# At c , will we live forever?

In summary: No, and my proof is my iron deficiency!I think that's the whole point of scientific enquiry, Adam, is that anything is NOT always possible.

I made a simple time dilation slider to experiment with the figs, i noticed at 100% c speed the time = 0
So does it mean that a person in a rocket at c speed, will live forever?

www.timedilationcalc.blogspot.com.au

Welcome to PF!

Well relative to someone on the Earth yes. However we can never go at the speed of light only approach it. The energy requirement becomes so great that even if we had all the energy in the universe we still couldn't quite reach 100%.

The person on the spacecraft will not feel as though they lived forever. They will feel they are ageing just like someone on the Earth.

I made a simple time dilation slider to experiment with the figs, i noticed at 100% c speed the time = 0
So does it mean that a person in a rocket at c speed, will live forever?

www.timedilationcalc.blogspot.com.au
Since we can't go 100% c, the question is meaningless.

i am here to learn

i am here to learn
Everyone is, btw are you Robert Downey Jr. ?

No, and my proof is my iron deficiency!

I made a simple time dilation slider to experiment with the figs, i noticed at 100% c speed the time = 0
So does it mean that a person in a rocket at c speed, will live forever?

www.timedilationcalc.blogspot.com.au
Theoretically , yes. Experimentally, no one knows.

ImperialThinker said:
Theoretically , yes. Experimentally, no one knows.
Can you please provide a legitimate online reference to support your theoretical statement?

ghwellsjr said:
Can you please provide a legitimate online reference to support your theoretical statement?
I agree with Imperial Thinker's statement , can you imagine ask Albert Enistien about a legimate reference to support his theoretical ideas in 1905, yet we all know now that he was right, anything is possible my friend

I think that's the whole point of scientific enquiry, Adam, is that anything is NOT always possible. That's what we're trying to figure out here, what is and what is not possible. And as far as we know, traveling at light speed and living forever for a massive object such as a human is not possible. Not even theoretically, as ImperialThinker asserted. Maybe "science fictionally," but not theoretically in terms of a consensus of contemporary physicists/cosmologists

can you imagine ask Albert Enistien about a legimate reference to support his theoretical ideas in 1905

Yes I can, and he would support his theoretical ideas.

yet we all know now that he was right, anything is possible my friend

That shows that you don't understand how science works. No, anything is not possible, and if you admit that Einstein was right, you can't agree with Imperial Thinker's statement, because what he says is that Einstein was wrong.

You can live arbitrarily long relative to Earth provided sufficient energy to accelerate and turn back at that speed.

In fact, it theoretically takes infinite coordinate time (distant observer's) to get to the event horizon of Schwarzschild black hole. However, you either never return or leave within short amount of time depending on your impact parameter (due to lack of stable orbit within 1.5 Schwarzschild radii).

Sorry, I need to clarify that the speed I am referring to means certain speed arbitrarily close to speed of light without actually reaching it.

I made a simple time dilation slider to experiment with the figs, i noticed at 100% c speed the time = 0
So does it mean that a person in a rocket at c speed, will live forever?
At light speed, you would not be alive.

Why not? If he could travel with the speed of light physics would be different, maybe he would be alive, or he would turn into a rabbit :D All we have is our physics and our world, in which there is no possibility to travel at the speed of light.

weirdoguy said:
All we have is our physics and our world, in which there is no possibility to travel at the speed of light.
In our world, the only way that I could think of is to evaporate every massive particles of an object into photons, such as annihilation and then pair creation, which travel at c. In that sense, I do not know any photon based organisms and I would assume the photons created not alive.

SR says that no matter what force you apply, you can never accelerate a massive object (like a person) to speed c. A massive object can however have a speed very close to c. In fact, you already do have a speed close to c, in some inertial coordinate system. There's always a particle such that you have a speed greater than 0.9 c in every inertial coordinate system that's comoving with it. Does that make you live forever, or almost forever? (No, it doesn't).

can you imagine ask Albert Enistien about a legimate reference to support his theoretical ideas in 1905

Sure, and his answer would be to simply give you the legitimate peer-reviewed references that he himself published in 1905.

berkeman
ImperialThinker said:
Theoretically , yes. Experimentally, no one knows.

No, theoretically and experimentally the answer is no. See below for why.

phyti said:
At light speed, you would not be alive.

A better way to say it, to avoid questions about whether the term "alive" could be applied to something made purely of photons, is that, to anything moving at c, whether a photon or anything else, the concept of "time" (more specifically "proper time", the time elapsed on a clock carried with the object) is meaningless. And since the concept of "living forever" depends on having a meaningful concept of time, the concept of "living forever" is also meaningless for anything moving at c. This is true both theoretically (because in the math of relativity, photons, and other objects that move at c, move on null worldlines, which do not have a meaningful concept of proper time) and experimentally (because the energy-momentum relation for photons, which is what verifies that they have zero invariant mass and move on null worldlines, has been extensively confirmed in experiments). So the answer to the OP's question is "no".

The question is not meaningless; it is an opportunity to explore.

You could - in theory - reach a speed arbitrarily close to light*. If you were to do so, you could manage to essentially outlive the universe. That's pretty close to forever. Of course, you would still only experience the same century lifetime, more or less, but you would be able to witness the universe aging and dying outside your spaceship window.

* as measured relative to some arbitrary local point

DaveC426913 said:
you could manage to essentially outlive the universe.

Even in this scenario, you would still only experience a finite lifetime, as you say. At some point that finite lifetime would end, and the universe, assuming it is going to keep expanding forever, which is our best current model, would still be there. It might be a cold, dead universe, with all stars long since burned out, but it would still be there.

If the universe will eventually recollapse to a Big Crunch, then you could, in theory, manage to live until the Crunch (but not beyond it, since the universe would end there and you with it).

I'm not sure that the OP meant to include these possibilities in his question, but he's welcome to weigh in.

PeterDonis said:
It might be a cold, dead universe, with all stars long since burned out, but it would still be there.
Well, if you see me cold and dead - but my body is still "there" on slab - I'd say that qualifies you as having "outlived" me. ;)

This is getting depressing...

PeterDonis said:
Even in this scenario, you would still only experience a finite lifetime, as you say. At some point that finite lifetime would end, and the universe, assuming it is going to keep expanding forever, which is our best current model, would still be there. It might be a cold, dead universe, with all stars long since burned out, but it would still be there.

If the universe will eventually recollapse to a Big Crunch, then you could, in theory, manage to live until the Crunch (but not beyond it, since the universe would end there and you with it).

I'm not sure that the OP meant to include these possibilities in his question, but he's welcome to weigh in.
Well, you could live as long as the universe, with no caveats if you had magic drive that could accelerate at more than constant g, as long as desired. For eternal uniform acceleration, though speed approaches c, proper time still approaches infinity. However, posit, e.g.

v = √(1-(1/t4)), from t=1 (with c=1)

and proper time is finite for infinite universe lifetime.

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DaveC426913 said:
The question is not meaningless; it is an opportunity to explore.

You could - in theory - reach a speed arbitrarily close to light*. If you were to do so, you could manage to essentially outlive the universe. That's pretty close to forever. Of course, you would still only experience the same century lifetime, more or less, but you would be able to witness the universe aging and dying outside your spaceship window.

* as measured relative to some arbitrary local point

If you never slowed down and returned, you would see everything else actually time-dilated. To you, things outside would be moving and aging slower than usual (once you account for the Doppler shift effects). If you moved arbitrarily close to the speed of light; however, you will see distances contract to arbitrarily small distances, so you will pass by things quite fast, stars would zoom right past you and become quite dense as far as you could tell.

To add to Matterwave's description, it is interesting to describe effects of beaming and aberration as well as Doppler.

As you approached ever closer to c:

1) The whole star field would be concentrated eventually in an incredibly intense blue dot in front of you. The rest of field of view would represent only what was directly behind you, stretched out over all except the blue dot. [extreme abberation].
2) The forward dot would be intense and blue shifted (soon, using the type of formula I gave for velocity growth) such that CMB radiation would be intense gamma radiation [beaming and Doppler.]
3) If you could still somehow image a clock you approach,it would visually appear to run approaching infinitely fast (Doppler). However, after factoring out classical Doppler (pure light delay), you would conclude, e.g. that a clock on which you see a million years register during an hour on your watch, corresponds to your history starting a billion years ago.
4) A clock that you are finally far enough past so it leaves the forward dot becomes red shifted to invisibility, but if you could see it, it would appear essentially frozen [receding Doppler].

PeterDonis said:
No, theoretically and experimentally the answer is no. See below for why.

A better way to say it, to avoid questions about whether the term "alive" could be applied to something made purely of photons, is that, to anything moving at c, whether a photon or anything else, the concept of "time" (more specifically "proper time", the time elapsed on a clock carried with the object) is meaningless. And since the concept of "living forever" depends on having a meaningful concept of time, the concept of "living forever" is also meaningless for anything moving at c. This is true both theoretically (because in the math of relativity, photons, and other objects that move at c, move on null worldlines, which do not have a meaningful concept of proper time) and experimentally (because the energy-momentum relation for photons, which is what verifies that they have zero invariant mass and move on null worldlines, has been extensively confirmed in experiments). So the answer to the OP's question is "no".
Assuming the initial conditions given, at c, nothing would happen regarding an organism.

Hypothetically, GR opens the possibility of a material object achieving c by reason of acceleration via g-fields, i.e., an external energy source.
Didn't Einstein remove the c restriction for the general theory?

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phyti said:
Assuming the initial conditions given, at c, nothing would happen regarding an organism.

Hypothetically, GR opens the possibility of a material object achieving c by reason of acceleration via g-fields, i.e., an external energy source.
Didn't Einstein remove the c restriction for the general theory?
I'm not sure how you draw those conclusions. You can't get there from here.

An organism cannot move at c, with a multitude of ways of looking at it. A particularly graphic one is that it would have infinite mass.

phyti said:
Assuming the initial conditions given, at c, nothing would happen regarding an organism.

Hypothetically, GR opens the possibility of a material object achieving c by reason of acceleration via g-fields, i.e., an external energy source.
Didn't Einstein remove the c restriction for the general theory?

It's not so much that GR "removes the restriction of traveling at c", it's that speeds in GR can only be meaningfully measured locally. To measure the speed of a distant object (w.r.t. you) is not always a well defined concept, and different definitions of "speed" will sometimes start to arise. Thus, in GR, the restriction of traveling at "c" is a local restriction simply because the concept of "traveling at c" itself is a local concept.

It seems to me that if time did stop then you'd no longer be alive!

phyti said:
Assuming the initial conditions given

You can't assume initial conditions that can't be realized.

phyti said:
at c, nothing would happen regarding an organism.

This doesn't follow. Photons move at c, and things happen regarding photons. The correct statement, as I said in an earlier post, is that the concept of "proper time" does not apply to photons. But proper time doesn't have to apply to photons for things to happen regarding them; that's obvious since we can run experiments involving photons in which things happen regarding them--they interact with other particles, are created and destroyed, etc.

PeroK said:
It seems to me that if time did stop then you'd no longer be alive!

Time does not "stop" for photons. The concept of "proper time" does not even apply to photons, so it can't "stop" for them.

PeroK said:
It seems to me that if time did stop then you'd no longer be alive!
We're getting into philosophical woo-woo territory here, but I'll just add one observation: if time were "restarted", you'd still be alive - so I'd argue you did not stop living.

Peter's answer is correct: when you try to describe a frame of reference at c, you get silly results.

PeroK
DaveC426913 said:
We're getting into philosophical woo-woo territory here, but I'll just add one observation: if time were "restarted", you'd still be alive - so I'd argue you did not stop living.

Certainly it would be fair to say that you hadn't actually died!

The theory of special relativity doesn't really discuss what happens "at v=c". It discusses what happens as a massive object approaches v=c. I am pretty sure that we can't define a valid reference frame for photons since the photon can never be taken to be at rest. for example.

nucl34rgg said:
The theory of special relativity doesn't really discuss what happens "at v=c".

It does for photons. It doesn't for objects with nonzero rest mass, as you point out; it just says that such objects can never reach c.

nucl34rgg said:
I am pretty sure that we can't define a valid reference frame for photons since the photon can never be taken to be at rest. for example.

You're correct, we can't. See our forum FAQ on this. But we don't need to define a "rest frame" for a photon to deal with photons using SR.