# Questions about relative Space-Time in the Universe

• B
• WesKnight
WesKnight
TL;DR Summary
How do you rectify the ability to alter the present moment, while saying at the same time being from any different point in space observing outward having already occured?
Hello everybody. I have been having a lingering question about the State of the Universe. As humans, we view the Universe's expanse as historical from the vantage point of Earth. For example, 10,000 light years away would have occurred 10,000 years ago. On that same logic, looking at Earth from a point 10,000 light years away, that would have also occured 10,000 years ago. How do you rectify the ability to alter the present moment, while saying at the same time being from any different point in space observing outward having already occured? How do you rectify this, which would otherwise seem counterintuitive?

I'm struggling to understand what you asked. I think it is "how can we affect things in the present if we can only see them in the past". If so, the answer is that we cannot affect things in the present. All causal effects propagate at or below the speed of light, so anything you do now will take time to propagate to whatever you are affecting.

So if you look at the moon you see it as it was about 1.3 seconds ago, and nothing you do now can affect it until at least 1.3 seconds in the future.

Ibix said:
I'm struggling to understand what you asked. I think it is "how can we affect things in the present if we can only see them in the past". If so, the answer is that we cannot affect things in the present. All causal effects propagate at or below the speed of light, so anything you do now will take time to propagate to whatever you are affecting.

So if you look at the moon you see it as it was about 1.3 seconds ago, and nothing you do now can affect it until at least 1.3 seconds in the future.
Thank you. My question is how do we rectify everything happening simultaneously in the Universe, including our ability to make decisions, or have free will, if no matter where you are in the Universe is historical in nature.

If person A were doing something at this present moment on Earth, person B who's at point C in the Universe would observe it X number of light-years in the future, but historically as the past. However, if person A was capable of observing person B at the moment person B observed them, would it then stand to reason then that person A would be capable of seeing that moment in the future? And if so, since everything in the Universe is happening simultaneously, how do you define the agent of free will, as no matter how you view things, the moment HAS happened, even saying the moment WILL happen.

Hopefully this makes sense.

Ibix said:
I'm struggling to understand what you asked. I think it is "how can we affect things in the present if we can only see them in the past". If so, the answer is that we cannot affect things in the present. All causal effects propagate at or below the speed of light, so anything you do now will take time to propagate to whatever you are affecting.

So if you look at the moon you see it as it was about 1.3 seconds ago, and nothing you do now can affect it until at least 1.3 seconds in the future.
With your statement "...the answer is that we cannot affect things in the present" Is the concept of free will already pre-determined?

WesKnight said:
However, if person A was capable of observing person B at the moment person B observed them, would it then stand to reason then that person A would be capable of seeing that moment in the future?
You cannot see what's happening "now" elsewhere in the universe, so asking what would happen if we could is asking what the laws of physics say about what would happen in a situation they describe as impossible - if it does happen then we know our understanding of physics is wrong and we would be wrong to use the laws we know to try to predict anything. It's like asking "if this sheep is all black and all white, what colour is it?" The answer is that a sheep that is both 100% black and 100% white is impossible as far as we know. So we can't predict what one would look like if it did turn out to exist.
WesKnight said:
since everything in the Universe is happening simultaneously
It isn't at all clear that this is the case. In fact, relativity doesn't have a natural concept of "simultaneously" - you have to impose a definition if you want one, and multiple different definitions are possible. Not realising that is probably the single biggest stumbling block to understanding relativity.
WesKnight said:
free will
I think you'd have to define carefully what you mean by "free will" before that's even answerable.

Generally, physics is a bad place to look to if you want to think about free will. We can't rewind time to find out if you'd ever behave differently in the same circumstances, so "I have free will" is not a testable proposition.

WesKnight said:
With your statement "...the answer is that we cannot affect things in the present" Is the concept of free will already pre-determined?
Please take care not to swerve too much in the direction of philosophy here. We don't allow philosophical discussions at PF. Thank you.

WesKnight said:
With your statement "...the answer is that we cannot affect things in the present" Is the concept of free will already pre-determined?
Your question makes no sense to me at all. What has light traveling about the universe got to do with "free will".

berkeman said:
Please take care not to swerve too much in the direction of philosophy here. We don't allow philosophical discussions at PF. Thank you.
My apologies. I agree it is philosphical. I'll re-phrase and use how altering space-time is possible. Above, Ibix already answered my question about the past, present, and future operating simulaneously. I was attempting to understand how to reconcile it, if laws demonstrated the Universe operated that way. From what I understood above, the past propagates, and our choices further propagates, which triggers cause and effect for the moment in time we're in at that time (i.e., future).

PeroK said:
Your question makes no sense to me at all. What has light traveling about the universe got to do with "free will".
Hello PeroK. The question was under the presumption that the Universe was in sync, functioning simultaneously. That would have to reconcile how the past, present, and future function in space-time, if altered (including by humans) to maintain synchronization. I was posing that if the Universe was in sync in that manner, a person at point X in the Universe would observe an event which happened at point Y, which then may mean the if the person at point X observed the alteration in space-time, the person at point Y which caused the event could also observe the person at point X who observed it, therefore observing the future. Furthermore, how we are capable of altering it if space-time was syncronized in that manner. Again, if it doesn't make sense, that was just trying to understand any correlation in space-time.

WesKnight said:
Hello PeroK. The question was under the presumption that the Universe was in sync, functioning simultaneously.
The universe is not "in sync" in this sense.

In the classical model (i.e. ignoring the non-local aspects of quantum mechanics), the evolution of the universe here depends only on its state in our past light-cone. Similarly, the influence of decisions made here only affects the universe within our future light-cone.

The portion of the universe that we might label as "simultaneous" with us here and now is part of neither our past light-cone nor our future light-cone. It is "elsewhere". Its evolution is independent of anything we do here and now. Similarly, our current evolution is independent of anything taking place "elsewhere".

That is, "here" evolves independently from "there".

This is the standard interpretation.

There is also the block universe interpretation in which the universe exists as a completed four dimensional whole and any supposed "free will" is an illusion arising from an inability to model ourselves with perfect fidelity.

Klystron, russ_watters and WesKnight
jbriggs444 said:
The universe is not "in sync" in this sense.

In the classical model (i.e. ignoring the non-local aspects of quantum mechanics), the evolution of the universe here depends only on its state in our past light-cone. Similarly, the influence of decisions made here only affects the universe within our future light-cone.

The portion of the universe that we might label as "simultaneous" with us here and now is part of neither our past light-cone nor our future light-cone. It is "elsewhere". Its evolution is independent of anything we do here and now. Similarly, our current evolution is independent of anything taking place "elsewhere".

That is, "here" evolves independently from "there".

This is the standard interpretation.

There is also the block universe interpretation in which the universe exists as a completed four dimensional whole and any supposed "free will" is an illusion arising from an inability to model ourselves with perfect fidelity.
Thank you for that wonderful response!

WesKnight said:
With your statement "...the answer is that we cannot affect things in the present" Is the concept of free will already pre-determined?
No, there are no implications here for free will. All the travel time delay means is that you have to wait to find out what happens elsewhere. There are no profound implications of that for our reality here.

Klystron and PeroK
Think about the simpler case - hearing sounds on earth. After you hear something - a car horn, for example - it happened in the past. It just took sound a period of time to reach your ears.

Does this bother you? If not, what is the difference, except in the numerical answer - between this situation and the one you propose?

FactChecker
If you pick up your mail a week later, that doesn't mean anything profound about your ability to change current reality. What we, or anyone, see a thousand years later does not mean anything profound.

russ_watters
This discussion reminds me of a thought experiment I posted on a different board awhile back - where you (for arguments sake) have a super-duper zoom camera positioned 6 light seconds out from earth, aimed at your house, and is equipped with a 10 petapixel sensor and a quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.

You are walking across your back yard and see the remote sitting on a bench in your yard, so on a whim you walk over and trigger the remote, the whole exercise takes about 3 seconds, from the time you thought of it to the time you trigger the shutter.

When the picture arrives on your phone 6 seconds later, you get an image of yourself walking across your back yard, before you even thought about taking the image..

berkeman
Glenstr said:
This discussion reminds me of a thought experiment I posted on a different board awhile back - where you (for arguments sake) have a super-duper zoom camera positioned 6 light seconds out from earth, aimed at your house, and is equipped with a 10 petapixel sensor and a quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.

You are walking across your back yard and see the remote sitting on a bench in your yard, so on a whim you walk over and trigger the remote, the whole exercise takes about 3 seconds, from the time you thought of it to the time you trigger the shutter.

When the picture arrives on your phone 6 seconds later, you get an image of yourself walking across your back yard, before you even thought about taking the image..
What does this thought experiment have to do with physics?

Glenstr said:
is equipped with a 10 petapixel sensor and a quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.
How exactly does this FTL communication work?

Glenstr said:
quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.
This is not possible because entanglement doesn't work the way you're thinking. Although you can trigger the remote in your back yard and (in some interpretations) this will collapse the wave function, nothing we can do at the camera end can determine that the wave function has collapsed. For more information on this you can take a look at some of the many threads in our Quantum Mechanics subforum explaining why entanglement cannot be used for instantaneous or faster-than-light communication.

FactChecker
berkeman said:
How exactly does this FTL communication work?
It doesn't - it's impossible - like a petapixel camera with resolution that good..

It's just a fun thought experiment, nothing more.

Glenstr said:
It's just a fun thought experiment, nothing more.

Thought experiments have to have basis in physics.

Glenstr said:
It doesn't - it's impossible - like a petapixel camera with resolution that good..

It's just a fun thought experiment, nothing more.
So that's 5 minutes of my life that I'll never get back. Noted...

Glenstr said:
quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.
This is the particular piece of SF (I'd use another two letter acronym involving S, but am aware I'm drunk) that renders the whole thing nonsense. "Instantly, no matter the distance" involves assumptions about what "instantly" means that aren't really supportable (in general) in a relativistic universe.

You all clearly missed the (for arguments sake) sake part in my comment and it seems to be causing undue stress among some, so I'll delete the post..

Glenstr said:
You all clearly missed the (for arguments sake) sake part in my comment
Not quite. The problem is "for arguments' sake" still requires logical coherence. The bit of your post I highlighted destroys that, and we're left with a "so what if black were white...?" kind of question.

That may not be apparent to you, but that's why I highlighted the specific problem with your post - so you can learn where you went wrong if you want.

Glenstr said:
You all clearly missed the (for arguments sake) sake part in my comment and it seems to be causing undue stress among some, so I'll delete the post..

Glenstr said:
This discussion reminds me of a thought experiment I posted on a different board awhile back - where you (for arguments sake) have a super-duper zoom camera positioned 6 light seconds out from earth, aimed at your house, and is equipped with a 10 petapixel sensor and a quantum entangled remote that triggers the shutter instantly, no matter the distance from the camera.

You are walking across your back yard and see the remote sitting on a bench in your yard, so on a whim you walk over and trigger the remote, the whole exercise takes about 3 seconds, from the time you thought of it to the time you trigger the shutter.

When the picture arrives on your phone 6 seconds later, you get an image of yourself walking across your back yard, before you even thought about taking the image..

## What is the theory of relativity?

The theory of relativity, developed by Albert Einstein, consists of two main parts: special relativity and general relativity. Special relativity, introduced in 1905, deals with objects moving at constant speeds, particularly those close to the speed of light. It introduces the concepts of time dilation and length contraction. General relativity, introduced in 1915, extends these ideas to include gravity, describing it as the curvature of space-time caused by mass and energy.

## How does time dilation work?

Time dilation is a phenomenon predicted by the theory of relativity, where time passes at different rates for observers in different frames of reference. In special relativity, an observer moving at a high velocity relative to another will experience time more slowly. In general relativity, a stronger gravitational field (closer to a massive object) causes time to pass more slowly compared to a weaker gravitational field.

## What is the space-time continuum?

The space-time continuum is a four-dimensional framework that combines the three spatial dimensions (length, width, height) with time into a single interwoven continuum. In this model, events are described in terms of their position in both space and time. This concept is fundamental to the theory of relativity, where the geometry of space-time is affected by the presence of mass and energy.

## How does gravity affect space-time?

According to general relativity, gravity is not a force between masses but rather a curvature of space-time caused by the presence of mass and energy. Massive objects like stars and planets create dents or curves in the fabric of space-time, and these curves dictate the motion of objects, causing them to follow paths called geodesics. This curvature is what we perceive as gravity.

## What are black holes and how do they relate to space-time?

Black holes are regions of space-time where the gravitational pull is so strong that nothing, not even light, can escape from them. They are formed when massive stars collapse under their own gravity at the end of their life cycles. In terms of space-time, black holes create extreme curvature, essentially creating a "hole" in the fabric of space-time. The boundary around a black hole is called the event horizon, beyond which events cannot affect an outside observer.

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