Experience Travel on a Photon: Hitch-Hiker's Guide to the Universe

In summary, the conversation discusses the concept of time dilation and its implications for a hypothetical hitch-hiker traveling at the speed of light. It also raises a subsidiary question about the existence of a frontier between space and no-space in a finite universe. The possibility of a beam of light traveling at the speed of light as experienced by the hitch-hiker is also mentioned, but it is noted that this is not possible due to the nature of light and the laws of physics. The conversation ends with a recommendation to change the focus from a photon to a beam of light for a more direct discussion.
  • #1
Karl24
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TL;DR Summary
What's the experience of travel like for a photon?
We know that as speed increases, time slows, and at the speed of light time apparently ceases. Imagine a hypothetical hitch-hiker sitting on a photon and speeding through the universe at -- well, the speed of light. If time has stopped for him (her?), what is his experience of his journey? Are all locations and all times along his path of travel an instantaneous 'everywhere' and 'everywhen' for him?

And a subsidiary question: since the universe is finite, presumably there is eventually a frontier between space and no-space. Depending on where his photon was emitted, it could be that the hitch-hiker will never reach that frontier, because the accumulating expansion of space itself may exceed his rate of travel. But assuming the journey began somewhere already near the edge of space and the frontier was reachable, what happens when he reaches it? Does his mere presence extend the universe, and he continues merrily on his way? Or does he bounce back? Or cease to exist? Just wondering, before I book my ride!
 
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  • #2
Karl24 said:
We know that as speed increases, time slows, and at the speed of light time apparently ceases
You’ll often hear time dilation described that way, but it’s not right. One way of seeing the problem is to consider that right now you (along with the Earth and the entire solar system) are moving very close to speed of light relative to some cosmic ray particle zipping through - but is time slowed for you?
Imagine a hypothetical hitch-hiker sitting on a photon and speeding through the universe at -- well, the speed of light. If time has stopped for him (her?), what is his experience of his journey? Are all locations and all times along his path of travel an instantaneous 'everywhere' and 'everywhen' for him?
It’s not possible to draw any conclusions from this hypothetical, for about the same reason that any thought process that starts “Imagine an integer that multiplied by one is not equal to itself….” must lead to bogus conclusions - the premise is inconsistent. The problem here is that the light moves at speed ##c## relative to everything so we’re trying to imagine a situation in which our flash of light is both at rest relative to the hitchhiker and moving at speed ##c## relative to the hitchhiker - internally contradictory from the start. (This question comes up often enough that we have a FAQ: https://www.physicsforums.com/threads/rest-frame-of-a-photon.511170/).

And a subsidiary question: since the universe is finite,
Is it? That’s still an open question. But even if the universe is finite it does not follow that
presumably there is eventually a frontier between space and no-space.
Consider the two dimensional surface of the spherical earth. It’s finite, but there is no edge, no frontier between surface and non-surface. No matter how far you walk in any direction, there’s always room in front of you for your next step.

If the universe is finite it will be curved in such a way that it has no edge.
 
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  • #3
Nugatory said:
If the universe is finite it will be curved in such a way that it has no edge.
This is a physically reasonable assumption but I don't believe you can state it with certainty. The formalism does not exclude finite spacetimes which are manifolds with boundaries, no?
 
  • #4
Karl24 said:
Summary:: What's the experience of travel like for a photon?
There is no way to answer this. By the way, I recommend that the question be changed so that you refer to a beam of light instead of a photon. Even then the question can't be answered, but a discussion of why will be more direct because you won't have to enter into the realm of quantum physics.
Karl24 said:
We know that as speed increases, time slows, and at the speed of light time apparently ceases.
What do you mean by "ceases"? Do you mean that there's a transition from a scenario where time exists to a scenario where it doesn't? You cannot make a transition from a speed less than ##c## to a speed of ##c##. That's a consequence of the same postulates that lead to the notion of time dilation.
 
  • #6
Karl24 said:
Summary:: What's the experience of travel like for a photon?

We know that as speed increases, time slows, and at the speed of light time apparently ceases. Imagine a hypothetical hitch-hiker sitting on a photon and speeding through the universe at -- well, the speed of light. If time has stopped for him (her?), what is his experience of his journey? Are all locations and all times along his path of travel an instantaneous 'everywhere' and 'everywhen' for him?

And a subsidiary question: since the universe is finite, presumably there is eventually a frontier between space and no-space. Depending on where his photon was emitted, it could be that the hitch-hiker will never reach that frontier, because the accumulating expansion of space itself may exceed his rate of travel. But assuming the journey began somewhere already near the edge of space and the frontier was reachable, what happens when he reaches it? Does his mere presence extend the universe, and he continues merrily on his way? Or does he bounce back? Or cease to exist? Just wondering, before I book my ride!
We can see back in space just short of 13.8 billion years when the Big Bang begin. At the 13.8 limit space is expanding at the speed of light and creates an effective edge to what we can know. If we do the calculations that edge is now out 46 billion light years since it immitted light at the beginning of time.
 
  • #7
Moderator's note: A post has been deleted and the thread, which was temporarily closed for moderation, has been reopened.
 
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  • #8
DPH said:
At the 13.8 limit space is expanding at the speed of light
No, not at all. The stuff at the outer edge of our observable universe is receding at about 3c.

And, even aside from that, saying that "space is expanding at the speed of light" is an utterly meaningless statement. Expansion is a RATE, not a speed.
 
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Related to Experience Travel on a Photon: Hitch-Hiker's Guide to the Universe

1. What is "Experience Travel on a Photon: Hitch-Hiker's Guide to the Universe"?

"Experience Travel on a Photon: Hitch-Hiker's Guide to the Universe" is a theoretical concept that proposes using a photon, the smallest unit of light, as a means of travel through the universe. It is based on the idea that photons have no mass and can travel at the speed of light, making them a potentially efficient mode of transportation.

2. How would one travel on a photon?

The exact method of traveling on a photon is still a subject of debate and research. Some theories suggest using advanced technology to manipulate and harness the energy of a photon, while others propose using the natural properties of photons, such as their ability to travel at the speed of light, to propel a spacecraft.

3. Is "Experience Travel on a Photon" possible?

At this point in time, "Experience Travel on a Photon" is still a theoretical concept and has not been proven to be possible. However, with advancements in technology and further understanding of the properties of photons, it is not entirely impossible in the future.

4. What are the potential benefits of "Experience Travel on a Photon"?

If "Experience Travel on a Photon" were to become a reality, it could potentially revolutionize space travel and exploration. It could allow for faster and more efficient travel through the vastness of the universe, opening up new possibilities for human exploration and discovery.

5. Are there any limitations or challenges to "Experience Travel on a Photon"?

As with any theoretical concept, there are many challenges and limitations that would need to be addressed before "Experience Travel on a Photon" could become a reality. These include understanding and controlling the properties of photons, developing advanced technology, and ensuring the safety and sustainability of such a mode of travel.

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