Towards Understanding Geometry of Time

How Gemma 2 2B represents time: PCA finds a clean two-axis temporal structure at layer 20 that individual GemmaScope SAE features dilute across many latents.
interpretability
code
visualisation
Published

June 2026

Geometric structure of temporal concepts and the limits of sparse autoencoders decompostion.

Dilution of “time”: PCA vs SAE features in Gemma 2 2B

(details to be described).

Kaggle’s defaults

::: {#cell-1 .cell _uuid=‘8f2839f25d086af736a60e9eeb907d3b93b6e0e5’ _cell_guid=‘b1076dfc-b9ad-4769-8c92-a6c4dae69d19’ trusted=‘true’ quarto-private-1=‘{“key”:“execution”,“value”:{“iopub.status.busy”:“2026-06-19T11:25:44.713263Z”,“iopub.execute_input”:“2026-06-19T11:25:44.714087Z”,“iopub.status.idle”:“2026-06-19T11:25:45.430611Z”,“shell.execute_reply.started”:“2026-06-19T11:25:44.714037Z”,“shell.execute_reply”:“2026-06-19T11:25:45.429740Z”}}’ execution_count=1}

/kaggle/input/datasets/nikolazhuk/interp-emotions-prompts/prompts/joy.py
/kaggle/input/datasets/nikolazhuk/interp-emotions-prompts/prompts/neutral.py
/kaggle/input/datasets/nikolazhuk/interp-emotions-prompts/prompts/temporal.py
Source: Kaggle's defaults

Environment setup

torch 2.10.0+cu128 | cuda 12.8 | device cuda

Load model and SAE

Loaded pretrained model google/gemma-2-2b into HookedTransformer
n_layers=26, d_model=2304
GPU allocated: 15.2GB / 15GB
SAE d_sae: 16384, d_in: 2304
{'d_in': 2304, 'd_sae': 16384, 'dtype': 'bfloat16', 'device': 'cuda', 'apply_b_dec_to_input': False, 'normalize_activations': 'none', 'reshape_activations': 'none', 'metadata': SAEMetadata({'sae_lens_version': '6.44.2', 'sae_lens_training_version': None, 'model_name': 'gemma-2-2b', 'hook_name': 'blocks.20.hook_resid_post', 'hook_head_index': None, 'prepend_bos': True, 'dataset_path': 'monology/pile-uncopyrighted', 'context_size': 1024, 'neuronpedia_id': 'gemma-2-2b/20-gemmascope-res-16k'})}

Reproduction of days-of-weeksFrom paper:NOT ALL LANGUAGE MODEL FEATURES AREONE-DIMENSIONALLY LINEAR: https://arxiv.org/pdf/2405.14860(residual PCA at layer 15)

Variance explained: [0.37461206 0.25319353 0.132533   0.12052249]
Cumulative: [0.37461206 0.6278056  0.7603386  0.8808611 ]

Encoding residuals ->feature activations

Days-of-wwek SAE decoder PCA

max act: 2040.0 | nonzero: 7208
max act: 2040.0 | nonzero: 7313
max act: 2040.0 | nonzero: 7231
max act: 2040.0 | nonzero: 7475
max act: 2040.0 | nonzero: 7314
max act: 2040.0 | nonzero: 7234
max act: 2040.0 | nonzero: 7276
max act: 2040.0 | nonzero: 7285
max act: 2040.0 | nonzero: 7203
max act: 2040.0 | nonzero: 7308
max act: 2040.0 | nonzero: 7222
max act: 2040.0 | nonzero: 7475
max act: 2040.0 | nonzero: 7310
max act: 2040.0 | nonzero: 7239
max act: 2040.0 | nonzero: 7274
max act: 2040.0 | nonzero: 7282
max act: 2040.0 | nonzero: 7210
max act: 2040.0 | nonzero: 7308
max act: 2040.0 | nonzero: 7225
max act: 2040.0 | nonzero: 7475
max act: 2040.0 | nonzero: 7310
max act: 2040.0 | nonzero: 7238
max act: 2040.0 | nonzero: 7271
max act: 2040.0 | nonzero: 7280
max act: 2040.0 | nonzero: 7202
max act: 2040.0 | nonzero: 7314
max act: 2040.0 | nonzero: 7229
max act: 2040.0 | nonzero: 7475
max act: 2040.0 | nonzero: 7313
max act: 2040.0 | nonzero: 7238
max act: 2040.0 | nonzero: 7268
max act: 2040.0 | nonzero: 7283
max act: 2040.0 | nonzero: 7218
max act: 2040.0 | nonzero: 7316
max act: 2040.0 | nonzero: 7234
max act: 2040.0 | nonzero: 7468
max act: 2040.0 | nonzero: 7309
max act: 2040.0 | nonzero: 7233
max act: 2040.0 | nonzero: 7274
max act: 2040.0 | nonzero: 7284
max act: 2040.0 | nonzero: 7193
max act: 2040.0 | nonzero: 7307
max act: 2040.0 | nonzero: 7219
max act: 2040.0 | nonzero: 7470
max act: 2040.0 | nonzero: 7310
max act: 2040.0 | nonzero: 7233
max act: 2040.0 | nonzero: 7268
max act: 2040.0 | nonzero: 7276
max act: 2040.0 | nonzero: 7211
max act: 2040.0 | nonzero: 7312
max act: 2040.0 | nonzero: 7232
max act: 2040.0 | nonzero: 7470
max act: 2040.0 | nonzero: 7311
max act: 2040.0 | nonzero: 7235
max act: 2040.0 | nonzero: 7280
max act: 2040.0 | nonzero: 7281
Found 429 candidate features active on day prompts

Load temporal prompts: past, present, future, counterfactual and hypotheticalFrom Kaggle’s imported dataset

Geometry at 8, 14, 20, 25 layers

Layer 8 done
Layer 14 done
Layer 20 done
Layer 25 done

Temporal category means at layer 20

max act: 2040.0 | nonzero: 7539
max act: 2040.0 | nonzero: 7409
max act: 2040.0 | nonzero: 7524
max act: 2040.0 | nonzero: 7504
max act: 2040.0 | nonzero: 7503
max act: 2040.0 | nonzero: 7528
max act: 2040.0 | nonzero: 7508
max act: 2040.0 | nonzero: 7520
max act: 2040.0 | nonzero: 7691
max act: 2040.0 | nonzero: 7531
max act: 2040.0 | nonzero: 7645
max act: 2040.0 | nonzero: 7846
max act: 2040.0 | nonzero: 7893
max act: 2040.0 | nonzero: 7535
max act: 2040.0 | nonzero: 7723
max act: 2040.0 | nonzero: 7597
max act: 2040.0 | nonzero: 7454
max act: 2040.0 | nonzero: 7613
max act: 2040.0 | nonzero: 7564
max act: 2040.0 | nonzero: 7724
           past: 20 prompts processed
max act: 2040.0 | nonzero: 7547
max act: 2040.0 | nonzero: 7494
max act: 2040.0 | nonzero: 7498
max act: 2040.0 | nonzero: 7586
max act: 2040.0 | nonzero: 7653
max act: 2040.0 | nonzero: 7507
max act: 2040.0 | nonzero: 7781
max act: 2040.0 | nonzero: 7417
max act: 2040.0 | nonzero: 7550
max act: 2040.0 | nonzero: 7392
max act: 2040.0 | nonzero: 7493
max act: 2040.0 | nonzero: 7570
max act: 2040.0 | nonzero: 7713
max act: 2040.0 | nonzero: 7620
max act: 2040.0 | nonzero: 7567
max act: 2040.0 | nonzero: 7579
max act: 2040.0 | nonzero: 7456
max act: 2040.0 | nonzero: 7476
max act: 2040.0 | nonzero: 7780
max act: 2040.0 | nonzero: 7566
        present: 20 prompts processed
max act: 2040.0 | nonzero: 7641
max act: 2040.0 | nonzero: 7522
max act: 2040.0 | nonzero: 7558
max act: 2040.0 | nonzero: 7594
max act: 2040.0 | nonzero: 7581
max act: 2040.0 | nonzero: 7584
max act: 2040.0 | nonzero: 7663
max act: 2040.0 | nonzero: 7790
max act: 2040.0 | nonzero: 7721
max act: 2040.0 | nonzero: 7666
max act: 2040.0 | nonzero: 7563
max act: 2040.0 | nonzero: 7727
max act: 2040.0 | nonzero: 7591
max act: 2040.0 | nonzero: 7613
max act: 2040.0 | nonzero: 7546
max act: 2040.0 | nonzero: 7372
max act: 2040.0 | nonzero: 7408
max act: 2040.0 | nonzero: 7619
max act: 2040.0 | nonzero: 7618
max act: 2040.0 | nonzero: 7609
         future: 20 prompts processed
max act: 2040.0 | nonzero: 7935
max act: 2040.0 | nonzero: 8004
max act: 2040.0 | nonzero: 8128
max act: 2040.0 | nonzero: 8183
max act: 2040.0 | nonzero: 7943
max act: 2040.0 | nonzero: 8124
max act: 2040.0 | nonzero: 8238
max act: 2040.0 | nonzero: 8123
max act: 2040.0 | nonzero: 8023
max act: 2040.0 | nonzero: 7977
max act: 2040.0 | nonzero: 7697
max act: 2040.0 | nonzero: 7868
max act: 2040.0 | nonzero: 7912
max act: 2040.0 | nonzero: 7928
max act: 2040.0 | nonzero: 7986
max act: 2040.0 | nonzero: 7992
max act: 2040.0 | nonzero: 7873
max act: 2040.0 | nonzero: 7783
max act: 2040.0 | nonzero: 7685
max act: 2040.0 | nonzero: 7886
 counterfactual: 20 prompts processed
max act: 2040.0 | nonzero: 7829
max act: 2040.0 | nonzero: 7854
max act: 2040.0 | nonzero: 8083
max act: 2040.0 | nonzero: 7973
max act: 2040.0 | nonzero: 7870
max act: 2040.0 | nonzero: 7886
max act: 2040.0 | nonzero: 7926
max act: 2040.0 | nonzero: 7876
max act: 2040.0 | nonzero: 8087
max act: 2040.0 | nonzero: 7886
max act: 2040.0 | nonzero: 7775
max act: 2040.0 | nonzero: 7857
max act: 2040.0 | nonzero: 7934
max act: 2040.0 | nonzero: 8015
max act: 2040.0 | nonzero: 8054
max act: 2040.0 | nonzero: 8279
max act: 2040.0 | nonzero: 7804
max act: 2040.0 | nonzero: 7836
max act: 2040.0 | nonzero: 7734
max act: 2040.0 | nonzero: 7958
   hypothetical: 20 prompts processed
max act: 2040.0 | nonzero: 8065
max act: 2040.0 | nonzero: 7430
max act: 2040.0 | nonzero: 7641
max act: 2040.0 | nonzero: 7597
max act: 2040.0 | nonzero: 7673
max act: 2040.0 | nonzero: 7861
max act: 2040.0 | nonzero: 7523
max act: 2040.0 | nonzero: 7679
max act: 2040.0 | nonzero: 8263
max act: 2040.0 | nonzero: 7745
max act: 2040.0 | nonzero: 7456
max act: 2040.0 | nonzero: 7660
max act: 2040.0 | nonzero: 7432
max act: 2040.0 | nonzero: 7689
max act: 2040.0 | nonzero: 7903
max act: 2040.0 | nonzero: 7417
max act: 2040.0 | nonzero: 7797
max act: 2040.0 | nonzero: 7889
max act: 2040.0 | nonzero: 7673
max act: 2040.0 | nonzero: 7594
        neutral: 20 prompts processed

top differential features per category


=== PAST ===
 feature_id  diff_score  past_mean  neutral_mean                                                    neuronpedia
       1858     24.0000    64.0000     40.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1858
       2230     16.2500    16.2500      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2230
       1548     15.5625    15.5625      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1548
       2914     14.8125    16.1250      1.289062  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2914
      12545     14.1875    14.1875      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12545
       6631     13.7500    52.2500     38.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/6631
       2229     13.0000    64.5000     51.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2229
       2238     12.8125    26.0000     13.187500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2238
      15383     11.5000    11.5000      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/15383
       5571     11.3750    12.1875      0.789062  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5571
       5890     11.0000    11.5000      0.474609  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5890
       1306     10.5000    10.5000      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1306
      12265      9.6250    12.5000      2.859375 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12265
       7116      9.5000     9.5000      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/7116
      10377      9.4375     9.4375      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/10377

=== PRESENT ===
 feature_id  diff_score  present_mean  neutral_mean                                                    neuronpedia
       1858    19.25000      59.25000     40.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1858
       6631    15.00000      53.50000     38.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/6631
       2230    14.31250      14.31250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2230
       2914    13.75000      15.06250      1.289062  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2914
      12545    12.75000      12.75000      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12545
       2489    12.43750      12.43750      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2489
       2238    12.18750      25.37500     13.187500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2238
       7116    11.62500      11.62500      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/7116
       2229    11.50000      63.00000     51.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2229
      12265    11.00000      13.87500      2.859375 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12265
       5890     9.75000      10.25000      0.474609  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5890
       3971     8.87500      14.25000      5.375000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/3971
       9768     8.75000      44.00000     35.250000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9768
      15383     8.68750       8.68750      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/15383
       4373     7.59375       7.59375      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/4373

=== FUTURE ===
 feature_id  diff_score  future_mean  neutral_mean                                                    neuronpedia
      16148     17.5000      17.5000      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/16148
       2230     16.3750      16.3750      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2230
       6631     15.7500      54.2500     38.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/6631
       2229     14.5000      66.0000     51.500000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2229
       1858     13.0000      53.0000     40.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1858
       9520     12.3750      12.3750      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9520
       7569     12.1250      12.1250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/7569
       1322     12.0000      12.4375      0.421875  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1322
       2238     11.9375      25.1250     13.187500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2238
      12265     11.8750      14.7500      2.859375 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12265
      12545     11.5625      11.5625      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12545
       5890     11.1250      11.6250      0.474609  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5890
       1630      8.6250       8.6250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1630
       7116      8.4375       8.4375      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/7116
      12341      8.2500       8.7500      0.519531 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12341

=== COUNTERFACTUAL ===
 feature_id  diff_score  counterfactual_mean  neutral_mean                                                    neuronpedia
       1858     29.0000              69.0000     40.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1858
      15383     19.0000              19.0000      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/15383
       5571     18.8750              19.6250      0.789062  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5571
       2238     17.2500              30.5000     13.187500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2238
      14267     17.0000              17.0000      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/14267
      12545     16.2500              16.2500      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12545
       2230     14.1250              14.1250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2230
       9909     13.7500              22.0000      8.250000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9909
       5890     13.3125              13.8125      0.474609  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5890
       9070     12.5625              12.5625      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9070
      12265     11.6250              14.5000      2.859375 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12265
       9492     11.1250              11.1250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9492
       1720     11.0625              11.5000      0.437500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1720
       5371     11.0625              11.8750      0.828125  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5371
       7116     10.1875              10.1875      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/7116

=== HYPOTHETICAL ===
 feature_id  diff_score  hypothetical_mean  neutral_mean                                                    neuronpedia
       1858    18.25000           58.25000     40.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1858
       1720    16.75000           17.12500      0.437500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1720
       2238    13.68750           26.87500     13.187500  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2238
       5890    10.25000           10.75000      0.474609  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5890
       5571    10.25000           11.06250      0.789062  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/5571
       2230     9.31250            9.31250      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2230
      15383     7.90625            7.90625      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/15383
      16148     7.56250            7.56250      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/16148
      12265     7.00000            9.87500      2.859375 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12265
      14041     6.81250            7.31250      0.507812 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/14041
       9635     6.68750            6.68750      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9635
       9070     6.25000            6.25000      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/9070
       1548     6.18750            6.18750      0.000000  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/1548
       2956     5.93750            6.31250      0.373047  https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/2956
      12545     5.90625            5.90625      0.000000 https://neuronpedia.org/gemma-2-2b/20-gemmascope-res-16k/12545

temporal geometry PCA

Variance explained: [0.4102727  0.33915818 0.13833533 0.11223382]
Cumulative:         [0.4102727  0.7494309  0.88776624 1.        ]

Pre-prompt scatter

past: done
present: done
future: done
counterfactual: done
hypothetical: done


Silhouette score in PC1-2: -0.119
Silhouette score in PC1-4: 0.010
Interpretation: > 0.25 = clear cluster structure, 0.1-0.25 = weak structure, < 0.1 = mostly overlapping

Silhouette in means-basis (PC1-2): 0.196
Silhouette in means-basis (PC1-4): 0.310

:::

Run in Kaggle