Moving at Light Speed: Relativistic Effects Explained

Click For Summary

Discussion Overview

The discussion centers on the relativistic effects of moving at or near the speed of light, particularly exploring hypothetical scenarios and the implications of such speeds on time perception and physical phenomena. It includes considerations of what it means to travel at light speed, the behavior of photons, and the nature of time in relation to massless particles.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that if one could travel at the speed of light, they would experience no passage of time, leading to questions about the nature of actions and destinations from that perspective.
  • Others argue that only massless particles can travel at light speed, implying that humans cannot actually reach that speed.
  • A participant suggests considering travel at nearly the speed of light, noting that significant time dilation could allow for vast distances to be covered within a human lifetime.
  • There is a discussion about whether photons experience time when traveling through different media, with some asserting they do not experience time at all, while others suggest that the concept of time may differ in various contexts.
  • Some participants mention polaritons, suggesting that they have a finite lifetime and may experience time differently than photons, leading to further exploration of the implications of this distinction.
  • There are conflicting views on whether the finite lifetime of photons or polaritons indicates any experience of time, with some emphasizing that massless particles cannot decay and thus do not experience time.
  • Participants express uncertainty about the implications of light traveling through media and whether it affects the experience of time for photons.

Areas of Agreement / Disagreement

Participants do not reach consensus on several key points, particularly regarding the experience of time by photons and the implications of their behavior in different media. Multiple competing views remain on the nature of time and the behavior of massless particles.

Contextual Notes

Discussions include unresolved assumptions about the definitions of time and experience, as well as the implications of relativistic effects that are not fully explored. The complexity of the interactions between light and matter, particularly in the context of polaritons, adds layers of uncertainty to the discussion.

  • #31
JarodB said:
The big bang was the "explosion" from a very very small ball of infinitly dense matter, before the explosion was just the ball of matter / energy.

I think you might have the right sort of idea, but there are some serious misstatements.

A very very small ball of infinitely dense matter is indistinguishable from a very big ball of infinitely dense matter. It has infinite mass. If the age of the universe is not infinite, then the volume of the universe is not infinite and if you put an infinite mass in a finite universe the matter is still going to be infinitely dense.

As Dave said, it wasn't matter originally anyway. Nor was the big bang an explosion. Perhaps it is worth remembering that "big bang" was initially a pejorative. It wasn't meant to describe what is now the standard cosmological model, it was meant to ridicule it.

Plus, you say "before the explosion was just the ball of matter / energy" which implies (even if not intentionally) that the "ball" was surrrounded by empty space on top of suggesting that there was a sensible "before". At t=0 (where t is now about 14 billion years), there was nothing. At t=tpl, a Planck time, there was the entire energy of the universe as tightly compacted as it can be.

Here's where I have to bow to quantum physicists, I suspect that the maximum amount of energy you can fit into one Planck cube (or a Planck volume) is the energy associated with the Planck mass (it is also the energy associated with a photon with a frequency of 1/tpl). (The wikipedia article on http://en.wikipedia.org/wiki/Planck_energy" says this is "probable".)

So, if I am right, one Planck time after t=0, all the energy of the universe would be in a quite small space (with a radius of about 10-15). After the second Planck time, it would be a radius of about 10cm (very roughly). This would require the space to have expanded at greater than the speed of light with a very high Hubble constant, but that would be consistent with a Hubble constant which corresponds with the age of the universe (as it does today) and the fact that the edges of the universe would be outside of the Hubble distance for that value of the Hubble constant. (The Hubble distance is the distance away that something has to be to be moving at the speed of light. That makes it the radius of the observable universe.) I also think that other factors would come into play, like gravity (because concentrations of energy resist the expansion of the universe, as do galaxies today) and heat, although this may not figure until you get condensation of matter.

After that, I think you would have something akin to an explosion (to the same extent that quickly blowing up a balloon without it bursting is an explosion), or at least the beginnings of lumpiness in the universe.

Anyway, at Planck time, the energy of the universe was not associated with one photon with a very high frequency (just not possible), nor was it infinitely dense. If the Hubble constant is linked to the age of the universe, then it doesn't make sense to have any before the big bang. (Although, to be as comprehensive as I can, it is not impossible that the Hubble constant represents the age of the universe since the big bang. That just means that the time before the big bang is meaningless, in a similar way that time in an empty static universe would be meaningless.)

cheers,

neopolitan
 
Last edited by a moderator:
Physics news on Phys.org
  • #32
When did time start
 
  • #33
At the big bang.So the big bang was t = 0
 
  • #34
neopolitan said:
So, if I am right, one Planck time after t=0, all the energy of the universe would be in a quite small space (with a radius of about 10-15). After the second Planck time, it would be a radius of about 10cm (very roughly).

It always puzzled me, how 10^34 plank distances can be created during 1 plank time...
 
  • #35
Dmitry67 said:
It always puzzled me, how 10^34 plank distances can be created during 1 plank time...

Well planks length is the distance light can travle in planks time (t_{p}\ =\ 5.3906(40)\ \times\ 10^{-44}\ s), we know the universe is slowing down exponentially but we don't know if it will stop and collaps on its self.
 

Similar threads

Undergrad One way speed of light
  • · Replies 26 ·
Replies
26
Views
612
High School Let me ask a thing about the Speed of Light
  • · Replies 6 ·
Replies
6
Views
2K
High School Problem about postulate of the invariance of the speed of light
  • · Replies 33 ·
2
Replies
33
Views
4K
High School Thought Experiment: Behavior of shadow of object moving at speed c
  • · Replies 14 ·
Replies
14
Views
2K
High School Why Does the Speed of Light Max Out at 186,282 Miles Per Second?
  • · Replies 120 ·
5
Replies
120
Views
9K
Undergrad Is the concept of a one-way speed of light meaningful and measurable?
  • · Replies 25 ·
Replies
25
Views
5K
High School Why is it impossible to go faster than the speed of light?
  • · Replies 21 ·
Replies
21
Views
5K
High School Constant Speed of Light: Low Speed Explained
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Proving speed of light constant “c” is the same in all directions?
  • · Replies 11 ·
Replies
11
Views
2K
Graduate 1-Way Speed of Light
  • · Replies 42 ·
2
Replies
42
Views
3K