“It can be difficult to have an idea of the enormity of the scales involved …”
Scientific photo library / Alamy
Most of us can relate to the concern of inflation: we are all concerned with the cost of living and what our political leaders do to remedy it. Sometimes I have to remember that we have a bit of a nomenclature problem in physics, because inflation means something completely different for us.
Cosmic inflation is a model that explains why our universe resembles the largest scale. In this scenario, space-time quickly spread for a tiny fraction of a second. This means that parts of the universe which would currently have no way of being in contact with each other could have been in the past.
It can be difficult to have an idea of the enormity of the scales involved. How can we be so confident that we even understand these distances, which are far beyond our daily sensitivities? In the chronicle last month, I addressed this question by explaining how we measure the distances. But the questions have their own type of inflation: answering this riddle has more (well!) Questions.
In this column, I explained that an important tool to measure cosmic distance is a phenomenon called Redshift. Think of a ball with corrugated lines. Imagine now that the ball is exploded. The scribbles extend, with the length of the peaks and valleys that grow longer. This is what happens to light when it moves over the entire length of space-time. The light extends and the wavelength lengthens – and therefore more red, hence the name.
This stretch of light helps us measure the distances. We calculate the wavelength of the light that we expect to see from distant objects and compare this with what we really measure. The difference between the two tells us how the space-time has extended between us and the object that we examine. This, in turn, allows us to estimate the distance. Red difference measurements have been validated repeatedly by astronomical observations and laboratory experiences.
But a question hides in the background. From the point of view of quantum physics, the wavelength of light corresponds to the amount of energy of light. The more light, the more light, more energetic. This means that when the light is shifted in red, it turns into light on the lower energy. At first glance, it is not really annoying, just a cool characteristic of quantum science in conversation with cosmology.
Energy conservation is the rule of daily physics, but even the cosmic rules are sometimes folded or broken
The problem? We like our physique to be consistent with other physics. And one of the principles of daily physics is the conservation of energy, the idea that energy cannot be created or destroyed, simply transformed. So, if we assume that the conservation of energy applies to the light offset to red, this invites the question: what is going on to the lost energy of light? A clever reader asked me this very question.
The answer may be surprising: energy conservation is the rule, but even the cosmic rules are sometimes folded or broken. In the case of cosmic distances, the rule governing is the theory of general relativity of Albert Einstein. This concept, which is most famous for the introduction of the idea of space-time with Courbure, is also the reason why we can show mathematically that it is possible for space-time to develop.
Another characteristic of general relativity is that the energy is not preserved. In other words, when the light loses energy during its offbeat towards red, the theory says that it does not really matter. Energy should not go somewhere. It can simply disappear.
At least, it’s a way to talk about it. Alternatively, we must take into account not only the energy of light, but also from the energy associated with gravity – with the quantity of curvature in space -time. Over the years, these two apparently divergent ways to think of the situation have caused a lot of problems. There are real disagreements on the most legitimate description. There are also those who see them as two sides of the same medal.
My personal point of view is that it comes back to what energy is. Although energy is difficult to define, we can have an idea of what it is and where it is due to material objects such as particles or stars. But once we say “the curvature of space-time has an energy associated with it”, things become troubles. Where is energy? Everywhere in space-time? How much of this energy is at some point? And so on. This is the inflation of questions!
So I am inclined to agree with people who say that energy conservation is not a useful concept here. What we can say with confidence is that the curvature of space-time and the energy associated with the material is shaped. The space-time movement indicates that this can go, and the mass of Matter (which is equivalent to energy) indicates in space-time how it can move.
Chanda week
What I read
Riley Black’s When the earth was green: plants, animals and the greatest romance in evolution are beautiful.
What I look at
I come back Star Trek: Strange new worlds From the start.
What do I work
I think of the newathena X -ray observatory will teach us on the interior of neutron stars.
Chanda Prescod-Weinstein is an associate professor of physics and astronomy at the University of New Hampshire. She is the author of the disorderly cosmos and the next book The Edge of Space-Time: Particles, Poetry and The Cosmic Dream Boogie
Subjects:
- Quantum physics/ /
- space-time
