Part 2: Exploring the Interplay Between Cosmic Time Dilation and High-Speed Travel

Does One Cancel Out the Other?

In Part 1, we discussed a November 2024 paper, “Supernovae Evidence for Foundational Change to Cosmological Models” (ARXIV), which suggests that cosmic voids—those vast stretches of mostly empty space between galaxies—may experience time more quickly than regions of higher matter density. This idea challenges the conventional interpretation of the universe’s accelerating expansion as being caused by dark energy. Instead, it points to time dilation effects in these sparsely populated regions of the cosmos.

We also explored the ways this new perspective might reshape our trust in the longstanding Λ Cold Dark Matter (ΛCDM) model, and how it aligns with timescape cosmology — an approach that proposes our observations of “acceleration” might be influenced by where and how time flows differently across cosmic scales.

One question that arose from our initial discussion is particularly intriguing: If time is speeding up in cosmic voids, but objects traveling close to the speed of light experience time slowing down (per special relativity), do these effects cancel each other out in any meaningful way? In this Part 2 article, we’ll dig into the details behind that question and see why these two phenomena aren’t exactly opposite sides of the same coin.

Recap: Two Different Types of “Time Dilation”

1. Cosmic Time Differences (Inhomogeneous Cosmology)

In the context of timescape cosmology, the flow of time in vast, low-density voids might be different compared to galaxy-rich regions. On cosmological scales, matter isn’t distributed evenly, so large expanses of emptiness could have measurably different gravitational fields. If gravity affects the passage of time — even subtly — then clocks in voids could tick at a faster rate relative to clocks in denser areas. This is essentially a general relativistic effect, woven into how the universe evolves on a grand scale.

2. Special Relativity (High-Speed Travel)

When an object moves at speeds approaching the speed of light, special relativity comes into play:

• From the traveler’s perspective: Their own clock feels normal.
• From an outside observer’s perspective: The traveler’s clock appears to slow down significantly.

This time dilation is a direct consequence of traveling at high velocity. It’s essentially a local effect that becomes noticeable anytime you measure events from the perspective of a relatively stationary observer watching someone zip by at high speed.

Why They Don’t Simply “Cancel”

Local vs. Global Perspectives

Inhomogeneous cosmology deals with how different parts of the universe measure time. The concept that voids might experience a quicker flow of time than matter-dense regions refers to a global phenomenon across the cosmos. Meanwhile, relativistic time dilation (i.e., slowing of time for someone traveling near light speed) depends on the relative velocity between an observer and a fast-moving object — very much a local phenomenon.

Because they affect time measurements on different scales and from different points of view, they aren’t mirror images that negate each other. Think of one as a large-scale shift in the “baseline” ticking rate, and the other as a near-light-speed shift that shows up between two specific frames of reference.

Magnitude of Effects

The difference in how time might flow between cosmic voids and dense clusters could be subtle — fractions of a percent, perhaps noticeable only by very precise astronomical measurements across billions of years. In contrast, if you’re traveling at, say, 99.9% the speed of light, the time dilation you experience from a stationary observer’s perspective can be extreme. One effect might be minuscule in day-to-day terms, while the other can be huge, even over short durations.

Clocks for Different Observers

If you were in a spaceship moving near light speed and you traveled through a cosmic void, you’d still be subject to the usual rules of special relativity. Even if the void has its own “faster” local sense of time, your personal clock and your biological processes won’t suddenly cancel out that near-light-speed slowdown.

An outside observer — perhaps in a dense galactic region — would see two things:

1. Your time running slow because you’re traveling close to the speed of light.
2. A baseline difference in the flow of time between the cosmic void and their own region.

These combined effects would appear in that observer’s measurements, but they don’t automatically negate one another.

A Closer Analogy

Imagine comparing two houses that set their thermostats differently. One house is very cold, while the other is kept quite warm. Now, if you put on a thick winter coat (like traveling near light speed) in the warm house, you’ll still feel hot — your coat doesn’t cancel out the warmth of that environment in a neat, one-to-one way. The house’s ambient temperature and your coat both affect how you perceive heat, but they operate on different layers. Similarly, cosmic time differences and special relativistic time dilation are both at play, but they’re separate influences.

Future Questions

As research continues, especially with more detailed measurements from next-generation telescopes, we’ll gain better insights into just how pronounced the time-flow differences are in cosmic voids. If the time disparities turn out to be significant, they could lead to new ways of interpreting supernova data, galaxy redshifts, and even gravitational wave signals. On the other hand, if they remain minimal, it might simply fine-tune our understanding rather than overhaul it.

For those intrigued by this blending of cosmological theory and relativity, it’s a reminder that the universe rarely dishes out simple yes-or-no answers. We’re looking at a tapestry of effects woven through the fabric of space and time, and exploring how they interlock is at the very heart of modern cosmology.