This must in turn lead to a discussion about EMR (photons) (which will have an upper energy limit aka frequency) which we know is quantized. How are they ultimately linked is the question?
Sometimes QM does seem to fit in with relativity 😉 not that I want the maths needed to grasp that.
https://en.wikipedia.org/wiki/Dirac_equation
That link leads to others which in turn may well lead to more. White holes, black holes. Hawkin's radiation - seems he made a mistake and lo another radiations crops up. Afraid I see QM as useful science fiction. It can predict but in practical terms has little relationship to physically realisable devices that use what could be called it's usage.
https://en.wikipedia.org/wiki/Dirac_equation
That link leads to others which in turn may well lead to more. White holes, black holes. Hawkin's radiation - seems he made a mistake and lo another radiations crops up. Afraid I see QM as useful science fiction. It can predict but in practical terms has little relationship to physically realisable devices that use what could be called it's usage.
In the formulation of spacetime, c was introduced to define how to compute distance in the time direction.
When we speak of "distance in the time direction", we are treating time as an additional dimension in space.
The distance between spacetime events is calculated using coordinates (x, y, z, ct), where c is the speed of light.
Note that ct has units of length, just like x, y, and z. Consequently, time may be regarded as a spacetime distance.
Even if you don't change your spatial coordinates x,y and z you will still travel from one location in spacetime to another, and do so at the speed of light!
Allow me to flesh that out a little.
Schrödinger’s wave equation works fine when describing an electron in a light atom where it orbits at much less than the speed of light.
However, an electron in a heavier atom is whirled around at close to the cosmic speed limit and Schrödinger’s equation breaks down.
Dirac, pictured above, came up with an equation describing the electron that was compatible with the special theory of relativity.
From Dirac's equation emerged the concept of 'spin', which is an intrinsic quantum property with no analogue in the everyday world, and a prediction of the existence of 'antimatter'.
More here: https://www.livescience.com/physics...tics-how-paul-dirac-found-his-famous-equation
You could I think just as well replace distance coords with time. If space is curved and matter has to follow the curvature, would that manifest as longer transit times ie so light bending around a massive object takes a longer path compared to the direct route if space was not curved?
Don’t you think semiconductors is a good practical application of QM? Just asking because I always assumed when you are working at the atomic level, electric fields, photons etc in that branch of engineering, it was firmly resting on QM.
What about quantum tunneling? That's something which was first predicted by quantum mechanics and then found to have a real life application.
Applications include Scanning Tunneling Microscopy, Tunnel Diodes and Josephson Junctions (discussed earlier in the thread).
However, would that be compatible with the formulation of spacetime?
Do you mean will the light take a longer path in time compared to the direct route?
Let's think of the light as a straight line drawn on a sheet of paper.
If the paper is then curved the line is no longer straight, yet the line itself hasn't deviated from its path.
Consequently, if light doesn't actually deviate from its path through curved space, might its transit time be unaffected by said curvature?
What say you? I'm just a cosmology geek? 🤓