Is the Future Fixed?

Have you ever wondered a possibility where a person’s actions do not shape their future, but are already predefined in the four-dimensional spacetime – meaning that all the past, present and future events are fixed and were always meant to happen? Or is it simply one’s present actions that define its future?

Now versus Simultaneity

To break this question down, I will define certain elements that make up our perception of the term “present”. Imagine the following: It is October 1604, and you happen to be next to Johannes Kepler when both of you notice a star that seems new in the sky. You observe the star for sometime and notice it expand, later on defining it as a Supernovae, SN 1604 (Uri). When a friend asks you what happened, you answer saying: “We observed a Supernovae now“. However, SN 1604 is 20,000 light years away, so the event that is being observed has occurred 20,000 years ago and hence is not occurring simultaneously to your observations. This example highlights the difference between current observations and simultaneity occurrence. This can be shown on a Minkowski (space over time) diagram.

The light travels at 45 degrees on a Minkowski diagram by definition.

Simultaneity can be illustrated as a surface. Picture yourself standing between two flashlights at some distance. If they are turned on simultaneously, the light beams will travel and reach you at the same time. This allows us to define a surface of simultaneity – surface on which the events happen simultaneously relative to you.

However, what if you are running? If you are moving and so are the flashlights, the light beams will reach you at the same time only if one of the flashlights is turned on earlier, since light travels at 45 degrees regardless of the motion. And even though the flashlights were not turned on simultaneously, they did reach you at the same time, allowing us to define the new surface of simultaneity. 

This means that for two people, one moving and one stationary, their simultaneity surfaces do not agree with each other (Sabine Hossenfelder).

Okay. So what? 

Well, this is where it gets interesting. Picture Andromeda galaxy being filled with Andromedians, its living creatures, which decide the attack us. First they will discuss their plans and then they will take off on their spaceship. Let’s imagine you are standing looking up into the sky, while simultaneously the Andromedians are discussing their plans of invasion. Johannes Kepler, your friend, happens to run by you looking into the sky. Both of you will observe the same event that happened 2.5 million years ago (Troche). However, will there be the same event occurring in Andromeda galaxy simultaneously for both of you?

By our definition of simultaneous surfaces, his simultaneous event will be different, an event that happens much further in time. While for you it will be the the discussion of Andromedians’ plans, for Mr. Kepler it could very much be the Andromedian take off.

Let’s illustrate this using a Minkowski diagram once again, to show why that is.

The diagram shows that simultaneity surfaces are different, meaning that while for you your now is occurring 2.5 million light years away (the distance to Andromeda), for Johannes your future is what is currently occurring. 

This raises an issue – if the future has already happened for Johannes, is the future fixed for you? And if it is fixed, can we shape it in the first place, or are we moving along the timeline that has been predefined for us?

This is what is called Block Universe (Andersen). A theory that proposes that all moments – past, present and future all exist simultaneously. Looking at our Minkowski diagram, we can be postulate that the time difference between simultaneously occurring events for you and Joannes will depend on the distance of the simultaneous events as well as the speed at which Joannes is moving with.

I will leave it up to you to decide whether the future is fixed, just remember – your answer might already exist. And for an Andromedian far far away, you have already this blog…

References:

Andersen, Tim. “Roger Penrose’s Paradox Won’t Tell Us If the Past and Future Exist.” Medium, The Infinite Universe, 29 Apr. 2025, medium.com/the-infinite-universe/roger-penroses-paradox-won-t-tell-us-if-the-past-and-future-exist-f5a6bf00f731. Accessed 7 May 2025.

Brasch, Klaus R. “Get to Know the Andromeda Galaxy.” Astronomy Magazine, 1 Sept. 2024, www.astronomy.com/science/getting-to-know-the-andromeda-galaxy/.

Sabine Hossenfelder. “The Andromeda Paradox Even Confuses Physicists.” YouTube, 27 Apr. 2025, www.youtube.com/watch?v=i7Rx6ePSFdk. Accessed 7 May 2025.

Siegel, Ethan. “When Einstein Met H.G. Wells.” Starts with a Bang!, 14 Jan. 2015, medium.com/starts-with-a-bang/when-einstein-met-h-g-wells-425372d21821.

Troche, Kat. “October’s Night Sky Notes: Catch Andromeda Rising! – NASA Science.” Nasa.gov, 1 Oct. 2024, science.nasa.gov/solar-system/skywatching/night-sky-network/catch-andromeda-rising/.

Uri, John. “420 Years Ago: Astronomer Johannes Kepler Observes a Supernova – NASA.” NASA, 9 Oct. 2024, www.nasa.gov/history/420-years-ago-astronomer-johannes-kepler-observes-a-supernova/.