When Redshift Occurs, What Happens to Light’s Energy? It’s Complex.

Many of us can relate to concerns about inflation. The rising cost of living weighs heavily on our minds, and we often scrutinize what political leaders are doing in response. Yet it’s essential to recognize the terminology issues present in physics, especially since inflation carries a vastly different meaning in this context.

In cosmology, space inflation refers to a model that elucidates why our universe appears so expansive. This theory posits that space-time underwent rapid expansion for a brief duration—around one second—leading to regions of the universe that are now uncommunicative but once were connected.

Understanding such immense scales can be a challenge. How do we truly grasp these vast distances that exceed our everyday experiences? Last month’s column tackled this concept by addressing distance measurement techniques. Yet, this inquiry itself unfolds layers of complexity.

In that discussion, I highlighted how Redshift serves as a crucial tool for gauging distances in space. Imagine a series of balloons being inflated; as they expand, their peaks and troughs elongate. This phenomenon mirrors how light behaves as it travels across the fabric of space-time. The light stretches, increasing its wavelength.

This shift in light wavelengths enables distance calculation. By measuring the wavelength of light from a distant object and comparing it to our observations, we can discern how much space-time has expanded between our position and the observable objects. Such Redshift measurements are consistently corroborated by both astronomical observations and lab experiments.

However, deeper questions linger. From a quantum standpoint, light’s wavelength is tied to its energy content. The stretching of light reduces its energy, resulting in a redshift effect. This phenomenon isn’t merely a nuisance; rather, it presents intriguing insights about quantum mechanics within cosmological discussions.

What’s the dilemma? We prefer consistent principles across physics domains. A core tenet of everyday physics suggests that energy cannot be created or destroyed, only transformed. Thus, if we apply energy conservation to redshifted light, we face the question: where does the lost energy of light go? A curious reader posed this very question.

The response may be surprising. While energy conservation remains a guiding principle, it seems the cosmic realm can, at times, operate differently. Albert Einstein’s theory of general relativity plays a pivotal role here. Though widely recognized for its insights into the fabric of cosmic time and curvature, it also reveals how space-time itself may expand.

A unique aspect of general relativity is that energy conservation isn’t universally applicable. In essence, as light loses energy through redshift, this loss is not considered significant in the grand scheme. Energy doesn’t necessarily have to ‘go’ anywhere; it can merely dissipate.

That’s one way to frame it. Alternatively, we could also address the energy associated with gravitational fields. Historically, conflating these two perspectives has sparked considerable debate. Some argue they represent two facets of the same reality.

Personally, I contend that the essence of energy remains ambiguous. It’s challenging to delineate, yet it’s palpable in connection to physical entities like particles and stars. However, when discussing the energy entwined with space-time curvature, clarity dissolves. Where exactly is this energy located within the continuum of space and time? How concentrated is it at specific junctures? These inquiries reflect the complexities of inflation!

Thus, I find myself aligning with those who suggest that strict energy conservation may not be the most useful concept. What stands clear is the interdependence of space-time curvature and energy related to matter. Space-time’s dynamics guide matter’s trajectory, while matter’s mass (akin to energy) influences how space-time will behave.

Chanda’s Week

What I’m reading

Riley Black When the Earth was Green: The Epic of Plants, Animals, and Evolution beautiful.

What I’m watching

I’m re-watching Star Trek: A Strange New World from the start.

What I’m working on

We are pondering the Newathena X-Ray Observatory to deepen our understanding of neutron star interiors.

Chanda Prescod-Weinstein is an associate professor of physics and astronomy at the University of New Hampshire. She is the author of Cosmos with Disabilities and the forthcoming book, “Edges of Space-Time: Particles, Poetry, and the Universe’s Dreamscape.”