What Does It Mean to Travel at the Speed of Light in the 4th Dimension?

Click For Summary

Discussion Overview

The discussion explores the concept of traveling at the speed of light in the fourth dimension, particularly in the context of general relativity, where the fourth dimension is often considered to be time. Participants examine the implications of this idea, including the nature of space-time and the experiences of observers moving at relativistic speeds.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that one cannot travel at the speed of light unless one is a photon, which raises questions about self-awareness and the nature of experience at such speeds.
  • Others propose that traveling in the fourth dimension involves a transformation of time into space and vice versa, suggesting that different observers perceive these dimensions differently based on their relative velocities.
  • A participant mentions that as one approaches the speed of light, time appears to slow down for outside observers, while the traveler perceives time normally, indicating a lack of absolute reality.
  • There is a discussion about Hermann Weyl's concept of a four-dimensional universe populated by four-dimensional objects, where observers' consciousness moves at the speed of light, though this idea is noted as speculative and not widely accepted among physicists.
  • Some participants challenge the relevance of self-awareness in the context of physics, arguing that it does not pertain to the physical principles being discussed.
  • One participant attempts to bridge the concept of time as a dimension with the experience of consciousness, suggesting that time "feels" different depending on one's state of awareness.

Areas of Agreement / Disagreement

Participants express multiple competing views on the nature of time and space, the implications of traveling at the speed of light, and the relevance of self-awareness in these discussions. The conversation remains unresolved, with no consensus reached on several key points.

Contextual Notes

Limitations include the speculative nature of some concepts presented, such as Weyl's model, and the varying interpretations of the relationship between time and space. The discussion also highlights the challenge of conceptualizing relativistic effects and their implications for observers.

Zac Einstein
Messages
26
Reaction score
0
How is it like to travel at the speed of light in the 4th dimension?
and according to general relativity, the 4th dimension is time, what does that mean ?...and why? :rolleyes:
 
Physics news on Phys.org
You cannot travel at the speed of light unless you are a photon in which case you would not be self-aware, so there is no answer to that part of your question.

As to traveling in 4D space-time, you are doing in time right now, 1 second per second. Your "speed" depends on what reference point you chooose.
 
Thinking about time as a fourth dimension means that it morphs into space and space into it. Different observers may see them differently.

So space and time vary with velocity which is not expected in Newtonian physics. It turns out that space and time are not fixed and immutable, but the speed of light IS fixed, also unlike Newtonian physics where forces act instantaneously. The formula for the addition of two velocities is only approximately v1 plus v2 that we typically learn is early school. You can read about that here:

http://en.wikipedia.org/wiki/Addition_of_Velocities_Formula


As you approach the speed of light, your time as observed by an outside inertial observer appears to run slower than theirs...you see it locally as passing normally. You observe space in front contracted, so the distance you need to travel is foreshortened, but an outside inertial observer is unaware of your observation change from theirs. Different observers in different frames of reference see different things...there is no 'absolute' reality.

There is no intuitive reason for all this: if it were 'obvious' it would not have taken an Einstein to realize what's happending. But once it was understood the speed of light is very fast, but finite, a number of pieces fall into place. So with relativity, and separately quantum mechanics, we need some new ways of thinking, some new mathematics and a new perspective because what we observe macroscopically and at slow speed is not how nature behaves at high speed or microscopically. Our senses are just not attuned to those phenomena.
 
Naty1 said:
Thinking about time as a fourth dimension means that it morphs into space and space into it. Different observers may see them differently.
This is obviously very difficult to picture. One analogy that may help the imagination perhaps is that of the quote by Yeats: "How can we separate the dance from the dance?"

If we conceive of time as a measure of relative movement (ie, the pacing of any given movement with respect to a standard movement generated by an apparatus we call a clock) then spacetime as a 4-dimensional theatre takes that question one step further to "How can we separate the dancer and the dance from the space they occupy?". The physical answer is that we simply can't, neither the dancer (matter) nor the dance (relative movement, which implies time) can exist independently of the space they occupy or 'consume' so to speak.

IH
 
Last edited:
This is obviously very difficult to picture...

It's an utterly CRAZY idea...but it works! So far, we have no better description.
 
phinds said:
You cannot travel at the speed of light unless you are a photon in which case you would not be self-aware, so there is no answer to that part of your question.
Electrons and protons and neutrons are not self-aware either. And guess what we are made of a very large collection of them.

What has this whole self-aware thing to do with physics?
 
Zac Einstein said:
How is it like to travel at the speed of light in the 4th dimension?
and according to general relativity, the 4th dimension is time, what does that mean ?...and why? :rolleyes:

If x^4 = ct then dx^4 / dt = c, which is the speed of light signals. This is not a velocity.

According to general relativity the 4th dimension does not need to to be time.
 
Passionflower said:
Electrons and protons and neutrons are not self-aware either. And guess what we are made of a very large collection of them.

What has this whole self-aware thing to do with physics?

I think it's because the OP said "How is it like?" suggesting that he wants to know what it would feel like...
 
Zac Einstein said:
How is it like to travel at the speed of light in the 4th dimension?
and according to general relativity, the 4th dimension is time, what does that mean ?...and why? :rolleyes:

In Hermann Weyl's concept the universe is 4-dimensional populated by 4-dimensional objects, including the physical bodies of the observers. So, with this model there is no motion at all of the physical bodies (not even motion along the 4th dimension).

But, every observer's consciousness moves along his respective 4th dimension at the speed of light, c. However, there doesn't seem to be a consensus among physicists about this concept, and on this forum such a concept is considered speculation and therefore not an appropriate topic.
 
  • #10
Naty1 said:
Different observers in different frames of reference see different things...there is no 'absolute' reality.

Unless the universe is 4-dimensional. But, this is not an appropriate topic for this forum.
 
  • #11
Passionflower said:
Electrons and protons and neutrons are not self-aware either. And guess what we are made of a very large collection of them.

What has this whole self-aware thing to do with physics?

Perhaps a poor choice of words, but it is perfectly valid thought experiment to ask what an electron or proton would "experience" moving at .5c. The fact that they have no awareness does not mean we cannot meaningfully ask and answer what happens to them.Contrarily, we cannot do this with photons. Photons, since they travel at c, do not have a valid reference frame at all. It is nonsensical to ask what a photon experiences.
 
  • #12
Passionflower said:
Electrons and protons and neutrons are not self-aware either. And guess what we are made of a very large collection of them.

What has this whole self-aware thing to do with physics?

The the sequence of space-time diagrams in the sketch below depicts the situation for an observer moving at ever greater relativistic speeds. You can see that if a photon was "self aware", his total world line would be experienced simultaneously, evidently becoming unintelligible. His X1 and X4 axes have become colinear. Thus, his X1 component of his instaneous 3-D cross-section view of the 4-D universe is colinear with the 4th dimension. Of course this kind of discussion is not appropriate for this forum.
Approach_LightSpeed_C.jpg
 
Last edited:
  • #13
Zac Einstein said:
How is it like to travel at the speed of light in the 4th dimension?
and according to general relativity, the 4th dimension is time, what does that mean ?...and why? :rolleyes:

It means it is one of the measurements people take when making certain observations of spacetime.

Length and time, simple as that. There is of course a unique relationship between these two measurements which is apparent in the interval equation..thing. :)

Trying to bridge that to an answer of what it "feels" like;
The above is true from any inertial perspective, from great big to nearly the smallest. Even a rock "ages" in the sense that its composition changes at regular Intervals.

This is important, the regular intervals in the changing of the rocks composition (radiocarbon dating) are assumed to be purely timelike, that is the time measurement is assumed to be a measurement of just time and not distance, as would be the case if the rock traveled at relativistic speeds compared to the archeologist that dates the rock)

By whatever blessing this changing of composition along a purely timelike interval can amount to a point of self awareness. Where there is consciousness "along" that purely timelike interval, the 4th dimension time.

So time "feels" like when you're not unconscious :smile:, which is far from being measurable as an observation with rulers & clocks and is a different field of study all together.

lol Naty1 "our" best description of time as a dimension is not "Thinking about time as a fourth dimension means that it morphs into space and space into it." In fact I think that's one of the difficulties in understanding time as a dimension; it's relationship with length. Unless "morphs" has some loaded definition I don't know of.
 
Last edited:
  • #14
bobc2 said:
The the sequence of space-time diagrams in the sketch below depicts the situation for an observer moving at ever greater relativistic speeds. You can see that if a photon was "self aware", his total world line would be experienced simultaneously, evidently becoming unintelligible.
And again what on Earth has self-awareness to do with it?
 
  • #15
Passionflower said:
And again what on Earth has self-awareness to do with it?

What is "it" that self awareness has nothing to do with?
 
  • #16
nitsuj said:
What is "it" that self awareness has nothing to do with?
The world line.
 
  • #17
Passionflower said:
And again what on Earth has self-awareness to do with it?

This question was answered in post 11.

Read it. Embrace it. Move on.
 

Similar threads

High School What Is the Fourth Dimension and How Does It Work?
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad How can the Universe know when you change directions?
  • · Replies 42 ·
2
Replies
42
Views
4K
Undergrad Spacetime expansion - time dimension expansion
  • · Replies 48 ·
2
Replies
48
Views
4K
Graduate Small and large extra dimension(s) of the physical space
  • · Replies 12 ·
Replies
12
Views
2K
High School Moving in the 4th Dimension -- Does Time have a velocity?
  • · Replies 20 ·
Replies
20
Views
4K
High School Is time an illusion?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Block Universe Theory: Implications & Multiverse
  • · Replies 6 ·
Replies
6
Views
3K
High School 4th spatial dimension thought experiment
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad How Can You Approach Steve Without Being Doppler-Shifted?
  • · Replies 4 ·
Replies
4
Views
1K
Graduate Could the curvature of space in general relativity represent a 4th dimension?
  • · Replies 13 ·
Replies
13
Views
3K